Diagnostic game-changers

Autotechnician readers share their thoughts on what tools and techniques have changed their approach to diagnostic investigation

To excel at a task, it is not enough to have the right tools for the job, but to know how to use them to their full potential and how to apply them efficiently to the specific task in hand. As vehicles continue to break away from a simpler, mechanical powerhouse they once were into a finely tuned system of communicating microchips, is it possible to know every system, from every manufacturer, inside out? There are many fine master technicians out there who tackle this complicated tech and do their homework at every opportunity; sharing ideas on forums, training regularly, following case studies in magazines and logging the more awkward jobs that come through their doors in order to develop ever-more sophisticated repair techniques. And after speaking to hundreds of technicians over the years, from apprentices who are starting out in their career to the best repairers in the UK – succeeding in attaining that first-time fix is, like every challenge in life, all about having the right attitude.

We asked a number of technicians, including two chaps who have moved from the garage floor into diagnostic tool development roles, what they considered to be the tools, techniques or bits of training they have picked up along their journey which they consider game-changing in their approach to diagnostic work, in the hope that some nuggets of information may strike a chord with you dear reader, and serve as inspiration to keep striving for that perfect, first-time fix.

Martyn Langbridge, Cheltenham & Gloucester Autocentre in Cheltenham
Martyn believes that it’s the preparations that enable correct diagnosis rather than the art itself…

“Having the right attitude to running your workshop and diagnosing faults is key. The best places to network and meet people who can inspire you – such as Frank Massey, James Dillon and Andy Savva – are events and exhibitions. These trainers give you the correct attitude that attending courses isn’t a burden, cost or waste of time, but vital. I have had some excellent training from James (Dillon of Technical Topics) that has progressed our business.

“There are so many tools that help us diagnose and I wouldn’t be without any of them, but for me it’s all about everything except actually doing the job – staff, attitude, training, tooling, image, parking, reception… all come before diagnosing or repairing a vehicle.”

 

Andrew West of Erme Valley Autos in Ivybridge, Devon

pico“There are a couple of things that I consider a bit of a ‘game changer’. The main one was the Pico WPS500X pressure transducer, which opened up a whole new aspect of diagnosis, enabling examination of cylinder compression and valve events, amongst many other uses.

“My eyes were opened when I met Jean and Frank Massey, who showed me that these hidden signals were present in automotive electrics and they could be viewed with an oscilloscope, which I was completely oblivious to at the time.

“I attended a training event with Mark Carter, who explained (what now appears simple) how to calculate the theoretical air mass entering an engine. This has greatly helped with the diagnosis of air mass meters & EGR valve operation.”

 

Matthew Pestridge of D&D Autos in Ashford, Kent

Pestridge“I have been doing diagnostics for quite a few years now and one of the key things I have learnt is the importance of having a methodical approach. When a vehicle comes in, I will have an action plan so that I know what I am doing and where I am heading. This may sound simple, but I have seen many people start to diagnose a job only to get lost in their own thought processes. The consequence of this is a loss of time and possible misdiagnosis.

“I have attended several training courses over the years, the majority with Bosch and several with independent training providers, such as Frank Massey, ranging from basic electrics, hybrid vehicles to diesel systems – all have been extremely beneficial in how I diagnose a vehicle. Training has always been a priority for me and is an ongoing activity; I am always looking for new training avenues that will broaden my horizon. It’s a means to keeping abreast of new technology, especially as the modern vehicle gets more complex!  It’s also a great forum for sharing ideas with fellow colleagues in the industry.

“Diagnostic equipment has changed a lot over the years. There was the Crypton Act that was purchased back in the 90’s and a VAG 1552 (I still have both in a box in my office) to now using pass- thru and dealing with the manufacturers direct to do the more special functions. As an independent garage working on all makes, having one piece of equipment that caters for every manufacturer and getting the repair data has been challenging, however, I have made some significant investments in various pieces of equipment over the years, which have helped me keep abreast of new technology. Despite this investment, diagnosing all makes is difficult, especially when it comes to coding and programming the parts once they have been diagnosed. Even just checking for the latest software can be a headache, however, this is where having the knowledge of using the manufacturers’ websites comes in extremely handy!”

 

Anthony Pickering of CBF Service Centre in Suffolk

“It is hard to pick one specific ‘game changer’ that has made my diagnosis life easier. It’s a combination of training (live and online), using good tooling (oscilloscope, electric test meters, smoke generator, pressure/vacuum gauges) and combining the two, together with lots of practice of different testing techniques to hone a fault-finding technique which has reliable results.

“I still learn something new every day.”

 

Mark Banks, Diagnostic Development Engineer at Robert Bosch

mark“For me, the tool that changed my outlook to vehicle diagnostics was a good quality digital multimeter. The moment that the ‘Diagnostic Penny’ really dropped for me, about 20 years ago, was learning about, and understanding the principle of, ‘volt drop’ in electrical circuits.

“In an automotive world of ever-advancing technology, it is so easy to over complicate a job by missing the basic initial tests when looking for an electrical fault on a vehicle. The benefit of volt-drop testing is that you are examining the electrical circuit in its operating state, which is the best way to spot a problem. Bosch Automotive run an excellent training course called VSE1 – Essential test procedures, which covers this topic and is often an ‘eye opener’ for many technicians that attend.”

 

Lee Pritchard of Bowydd Garage in Gwynedd

“When doing day-to-day jobs and from a diagnostic point of view, the tool I couldn’t do without is the ‘Smoke machine’. I was introduced to it a few years ago on a Diesel training course by Technical Topics. The smoke machine is an excellent tool for flushing out such faults as Sticking EGR valves, intake leaks and vacuum pipe leaks, where access is very limited.

smoke“A few recent jobs we had in with a sticking EGR was the 1.6 VAG diesel engine, where the EGR is at the back of the engine. It’s very awkward to access, but with the smoke machine, no dismantling was required to diagnose. The smoke machine has become one of the first steps in the diagnostic process in our garage. Thinking back to when I was trying to diagnose faults before using this, I recall how much time and effort I was wasting – now I can do an evaluation of the complete intake system in under 10 minutes, making it a big time saver. We still hear of a lot of local dealerships are still not using this tool.”

