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Non-intrusive engine testing – By David Wagstaff of Technical Topics

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Back in June, we were pleased to host a very interesting training event here at Technical Topics HQ in Bridgwater. The event was organised by Ryan Colley of Elite Automotive Diagnostics, who had arranged for technical expert Brandon Steckler to fly in from the States to talk about the subject of pressure pulse analysis. 

Brandon’s background is as a Honda dealer technician and his knowledge of pressure pulse analysis came from a personal interest in the subject and the resulting research he undertook. He spoke of spending many hours just staring at waveforms on a computer screen trying to understand what was going on and the relationship between the waveform and gas flow within the engine. His passion for this is obvious as soon as he talks about the subject. 

Although the training was headlined as pressure pulse analysis, it actually covered many aspects of non-intrusive engine condition analysis. He began by starting with using an oscilloscope and an Amps clamp to carry out a relative compression test to look for compression pressure anomalies. This is probably one of the most valuable tests that can be done with an oscilloscope and one that if you are new to scoping, should get to grips with. The process is such a timesaver, allowing a compression test to be carried out in a couple of minutes without the need to remove spark plugs, glow plugs or injectors, and this also avoids the risks of a snapped component. The time saved from this will help to pay for the oscilloscope alone. 

If you have carried out a relative compression test and identified a loss of compression, the next step would be to work out what the cause is. The lost pressure must have gone somewhere. If a valve or the piston rings are not fully sealing, then as the piston moves up the bore, it will push air past them and create a pressure pulse. We can use a pulse sensor such as Pico FirstLook or Autoditex Pressure Pulse Sensor to display a waveform on the oscilloscope screen. These sensors do not measure absolute pressure but instead produce a voltage output as the pressure changes. If the pressure stabilises then the output returns to zero. So, they are measuring change in pressure and not the actual pressure in a system. 

When we carry out a manual cylinder leakage test, we apply pressure to the cylinder from our workshop air supply and listen for the escaping air from the inlet manifold, exhaust or crankcase to tell us where the pressure is leaking from. However, with this test, we crank the engine and use its own generated pressure to find the leak. The pulse sensor is effectively ‘listening’ for the escaping gasses, so we place the sensor in the exhaust, inlet manifold or dipstick tube to trace the fault. 

By adding a cylinder reference, perhaps from an injector or ignition coil, we can even work out which cylinder is at fault, how cool is that? This is completely non-intrusive and within just a few minutes, gives us a firm cause of an internal engine fault. As no mechanical stripping has been undertaken, if the car is beyond economical repair, the customer can drive it away again, meaning no pushing cars out of the workshop with heads removed and being stuck with a disabled car in the car park until the customer decides what they are going to do with it. 

Much more information is contained in the pressure waveforms once you have a good understanding of them. Brandon could, for instance, see issues with valve clearances on a V6 Honda engine by just simply placing a probe into the exhaust on a service and looking at the waveform. If he spotted an issue, he was able to upsell a valve clearance adjustment job, knowing it was required. 

Brandon moved on to talk about in-cylinder pressure waveforms using the Pico WPS500. Although this now involves getting access into the cylinder by removing something like a glow plug or spark plug, it does give us more information about the engine’s mechanical condition. We can now measure actual compression pressure (both cranking and running), see issues with airflow in and out of the cylinder, valve timing and sealing issues, plus any mechanical issues with the valve gear. 

When you get to more complex issues you can combine all the techniques above and display relative compression, in-cylinder pressure and pulse sensor waveforms on the screen together. The information can be overwhelming but there are a few overlay programs that can be used to help work out what is happening in different parts of the screen. 

The event was well received by all those that attended and has created quite a buzz in several online forums. It was so popular that Ryan is likely to invite Brandon back for a second round of training – keep an eye out for more details. 

If you want some more hands-on training, we’ve been running training at Technical Topics covering very similar subject matter for a few years now as part of our ‘Oscilloscope Masterclass’ course. We use our engine test rig to get you deep into engine condition analysis, relative compression tests and pressure waveforms, using both pulse sensors and WPS. We can insert faults on the engine and let you explore the results whilst we guide you, enabling you to build your knowledge of the technique. The next date for this course is Sept 30th, if you’d like more information on the course contents and dates, please check out our website at techtopics.co.uk. 

Finally, I’d like to thank Brandon for his very interesting and informative presentation, Ryan Colley for organising this very enjoyable event and Steve Scott from Simply Diagnostics for his support. 

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