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The technology of a GDI injector

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ASNU looks at injector flow rates and spray patterns and we speak to Clive Atthowe Tuning in Norwich, a VW & Audi specialist who has already invested in GDI kit, to see how lucrative the service and repair of GDI injectors is for the independent workshop.

The most important feature of a GDI injector is not the flow rate of the injector but the fuel distribution and atomisation that form the injector’s spray pattern. ASNU has experience of GDI injectors with differences of up to 15% in flow rates between the best and the worst delivering injector, yet the engine still runs without a problem. How is this possible?

Developments in the Engine Management System now allow the flow rate to be automatically adjusted to an individual injector to compensate for any deficiency in the injector’s ability to deliver the correct amount of fuel. In theory this is ideal, in practice, it is not.

This feature is not correcting the problem, it is compensating for it and, although in the short term the vehicle is running fine, in the long term the problem will need to be addressed when the EMS reaches its compensation tolerance level and the engine’s check light comes on.

GUESSWORK OR CORRECT DIAGNOSIS

As the injector’s performance deteriorates and the EMS compensates for the lack of flow, how does it measure and compensate for the changes and deficiencies in the fuel distribution and atomisation?

FACT 1:

If you had six injectors with six different deliveries, with the help of the EMS, the engine would run correctly. With six different spray patterns and six correct deliveries, the engine would run badly.

FACT 2:

If you had six injectors and six different spray patterns, the engine would run badly and the engine check light would illuminate. If not addressed, the EMS would eventually put the engine in ‘Limp Mode’ to protect it from damage.

FACT 3:

The injector’s spray pattern is designed for a very specific delivery angle and fuel droplet size. This ensures the fuel is directed to the correct location in the combustion chamber with a droplet size that will burn efficiently. Any disruption to the distribution or droplet size can and will have an adverse effect on the combustion process in that cylinder.

FACT 4:

The Fuel Trim Compensation for a bad spray pattern is to increase the fuel content. The engine’s EMS sees a weak combustion stroke and believes that it needs more fuel. Usually, it has the correct quantity, it’s just not atomising correctly. The cylinder now has excess fuel that is not only adding to the problem, but creating additional ones in the process.

FACT 5:

Now the cylinder has excess fuel, this can cause carbon build-up on the piston, excess burning on the piston crown, bore wash, gumming, sticking and slow response of any gas recycling valves and components, lacquering of the lambda sensor as well as clogging and damage to the catalytic exhaust.

YOU CAN’T FIX WHAT YOU CAN’T SEE

An EMS cannot analyse the injector’s spray pattern. The spray pattern of a GDI injector is absolutely critical to the correct running, fuel economy and emissions.

There is no way to analyse the injector’s spray pattern while it is still on the engine and the compensation actions of the fuel trim programme is not beneficial for the long-term good of the engine.

“Correct analysis of the injector’s spray pattern is critical to the engine’s long-term performance and should not be considered an option”

ASNU low pressure testing replicates the results of high pressure testing, offering a safe and detailed examination of injector function. To the aftermarket workshop, they are critical to efficiently resolving issues with an engine’s performance, preventing the unnecessary replacement of expensive injectors that may only need servicing.

For more information on ASNU equipment, contact:

Email: 0208 4204 494

Phone: phil@asnu.com

IS GDI SERVICE AND REPAIR A GOOD INVESTMENT?

We ask Clive Atthowe, an independent VW & Audi specialist in Norwich, about his experience of offering this service to the public and trade customers.

“Having the ability to test and prove the injector is faulty is for me a fundamental part of my diagnostic process”

WHEN DID YOU INVEST IN ASNU EQUIPMENT AND WHY?

“I have owned an ASNU Bench for over twenty years, upgrading to the Classic GDI when this became available. The reason for buying ASNU was that I was experiencing running issues on various engines that were found to be caused by injector spray patterns and poor deliveries. I had tried various methods of cleaning, mainly chemical treatments that weren’t very effective, but I still had no means of accurately testing the injector itself. After seeing the ASNU injector bench demonstrated, I knew I had found the equipment I needed.”

HOW OFTEN DO YOU USE THE KIT AND WHAT TYPES OF PROBLEMS HAVE BEEN RECTIFIED USING IT?

“I use the ASNU almost daily nowadays, predominately testing GDI injectors. Running issues and misfires on modern GDI is something we see often, having the ability to test and prove the injector is faulty, is for me a fundamental part of my diagnostic process. We have successfully diagnosed poor spray patterns across the entire RPM range, sticking and locking injectors, intermittent and permanent faults, delivery issues and faulty injector coil windings.”

HOW HAS THE KIT AFFECTED YOUR BUSINESS?

“The ASNU bench has without doubt raised our profile and helped us keep our reputation as an injection specialist. We carry out a lot of testing of injectors for our local trade and this also enables us to establish the other services we provide. Sometimes when we test injectors we find no faults, we can then advise the best course of action for the customer. The equipment also sets us apart from other local diagnostic garages that don’t have an injection bench, this makes it easier to sell ourselves above the opposition. We are an ASNU Injector Service Centre and receive enquiries from all over the UK to test and clean injectors.”

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