 

 

Ainsley McEwan, semi-retired from McEwan’s Garage in Derby

“It’s difficult to pick one item because each piece of equipment, or training over the years, seemed to interlink, but I think one of the most important for me, was back in the mid 1990’s when I bought a digital oscilloscope.

“I had used CRT scopes with engine tuners but the digital scope, with the ability to display multiple channels and freeze/save the images, really helped me to start understanding sensor operation and their relationships. The digital oscilloscope gave me the confidence and knowledge to diagnose faults others couldn’t and the fact I had four at one time says it all.”

 

Andy Gravel, ADG Autotech in Scunthorpe

gravel“I was first introduced to the WPS500X Pressure Transducer at James Dillon’s Diagnostic boot camp and returned home inspired, and had one on order within days. With the PicoScope already being an everyday essential tool, the WPS500X makes an impressive addition. I was initially shown its use for in-cylinder compression testing and it quickly became apparent that its uses are endless.

“To be able to test and record pressure over time with the level of detail and accuracy available with this tool, makes testing the likes of an intermittent fuel pressure issue a one-man job. The data can be analysed, saved and shared with colleagues or customers, supporting the value of the diagnostic process.

“I most recently used this to test and record an engine oil pressure issue after a turbo failure. The vehicle was displaying a lack of power; the oil pressure was tested and was found to be low, causing the turbo failure. The customer failed to mention the oil pressure light remained on for an excessive amount of time after start-up, he was told by the dealership that this was nothing to worry about and probably a switch issue, so the customer took a little convincing that it was an oil pressure issue. Having the data recorded and printed to display to the customer as evidence made my job easier.”

 

Steve Smith, previously a master tech at a Toyota dealership, now Automotive Application Specialist at Pico Technology

volts“A game changer for me was learning Ohm’s Law and voltage drop, and applying them in the real world. This might sound very ‘theoretical’ but it really is where theory meets practice. I knew I had to understand these electrical principles in order to provide what I saw at the time as job security – given my colleagues were happy with routine work and avoiding electrical work like the plague!

“Having firm electrical foundation knowledge that I could apply in the real-world during my YTS (that’s the Youth Training Scheme to our younger readers! Ed) soon brought all kinds of work outside of the norm. By no means did I fully understand what I was working with but once again, understanding the principles and theory got me through and has paid dividends. The training I received during ‘day release’ to college back in 1984 to 1988 – I still keep in touch with my electrical lecturer today. I owe him big time.

“The best tool would be the one I invested heavily in back in the 80’s and still have today. I paid around £270 with the interest, which is a lot when you earn £25 per week! It was the simple Multimeter made by a competitor that I cannot mention, but their name begins with ‘F’ and ends in ‘E’ with ‘LUK’ in the middle. Great tool, great quality, lasts forever.”

 

Kim Doerr, K D Auto Services in Bedford

kim“In the early days of my diagnostic experience we had Sun and Crypton machines, they kicked off my interest in fixing the actual fault and not just guessing. The live oscilloscope on these machines was always the most interesting part and has evolved into what I have to say is the biggest game changer of all.

“To actually see what is going on in a circuit is vital on modern vehicle systems and I couldn’t do half of my work without it.

jukebox“For me, the PicoScope is the best tool I have and I had an unusual job for it recently. My 1957 Jukebox was playing up, not selecting correctly, the amps clamp on the PicoScope showed a much shorter millisecond duration on some of the selections. It turned out to be a very slight mechanical adjustment of a solenoid. If it had an ECU I’m sure some people would be throwing a new ECU at it!

“I have bought some diagnostic scan tools just to stay up to date and they have cost me dearly, but if I hadn’t, I’d have been left behind many years ago… Life is one great big learning curve.

“I’ve used VCDS for many years – and has paid for itself many times over. I have many other scan tools because not one will do everything. I use Smoke Pro a fair bit too, this is one of those tools that never gets outdated and has earned it’s keep – simple and effective!”

Do you have any tips to share? Let us know via our Facebook page at www.facebook.com/Autotechmagazine

Win a scope at our Big Day Out!

There’s just under three weeks to go until autotechnician’s Big Day Out takes place at Laser Tools on Saturday 3rd September, where guests will benefit from the vast technical know-how of James Dillon, Frank Massey, Pico’s Steve Smith and Andy Crook of GotBoost. The event will run between 10am and 4pm at Tool Connection in Warwickshire and will bring independent technicians and workshop owners together with trainers and the team at autotechnician magazine to share techniques and ideas in an informal setting.

Training presentations

gallerySteve Smith will connect to his vehicle and display live data throughout his presentation. He is considering Diesel relative compression using PicoScope in a non-intrusive fashion, Cam-Crank synchronisation, cylinder balance – introducing post waveform analysis of the crankshaft signal using the Math Channel, in-cylinder analysis using the pressure transducer and fluid pressure evaluation/analysis using the pressure transducer!

Frank Massey has suggested presenting the energy saving Audi 888 engine, explaining its flexible fuelling, variable valve lift & timing, in addition to his thoughts on the connected car movement.

Andy Crook is looking to do something on data collection, showing some of the techniques used in motorsport that could aid diagnostic process in the workshop.

Exclusive offers and prizes on the day

laser 600Guests can take advantage of a 10% discount on all Pico products brought on the day and one lucky raffle winner will take home a 2-Channel Starter kit, if they already have a PicoScope, the prize can be exchanged for a 2,000A current clamp with a Flexi COP probe.

Comma will be handing out goodie bags to people who sign up to its free Professional Partner Programme on the day and a voucher for 300K PPP points will be given away in the raffle which can be exchanged for a TV, iPad or ten pairs of Comma overalls!

 Don’t miss out!

Tickets priced £59.50 plus VAT are available by calling Nicola on 01634 924 406, or by emailing Nicola@autotechnician.co.uk. Attendance will count towards your CPD and the cost can be claimed back against your annual tax bill.

