TD4 Fueling compensation values

Whistler · Apr 20, 2017

Can anyone explain, or point me to a link where I can find a good explanation, of what these are, what they mean and what I should expect to see on my TD4 ? I can read these live values on my diag reader (Foxwell) and even though I have no fault codes coming up, I suspect a problem as the values are all over the place (large variations on individual injectors on tickover, and large variations across all injectors). I'd like to understand it better.
In terms of how the car runs, it smokes on cold start up and runs a bit rough, but once warmed up produces no visible smoke (when running or on start up) and was squeaky clean according to the MOT tester.

Nodge68 · Apr 20, 2017

Compensation is applied to injectors to maintain even fuel delivery at idle. Once the engine is about 1500 or so Rpm, compensation is no longer applied. The figures are derived from those input when the engine was first calibrated. When the injectors are new. They will have a calibration figure attached to them. This figure will be entered into the ECM. The ECM is then able to drive the injectors for the correct time, to give perfect fueling. As the injectors wear or get contaminated, there spec drifts slightly. The ECM is able to detect this drift, and apply a compensation to maintain perfect fueling.
I don't know what the BMW out of spec figures would be. But most common rail engines will have compensation figures of up to 1.200mm3/s across the injectors. Very low or very high numbers signify a problem with that injector.
That's the basic idea of compensation. It's less important at higher Rpm, because actual fuel volume is so much higher, the slight imbalance becomes undetectable.

Whistler · Apr 24, 2017

Thanks Nodge, that was concise and understandable ! A couple of my injectors are showing over 23, the other two are showing around 8 - 10. So they are all getting a bit passed it by the sounds of things.

Madmustang · Apr 25, 2017

Nodge68 said:
Compensation is applied to injectors to maintain even fuel delivery at idle. Once the engine is about 1500 or so Rpm, compensation is no longer applied. The figures are derived from those input when the engine was first calibrated. When the injectors are new. They will have a calibration figure attached to them. This figure will be entered into the ECM. The ECM is then able to drive the injectors for the correct time, to give perfect fueling. As the injectors wear or get contaminated, there spec drifts slightly. The ECM is able to detect this drift, and apply a compensation to maintain perfect fueling.
I don't know what the BMW out of spec figures would be. But most common rail engines will have compensation figures of up to 1.200mm3/s across the injectors. Very low or very high numbers signify a problem with that injector.
That's the basic idea of compensation. It's less important at higher Rpm, because actual fuel volume is so much higher, the slight imbalance becomes undetectable.

How come you know so much about Engines Nodge out of interest

Nodge68 · Apr 25, 2017

Madmustang said:
How come you know so much about Engines Nodge out of interest

20+ year's in the industry. Both professionally and as a hobby.

TD4 Fueling compensation values

Whistler

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Nodge68

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Whistler

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Madmustang

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Nodge68

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