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Video gallery

AutoMate Training give a brief overview of how a vehicle’s climate management system now electronically controls cabin climate; zoning and zone control and the systems implemented to detect and control cabin carbon dioxide levels…

Delphi’s 48-volt mild hybrid system offers more affordable solution to greener future…

https://youtu.be/_rVh4CdnDE0

Investigation of a coil on plug ignition system using a four-channel PicoScope and a coil-on-plug ignition probe…

VW Polo 1.2 3-Cyl | Misleading fault codes

When it comes to diagnosis a cool head must be maintained when all around appears to be crumbling. Our relationship with the customer pays dividends during diagnosis where rapport is essential when things appear to go from bad to worse.

It is very easy to jump to conclusions when the evidence gathered during diagnosis points to a particular component. It is at this stage we should take stock and step away to ponder before we commit to our diagnosis.

James Dillon shares a very good comment surrounding commitment to a diagnosis:

“When replacing a component and you discover the fault is still apparent you then ask yourself, what else could it be? Why not ask yourself this same question before replacing the suspect component?”

Asking yourself this question before committing to your diagnosis could potentially lead you to the actual cause and avoid embarrassment. The case study below is one such example where taking a step back at the correct point in time saved the day.

The vehicle in question is a 1.2 3-cylinder VW Polo. The vehicle’s owner complained of power loss and intermittent cutting out at junctions (the customer had also requested a long overdue service).

A basic inspection (including a road test) confirmed no cutting out but a clear lack of performance under acceleration.  A vehicle scan of the engine management revealed fault codes P0106 relating to MAP Sensor Implausible Signal and P0172, Fuel System Too Rich (Both conditions recorded as intermittent).

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An inspection of live data confirmed plausible signals from the MAP Sensor, but a fuel trim value of -14% indicated considerable fuelling correction by the ECU. An emission and fuel quality test proved inconclusive and so attention was focused on the detection condition of the offending MAP Sensor fault code, P0106. The detection conditions surround the power, ground and output signals of the MAP sensor in relation to engine speed, load and throttle position.

The integrity of power and ground proved stable with the engine running and so the functionality of the sensor had to be proven.

Removal of the Map sensor highlighted typical contamination to the sensing tip as a result of crankcase breather fumes/oil mist throughout the intake manifold. A brief clean of the MAP Sensor and intake manifold port resulted in improved functionality of a component that could be attributed to the lack of power, negative fuel trim and cutting out.

A note here surrounding power, ground and signal of components such as MAP sensors:

Whilst it may be tempting to measure the signal wire only (based on the fact that if the signal is OK then power and ground must be OK), true evaluation of any component must include power, ground and signal simultaneously, unfortunately consuming three channels of your scope.

The waveform below confirms a rapid response of the MAP sensor in relation to a WOT test, accompanied with the characteristic pulsations at idle speed that can be attributed to valve open and close events.

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A road test once again confirmed no cutting out but the lack of power remained. As a result further diagnosis time was now required. It is at this point customer rapport comes into play as we have used up what is fondly referred to as the Golden Hour. The Golden Hour is the one hour labour agreed with the customer to carry out a vehicle assessment and initial diagnosis resulting in a quote for the required repair, or a request for additional labour time/charge to continue the diagnosis.

Authorization via the customer allowed for an additional 1 hour labour. During this time the detection conditions surrounding fault code P0172 were pursued to include: fuel pressure, intake and exhaust integrity, 4-Gas emissions and combustion efficiency based on O2 signals. All proved inconclusive!

During the above tests it was noted that cranking time had increased before the engine would start accompanied with lumpy idle speed before stabilising. Could this be compression related as we seem to have exhausted all other possibilities?

A dynamic valve timing check was carried out utilising Camshaft and Crankshaft signals whilst drawing comparisons against an identical vehicle waveform, downloaded from the Pico Waveform Library (no fault codes had been reported of Crankshaft/Camshaft correlation!).

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At last, a breakthrough in the diagnosis and something conclusive to follow. I have to say at this point, this is the second time I have used the Waveform Library during real-life diagnosis to confirm valve timing errors and both times it has proved to be successful.

Looking at the waveforms above we have an error of approximately ½ a crankshaft tooth which equates to a timing error of 3 degrees of crankshaft rotation:

Crankshaft Pick-up has 60 teeth -2 teeth for engine position reference:

360 degrees of crankshaft rotation divided by 60 teeth = 6 degrees
Each tooth equates to 6 degrees of crankshaft rotation.
Therefore ½ a crankshaft tooth (the gaps between pick-up teeth) equates to 3 degrees
With the camshaft running at ½ engine speed, 3 degrees of crankshaft rotation equates to 1.5 degrees of camshaft rotation.

Here we are looking at a small correlation error that would appear to be outside the detection of the PCM given no correlation codes have been recorded! Could this error be responsible for our Map sensor and fuel trim codes?

In order to qualify this valve timing error the rotation rulers were used to indicate 360 degrees of crankshaft rotation between each engine position reference point (missing teeth) of the crankshaft sensor signal.

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With the rotation rulers in position the time rulers can be used to indicate not only time, but degrees of rotation with reference to the position of the rotation rulers (0 – 360 degrees).

Placing the time rulers at the falling edge of the 30th tooth of the Crankshaft pick-up and the rising edge of the Camshaft pick up, the time rulers indicate just over 2 ms and 3 degrees (highlighted in green) of Crankshaft/Camshaft correlation error or phase shift, confirming our calculation above.

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Further analysis of the Camshaft timing error highlighted an alarming shift in the correlation during engine cranking (see above). Here we can see a shift in the relationship between the Crankshaft and Camshaft by 1.5 teeth (9 degrees of crankshaft rotation) confirming our timing chain to be skipping teeth of the timing gears.

With the confirmation of shifting valve timing, the pressure transducer was installed into each cylinder for an overview of the effects on peak compression where all were found to be normal. However, an exhaust back pressure of 1.12 bar (cranking) was clearly evident across all cylinders (see image below of all 3 cylinders overlaid using the reference waveform feature of PicoScope).

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Could the exhaust back pressure be a result of shifting valve timing (1.5 teeth) or a result of an obstruction within the exhaust itself? Both have the potential to effect all cylinders equally and both could produce the symptoms described by the customer (lack of power, fuel trim correction and cutting out).

The oxygen sensor was removed and the compression hose of the WPS500X (with compression hose adaptor TA220 M18) was installed into the exhaust manifold in order to measure the back pressure during cranking.

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The waveform above proves conclusively our exhaust back pressure is not a result of a blocked exhaust given the back pressure in the cylinder had climbed to 10 bar! The back pressure via the O2 sensor aperture (outside of the cylinder) returned a value of 165.3 mbar.

Things had obviously gone from bad to worse as our cylinder exhaust pressure had climbed from 1.12 bar to 10 bar! This was now getting serious and expensive as the valve timing must have slipped even further for such an increase in the cylinder pressure during the exhaust stroke. A physical valve timing inspection revealed the degree of our valve timing error!

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Interesting note here was the peak compression remained high at 13.4 bar during cranking, yet our exhaust valve timing had slipped in the advanced direction by approximately 45 degrees. Had a conventional compression gauge been installed instead of the pressure transducer, the offending exhaust stroke cylinder pressure would not have been discovered leading to prolonged and possible misdiagnosis.

Why such a shift in valve timing?

Initially 9 degrees (max) at the Crankshaft to 45 degrees at the Exhaust camshaft!

I suspect a combination of:

All the above had somewhat altered the loading on the timing chain presenting irregular backlash on a worn timing chain/gears resulting in the dramatic shift in valve timing.

I think it’s worth mentioning the potential error when inspecting static valve timing using the relevant timing gear locking tools.  In the case above where we have a valve timing shift of ½ a tooth, such a small deviation can be overcome when locating locking pegs and Camshaft alignment tools due to backlash in the worn timing chain/gears. A degree of movement and backlash in the worn timing chain/gear arrangement will allow for the correct alignment of timing gear locking tools suggesting the valve timing to be correct!

Equally when carrying out a dynamic valve timing check using Crankshaft and Camshaft signals, whilst we can measure the slightest deviation in Crankshaft and Camshaft correlation we must remain aware of the location of the Camshaft Sensors when dealing with multiple Camshaft engines.

In the example above the camshaft sensor detects the position of the Inlet Camshaft only and assumes the position the Exhaust Camshaft to be correct. Assumptions must never accompany diagnosis.

True evaluation of valve timing is therefore a threefold process using a combination of static and dynamic checks accompanied with in-cylinder pressure measurements to confirm individual cylinder valve timing.

  1. Static valve timing will ensure the correct position of Crankshaft and Camshafts using locking pins. However, depending on how these shafts are locked, the relationship between shafts and timing gears maybe incorrect. Remember it is also possible to install Crankshaft and Camshaft locking tools with excessive backlash.
  2. A dynamic valve timing check (measuring Crankshaft and camshaft signals) will confirm the correct valve timing and display backlash but only relevant to the position of the Camshaft Sensor. With our vehicle above, the Camshaft sensor measures the position of the Inlet Camshaft only and not the Exhaust Camshaft!
  3. In-cylinder measurement will confirm the correct valve timing dynamically, allowing for backlash and regardless of the position of the Crankshaft and Camshaft sensors. Not only that, we can verify the dynamic valve timing for each individual cylinder!

So why do we need to measure the valve timing of individual cylinders when we have verified Crankshaft and Camshaft positions, zero backlash and the correct relationship between all timing gears and shafts?

What about valve clearances? (See our Subaru case study for more info: https://www.picoauto.com/library/case-studies/2012-subaru-flat-4-cylinder-misfire-p0302)

How about: worn camshaft lobes, poor alignment or installation of Camshafts, broken/insecure rockers, compressed hydraulic lifters or Camshaft lobes that have spun independent of the Camshaft? All these conditions will adjust the independent valve timing of each cylinder.

Another consideration; engines that utilise variable valve timing! Here we need to disable the relevant valve actuator in order to restore the engine to a default valve timing position (often the maximum retarded safe valve timing position). With the valve timing fixed, individual cylinder valve timing can be measured.

With all the above in mind, could we also have damage to an inlet or exhaust valve as a result of “collision” between the valve gear and piston? Our in-cylinder pressure waveform would suggest not given we can generate over 13 bar on the compression stoke and 10 bar once again during the exhaust stroke. (Deformed valves would result in zero compression values)

Permission was given by the customer to inspect the timing gear/ chain assembly for wear and provide an assessment of the potential costs involved for repair.

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Like any valve timing error we all know the potential for valve damage and so it only seemed logical to momentarily run the engine and confirm the integrity of the valve gear before committing to a timing chain repair only! In order to run the engine, the sump pan was re-installed and primed with oil to maintain oil pressure, whilst timing chain tension was managed using a pry bar to ensure zero backlash.

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The obtained results were devastating to say the least as the engine would not run, accompanied with excessive cranking speed and popping via the intake and exhaust system that certainly spelt the end for this engine; or did it?

The compression test results below suggested compression loss and individual in-cylinder valve timing errors! However, the expansion pocket formed at the base of the expansion stroke confirmed the Intake and Exhaust valves to be seating correctly, therefore not deformed!

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I mentioned at the start of this case study “It is very easy to jump to conclusions when the evidence gathered during diagnosis points to a particular component. It is at this stage we should take stock and step away to ponder before we commit to our diagnosis” .

I also mentioned how “taking a step back at the correct point in time saved the day“, well here it is.

In the heat of diagnosis and the results gathered to date, I was most certainly going to recommend the cylinder head be removed for further examination until my colleague (Kevin at Ives Garage) suggested the following:

Could these new symptoms (excessive cranking speed, intake and exhaust popping) be attributed to hydraulic lifter/ valve clearance characteristics as a result of Camshaft rotation by hand with insufficient oil pressure to replenish the lifters? If so, how could we prove this scenario?

How about temporarily installing the timing chain whilst cranking the engine (spark plugs removed) and monitoring the cylinder pressure during the replenishment of the hydraulic lifters? It was most certainly worth a shot!

Take a look at the waveform below where we can see the peak compression build from 2.7 bar to 7.6 bar (cyl 2) after 3 minutes of cranking. This can only be attributed to the progressive correction of individual valve timing and valve seating, as a direct result of the replenishment of the hydraulic valve lifters. It would be very difficult to visualize this event whilst plotting the build in compression against time using a conventional compression gauge. Here we now have the evidence required to support a timing chain/timing gear replacement only (the cylinder head can remain intact).

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Permission was given by the customer to replace the timing chain set, whereby upon reassembly (and a little cranking) the vehicle ran as normal with no fault codes and restored power.

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The waveforms above highlight our in-cylinder pressure and in-cylinder-valve timing after fix at idle speed and the Crankshaft and Camshaft correlation (after fix during cranking).

To conclude:

  1. Our contaminated Map Sensor could have been responsible for our original symptoms but cleaning and retesting the sensor with PicoScope confirmed a Map Sensor was not required.
  2. Excessive timing chain “whip” and back lash created implausible manifold pressure values as a result of momentary valve timing errors, also resulting in PCM fuelling corrections and cutting out. Using PicoScope to measure dynamic valve timing highlighted a timing chain wear issue.
  3. Remember there were no Camshaft/Crankshaft correlation codes reported by the PCM and so no errors highlighted using a scan tool!
  4. The use of the WPS500X pressure transducer initially highlighted the minor valve timing error and then of course the major valve timing error that presented itself during diagnosis. The use of a conventional compression gauge would have missed both these events.
  5. Continued use of the WPS500X pressure transducer with PicoScope prevented unnecessary removal of the cylinder head during our engine integrity test. Here we could monitor the build in compression against time during the replenishment of the hydraulic lifters.
  6. Once repaired, the WPS500X pressure transducer was utilised to qualify the diagnosis, confirm the efficiency of the engine and provide documented evidence to the customer, supporting the diagnosis and repair costs.

Food for thought:

The evolution of the internal combustion engine and the need to reduce cost of ownership has seen a rise in chain driven engines.  There is most certainly a pattern forming with such engines where timing chains appear to stretch over time, accompanied with questionable tensioner efficiency presenting Crankshaft/Camshaft correlation issues, that were not so frequent with belt driven engines.

Whether this is a result of the components used during manufacture, long-life service intervals, inferior engine oils or just an enthusiastic driving style, I am not sure. With this case study in mind, I think there is real value in dynamic valve timing checks during routine maintenance in order to obtain a timing gear signature for the engine under test.

These captured waveforms (timing chain signatures) can be used to monitor timing chain wear over time at each scheduled service protecting both the customer and workshop whilst presenting a potential repair opportunity.

Could we possibly a see a time where we revert to belt driven engines with recommended replacement intervals?

A big thank you to Pico Phil and Kevin of Ives Garage for their valued input during this challenging diagnostic journey.

VW Caddy | Lack of power, poor cold start

When it comes to diagnosis, perseverance is key and never has this been more relevant than in the following case study.

If at first you don’t succeed…you know the rest.
This case study follows post- purchase rectification of a 2007 VW Caddy 1.9 TDI (Engine code BLS). The Caddy was purchased at auction during the summer with the knowledge that the vehicle was not running at its best, but was “running”!

How this differs from a normal case study is that we do not have a customer complaint. In this case we are assisting with a local rectification project, when the owner called upon us as the going got tough.
The initial symptoms surrounded engine vibrations, engine noise, lack of power and poor starting.
To cut a very long story short the following items were replaced by the owner, curing the performance and balance issues, but leaving the starting issues:

Now had this been a customer’s vehicle, can you imagine the cost and explanation to go with each repair above? Knowing the history of the vehicle it proved too much of a temptation to not get involved and apply the PicoScope.
To begin, a basic inspection is invaluable and proved that all the above repairs had been carried out correctly and the fuel quality to be normal. The prolonged cranking symptom was confirmed and easy to reproduce regardless of engine temperature. Once running, the performance of the vehicle was fine with no drivability issues.

The engine warning light remained on but with reference only to EGR (which was removed by owner).
Cranking the engine in the fault condition confirmed air pulsations from the exhaust tailpipe but no fumes or smoke, suggesting no fuelling during the cranking period (cranking could often be as long as 15 seconds before the engine would fire and run!).
Thinking this through and accounting for the history above, compression, valve timing and injector signals had to be high on the list of probable causes knowing the timing belt had been replaced and no fumes or smoke were present during cranking at the tailpipe.

The capture below looks at Crankshaft-Camshaft-Starter Motor current and Injector signals during cranking. Here we kill a number of birds with one stone confirming that Crank and Camshaft signals are present, injection events are taking place, relative compressions peaks are even and cranking speed is correct based on the frequency calculation (see below on how we calculate cranking speed).

PicoScope 6 Relative Compression Data

 

 

 

 

 

 

Placing both time rulers to indicate 2 X compression peaks for each revolution of the crankshaft allows the software to calculate the frequency of these peaks (4.479 Hz). Frequency is measured in cycles per second, so multiplying 4.479 Hz by 60 we arrive at cycles per minute, better known as RPM. The test confirmed a cranking speed of 269 RPM.

Now we have confirmation injection events are taking place (at what appears to be TDC), how can we confirm the correct valve timing based on just a good signal from the Crank and Cam sensors?

This is where the Pico Waveform Library came into play. A browse of the waveform library using the search tool found a similar waveform from a known good engine, uploaded by a Pico user.

Access to the waveform library is via the File menu, requires an automotive PicoScope to be connected to your PC and a valid username and password to the Pico Automotive Forum.

PicoScope 6 Waveform Library Browser

PicoScope 6 Waveform Library Browser

 

 

 

 

 

 

The waveform library image demonstrates how searching for “VW, CADDY, 2001-2008, BLS” found an identical match from 1077 uploaded waveforms, allowing the Crankshaft and Camshaft correlation to be confirmed in a non-intrusive fashion.

Waveform Library

Waveform Library

 

 

 

 

 

 

Here, we can see the downloaded waveform from our waveform library with the correct valve timing.

Correct Valve Timing

Correct Valve Timing

 

 

 

 

 

 

The image below confirms a valve timing error with our VW Caddy, where the Cam signal does not align with the 8th peak of the crankshaft signal after the reference point.

Timing Error

Timing Error

 

 

 

 

 

 

Using the Rotation Rulers to indicate 0 to 720° degrees of crankshaft rotation and the zoom function of PicoScope to see more detail in the area of interest, we then introduced the Time Rulers to indicate the alignment error between the Crank and Camshaft signal. Not only can we measure the time difference between the camshaft and crankshaft, we can now measure the error in degrees of crankshaft rotation with reference to the rotation rulers. Looking at the zoom overview it is easy to see just how much detail has been revealed without compromising resolution given we have 1 Million Samples on one screen. We can clearly see each individual peak (tooth) of the Crankshaft and Camshaft signals and bear in mind the engine is running at idle speed!

The known good waveform confirms the relevant peak of the camshaft sensor signal to align directly with the 8th peak of the crankshaft sensor signal after the reference point.
The identical camshaft signal peak from our problematic Caddy does not align with the 8th peak after the reference point, but falls short by the equivalent of 2.6 degrees of crankshaft rotation. Looking at the timing error (2.6 degrees of crankshaft rotation) we know we are not looking at the timing belt being 1 tooth out as this would equate to 16°+ given the crankshaft sprocket has 22 teeth per crankshaft revolution (22 X 16 .3 = 360 degrees).

What became evident when removing the upper timing belt cover was the position of the camshaft sprocket in relation to the camshaft. The camshaft sprocket is secured by 3 M8 bolts through elongated holes allowing the “Torsion value” to be adjusted when fine tuning the valve timing via the relevant scan tool. With our Caddy we could see the original witness marks embossed into the camshaft sprocket indicating the point of origin prior to adjustments made during the timing belt installation.

Witness marks indicate position of M8 bolts prior to adjustment

Witness marks indicate position of M8 bolts prior to adjustment

 

 

 

 

 

 

A swift adjustment was made to return the sprocket to its original retarded position (based upon the witness marks) and the valve timing re-checked to confirm all is OK.

Camshaft signal peak aligns with 8th peak of Crankshaft signal after reference point

Camshaft signal peak aligns with 8th peak of Crankshaft signal after reference point

 

 

 

 

 

 

At this point it would have been great to say the starting issue had been resolved, but the truth is…NO! The poor starting symptom remained present with cranking time exceeding 15 seconds before start up! Time to recap:

The lack of exhaust fumes during the cranking stage led us to check to fuel delivery and pressure testing using the WPS500 pressure transducer.
Here we have utilised the WPS500 with a sight block to monitor the diesel positive priming pressure by connecting into the fuel feed hose, and the Tandem Pump delivery pressure via the test port built into the Tandem Pump body.

Sight block adapted to WPS500 allows fuel delivery to be monitored and measured

Sight block adapted to WPS500 allows fuel delivery to be monitored and measured

 

 

 

 

 

 

 

 

WPS500 used to measure Tandem Pump pressure via adapted hose

WPS500 used to measure Tandem Pump pressure via adapted hose

 

 

 

 

 

 

 

 

The waveform capture that followed confirmed our suspicions:
Priming pressure and fuel condition proved to be fine with no aeration of the diesel viewed through the sight block and adequate fuel priming pressure at ignition on and throughout cranking. The Tandem Pump however highlighted insufficient pressure for the engine to start (continual cranking would eventually result in sufficient pressure for the engine to start).

Insufficient pressure for engine to start

Insufficient pressure for engine to start

 

 

 

 

 

 

The waveform captured most certainly matches with the symptoms and explains why we have no initial combustion and no smoke via the exhaust during cranking. The question now is why (remember the Tandem Pump has been replaced and fuel priming is good)?
What became evident during the standby time (test equipment connected but engine off), fuel appeared to be passing from the sight block towards the engine followed by air bubbles until the sight block cleared of diesel fuel, suggesting a leak within the priming or high pressure circuit! The priming circuit could be eliminated as no external leaks were present. We therefore had to concentrate efforts on an internal high-pressure circuit leak, so focusing attention on injectors, the only items that had not been replaced!

The injectors were removed and reports were fed back by the owner that their fitment into the cylinder head was not as expected given they required minimum effort to be extracted from their respective locations. The images below highlight areas of concern surrounding the O-ring seals and their respective machined surfaces within the cylinder head and injector.

Poor formation of injector 'O' rings

Poor formation of injector ‘O’ rings

 

 

 

 

 

 

Score marks on machined surfaces

Score marks on machined surfaces

 

 

 

 

 

 

Due to the costs involved of replacing not only the injectors but the cylinder head assembly, nothing could be lost (other than time) by replacing the O-ring seals and hoping for the best! The good news then followed from the owner that the starting issue was cured, and so the scope just had to be connected to confirm all was OK.

On return to Pico, two sight blocks were used to monitor fuel priming and return pressures, whilst the Tandem Pump pressure was measured via the test port, utilising three WPS500 transducers. This gave a rare insight into the activity of the fuel delivery system of this TDI engine in real-time during the various stages of priming, cranking, idling, and shutdown whilst we had no reported starting or driveability issues.

The following image demonstrates the connectivity of three WPS500 pressure transducers:

Connectivity of three WPS500 pressure transducers

Connectivity of three WPS500 pressure transducers

 

 

 

 

 

 

Adequate priming pressure

Adequate priming pressure

 

 

 

 

 

 

The waveform above confirms adequate priming pressure and a rapid build-up of Tandem Pump pressure upon cranking. Engine start is now achieved in 530 ms (1/2 a second).
Below we have an overview of the fuel pressure circuits from ignition on (priming), cranking, start up, idling, and finally shutdown at ignition off.

After fix overview

After fix overview

 

 

 

 

 

 

The following waveform revealed an unexpected scenario where the priming pressure at ignition on is equal to the return pressure. Notice also a slight increase in the Tandem Pump pressure that is also equal to priming and return pressures during the ignition off decay period.

Slight increase in Tandem Pump delivery pressure

Slight increase in Tandem Pump delivery pressure

 

 

 

 

 

 

Whilst we had the luxury here to use numerous pressure transducers, had only one been available (as in the real world) we would have used a trigger at ignition on whilst measuring each pressure point individually. Saving each capture as a reference waveform we could then overlay each waveform to arrive at the same conclusion, assuming we keep the time frame and operational conditions identical.

Conclusion

The starting issues that were present from purchase in the summer to mid-winter have now been resolved after replacing the injector O-ring seals. The seals would appear to have leaked (internally) high pressure diesel supplied by the Tandem Pump, preventing adequate engine start. Prolonged cranking would eventually build the Tandem Pump delivery pressure to a point where the engine would start.

The owner had also reported a marked increase in the engine oil level, possibly as a result of contamination from diesel fuel leaking via the high pressure circuit, past the injector, into the combustion chamber and past the piston rings into the sump pan.

Since repair the vehicle has been used daily for over a month and covered numerous miles with no repeat issues and no increase in the engine oil level.

Workshop repair: NVH cabin vibration

By Steve Smith

It is difficult to visualise electricity or vibration as we tend to only experience the effects of both. We sense heat as a result of current flowing through a heating element or we feel tremors as a result of vibration applied to a component. In order to measure and display the energy responsible for these effects we can apply PicoScope.

There are two major skills to using PicoScope, capturing the data (scope settings etc.) and the analysis of that captured data. Vibration analysis is no different but while it can be a difficult concept to grasp, it is no different to measuring voltage in a circuit. We apply the relevant probe and settings to measure the effects of an energy we can feel. For most, Pico automotive vibration diagnosis is still in its infancy but the more I use the NVH kit and review the results, the more I seem to discover.

What follows is a case study from a Maserati Quattroporte that both Stuart White and I had the pleasure to diagnose and, more importantly, rectify. Stuart, who owns and runs Complete Car Maintenance (CCM) in Surrey, had mentioned a customer complaint of vibration on the vehicle around 1,600 rpm when stationary and moving.

The challenge with vibrations is that we all interpret them differently (which is why we should measure and not guess), but with this vehicle, you could not deny a considerable vibration throughout in a very specific engine speed range. Starting at 1,450 rpm through to 1,700 rpm the vibration was evident, with peak vibration occurring around 1,600 rpm. Setting up the PicoDiagnostics NVH kit, we could measure the frequency and amplitude of a vibration relatively easy by following the setup wizard within the NVH software.

Obtaining engine speed is the corner stone of any vibration analysis as the engine forms the source from which we calculate all vibrations. The frequency of all rotating components on our vehicle can be calculated once we know engine speed, transmission/differential ratios and wheel/ tyre size.

In this scenario, we have a vibration from the engine when stationary, so engine speed fed into the NVH software via our ELM lead was sufficient to evaluate vibrations attributed to the engine only. The ELM lead uses the J2534 protocol to request VIN, engine and road speed data via the OBD socket.

Fig1The accelerometer was initially attached to the RH flitch panel (engine bay) as this would appear to be the area of concern given the drivers position in this RHD vehicle. Very quickly, our vibration frequency and amplitude were displayed revealing an uncharacteristic peak vibration of over 116 mg at 40.38 Hz (remember RPM/60 = HZ).

The position of this vibration fell directly at ‘engine order’ E1.5 (1.5 times engine speed).

 

 

 

Frequency chart below indicates high amplitude of vibration at 1.5 x engine speed:
Fig2

 

 

 

To explain engine vibration orders, think about a four-stroke four cylinder engine. Firstly, all vibration orders are measured in the unit of ‘g’ (acceleration due to gravity). The levels we are looking at occur at amplitudes of mg (millli-g), at various speeds expressed in Hz.

E1 (first order engine vibration) is simply engine speed, expressed in Hz (E1 x 60 = RPM). E1 vibrations can be attributed to components related to engine speed such as flywheel and pulleys.

Generally, E2 (second order engine vibration) occurs at twice engine speed and will be the highest level of vibration (for a 4-cylinder engine) given we have two combustion events for every revolution of the crankshaft (two shocks applied to the crank), generating a characteristic high E2. E2 vibration levels can be attributed to combustion events or components rotating at twice engine speed.

On a 6 cylinder engine E3 (and not E2) would be highest, and on an 8 cylinder, similarly E4 would be highest, as should be the case with our Maserati. High vibration levels detected at E0.5 can be attributed to half engine speed components, such as camshafts and associated auxiliaries. Going back to our Maserati, what components could be responsible for our uncharacteristic E1.5 vibration and how could we locate the source? From the above information, high E1.5 orders are typically going to be associated with 3 cylinder engines, yet here we have a V8!

The bar graph below indicates the high level of E1.5 vibration with the included help file:
Fig3

Before diving in headfirst, we must never overlook the basic inspection. Engine oil and coolant level were confirmed correct; whilst hoses, brackets, harness routing and engine mounts were all checked for security, interference or fouling with the chassis.

Cylinder compressions, balance and emissions were also confirmed to be in order and the serpentine drive belt removed to eliminate any auxiliary drive components. With the vibration still evident, this was getting serious! Now it was time to evaluate the schematics of our engine and discover what components were rotating at 1.5 times engine speed.

Fig4Close inspection of the timing gear/chains arrangement revealed an elaborate engine oil pump drive assembly. The oil pump is located remote from the timing gears (rear right of the engine), but connected via a hexagonal driveshaft. Looking at the relationship between the oil pump drive gear to crankshaft timing gear we have a simple 1:1 drive ratio. Such a ratio should produce fundamental engine vibrations in the first engine order (E1) but could also produce other vibrations (harmonics) depending upon wear to the oil pump drive and components. Think of E1 and E2 in our 4-cylinder engines: E1 is the fundamental vibration, E2 is a harmonic of E1 as a result of combustion shocks induced into the crankshaft at engine speed.

Oil pump drive arrangement

So how can we confirm this area of the engine before committing to a repair? The simple answer is we can’t. We can, however, search around the engine for areas of intense vibration (here we switch to using the accelerometer like a stethoscope).

Fig5To generate a vibration we need a vibrating force such as the engine, a transmission path such as the exhaust, and a vibrating element such as the vehicle body. Make no mistake here; we are in for a big repair bill for this vehicle. Any diagnostic results we obtain that help to convince both Stuart and I that this engine has to be dismantled is welcomed with open arms.

Remember, it is better to take advantage of the fact we have the fault to play with as diagnosis is to be carried out before disassembly. Once the engine is dismantled we are on our own as reproducing this fault is then impossible.

Recording vibration levels (amplitude) before and after repair in identical locations will provide far more objective test results than using our senses alone as we all interpret vibration differently.

We know our vibrating force is within the engine and the most likely transmission path is the exhaust. Careful positioning of the accelerometer quickly revealed the maximum amplitude of our E1.5 vibration at the lower right side exhaust mounting bracket, which secures the exhaust system to the transmission.

When we consider the seating position of the driver who complained about the vibration (this is a right-hand drive vehicle), and we now know the engine oil pump speed and its location in relation to the transmission path. We can see a pattern forming…even mounting the accelerometer on the left side flitch panel produced lower vibration levels than the right-side flitch panel. The real beauty of the Pico NVH kit here is that we can take very quick and accurate vibration measurements without making assumptions.

Comparison testing is invaluable when evaluating any vehicle during diagnosis. Using PicoScope we can now test and measure vehicles in a way the manufacturer never intended. By this, I mean we have a dynamic insight into component operation and behavioural functions that we simply have no technical data in which to confirm our results. For example, how many manufacturers quote vibration levels of their vehicles at varying engine and road speeds? Luckily for us, Stuart had been able to confirm a donor Maserati displayed a characteristic cabin vibration at identical engine speeds, but at an acceptable level consistent with this style of performance engine.

So, where do we focus our attention when attempting to reduce this vibration level? The body is our vibrating element but we simply cannot quench the floor pan etc. to improve the vibration. The exhaust is our transmission path but it is simply transmitting the excessive vibration originating from the engine. We therefore have to tackle the vibrating source (the engine) which has to be best practice in this scenario as catastrophic damage could be ahead if ignored.

To summarise what we know:

Time to strip down

Armed with all the above, we had enough evidence to request removal of the sump pan in order to reveal the components attached to the cylinder block, the oil pump in particular. With the sump pan removed, no further vibration measurements could be taken, highlighting the importance of all the actions carried out prior to this commitment.

Fig6

The oil pump/drive was removed to enable access and inspection of all visible components in the crankcase ensuring good security (bolt check) and no visible interference/witness markings. All were OK.

Given E1.5 was our vibration of concern, the oil pump was then dismantled and measured for wear between: pump housing and driven rotordrive and driven rotor and driven rotor side clearance. Whilst some evidence of scoring was visible to the pump housing, all measurements were correct (no real surprise here given that the engine had not suffered any oil pressure related issues).

Fig7Fig8

 

 

 

 

 

 

Fig9

Fig10

 

 

 

 

 

With no faults allocated to the pump assembly, our attention shifted towards the hexagonal pump drive. Looking at the locating points at either end of the hexagonal drive we can clearly see the witness markings on the drive face as a result of drive thrust from the timing gear and pump opposition (load) during the generation of oil pressure.
Both these forces oppose one another, ultimately resulting in the rotation of the oil pump drive rotor and pressurisation of the engine oil. Offering the hexagonal drive into the drive rotor, revealed excessive free rotation (backlash) before any transfer of drive to the drive rotor. Witness markings to the drive face at either end of our hexagonal drive indicate varying size contact areas between the drive rotor and timing gear, suggesting both wear and deformation in the hexagonal drive.

A straight edge and feeler gauge were applied to the hexagonal drive to highlight any distortion and returned a value of 0.076 mm towards the oil pump drive rotor (no specifications exist for this measurement).

So here we now have a decision to make surrounding what components to replace based upon our visual inspection, vibration test results and measurements taken. At the centre of all this information we have the vibration evident at 1.5 x engine speed (E1.5).

We know a crankshaft imbalance would display a first order engine vibration (E1) and our crankshaft is subjected to a fourth order engine vibration (E4) as a result of combustion (4 x power strokes per rev) neither of these is relevant in our test results.

The oil pump drive rotor will rotate at engine speed (1:1 ratio with the crankshaft) but is subjected to 6 x pulses applied as a result of oil compression between the drive and driven rotor. This would be a sixth order engine vibration (E6) and one which is simply not evident. Could the loading of the oil pump upon the hexagonal drive with a partially worn/distorted hex drive produce an E1.5 vibration?

Oil pump and drive load (from the engine) applied to the hex drive, which has good face contact, would produce little or no vibration, whilst load applied to a worn hex drive face has the potential to generate noise/vibration (remember noise and vibration are one and the same).

fig11fig12

 

 

 

 

fig13

 

 

 

 

 

Based on the cost of repair to replace the oil pump, hexagonal drive and timing gear, the customer authorised the replacement of the oil pump and hexagonal drive only. To include the timing gear would dramatically increase labour costs as a result of timing chain removal.

Upon reassembly it became immediately apparent there was minimal rotation (backlash) between the hexagonal drive and oil pump drive rotor, resulting in an instant transfer of drive to the oil pump. The engine was reassembled and the accelerometer placed in the identical position to measure the vibration level at 1,600 rpm.

fig14fig15

Immediately, the vibration level at 1,600 rpm throughout the vehicle had improved (not completely removed) and the values obtained speak volumes, 113 mg before fix and 6 mg after fix.

A combination of wear to the hexagonal drive face, backlash between the hexagonal drive and oil pump drive rotor and the alignment of the hexagonal drive between the timing gear and drive rotor all contributed to the excessive E1.5 engine order vibration.

It is worth noting here, throughout the evaluation of our vibration, we were able to eliminate numerous engine components based upon their respective vibrational frequencies. We were looking for a component responsible for an E1.5 vibration order from a list of engine components however, these components were all rotating at other frequencies.

With hindsight, it would have been fantastic to analyse the fluctuations in engine oil pressure using the WPS500X pressure transducer before and after fix. Could it have been possible to see fluctuations in oil pressure at 1,600 rpm as a result of the wear in our oil pump drive? I guess we will never know but worth considering now we have PicoScope and all these new measurement techniques at our disposal.

Once again, it is invaluable to not only prove what is vibrating, but to rapidly prove what is not.

Objective results before and after fix have proved invaluable as a characteristic engine vibration remained evident at 1,600 rpm but much improved and backed up with undeniable evidence presented by our NVH kit confirming the repair. A big thank you to Stuart White at CCM for his assistance and support throughout this challenging and rewarding case study.

https://www.picoauto.com/library

Video: Testing a coil-on-plug system

How to test a 4-wire coil on plug (COP) ignition system on a Toyota Yaris

(Duration 7mins)