PD and CR Injectors -- Normal Compensation Rates for Reference Comparison

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JMR

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Seeing how many diesel engine users wonder what a good injector compensation rate should look like on a PD / CR injector , here are my happy numbers ( from 0.00 to 0.99 mg/str).
Ideally these compensation rate readings should be done at about 80-90 degrees C warm engine at idle.
Will try to post good injector rates for different engines as I get to them , please keep this post free of replies and just cross reference your injector compensation rates to this post.

Touareg 2007 , 2.5 TDI BPE

https://flic.kr/p/2mRJNsf
 
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dieseldub

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Those numbers are changing all the time. General rule of thumb is it's pretty healthy if no single injector is being told to correct more than 1 mg/str, and even then, generally you aren't going to notice much until maybe closer to a 2 mg/str correction value.

What is less known on PD injectors specifically is they have another measuring value that can tell you a lot about the health of your fuel system or even help track down specific injector problems. Measuring value block 23 (and 24 for those engines with more than 4 cylinders). This is the injector solenoid closing time deviation, also known as the "beginning of injection period" deviation, or BIP for short. Beginning of injection period meaning the moment the computer detects the solenoid has closed fully is the start of the injection period.

PD injectors still "pop" mechanically. All the solenoid is doing is temporarily blocking the fuel's escape path out of the injector and to the return circuit, forcing the pressure to build inside the injector as the plunger is pressed down by the rocker arm operated by the camshaft.

The measurement is in microseconds, I believe? Values that are negative means the solenoids are detected as closing faster than the computer expects, which CAN indicate a fuel pressure problem. I have noticed that a good way to determine if you likely have a clogged fuel filter is to get a baseline of what your engine reads in MVB 23 at idle, then go for a drive. As you press the throttle to wide open while rolling down the road, if the values spike significantly further negative, you have a fuel system restriction. If they stay relatively the same no matter the load, the filter is likely not overloaded.

On the other end of the spectrum, I did have a BEW in the shop once that was setting intermittent injector #2 codes. In MVB 23 I could see that that particular injector was nearing the max number it can register, +125, while most of the rest of the injectors were slightly negative (values ranging from near 0 to -0.25 sort of idea, which is normal). I ohm'd out each injector's solenoid at the wiring harness barrel connector, injector #2 had a reading of about 0.2 ohm higher than what the rest were reading. Since there was some gunk inside that connector housing, I decided to pull the valve cover, remove the plugs from each injector and then measure resistance across each solenoid directly, not just through the harness. Readings were identical and there clearly was increased resistance in that particular injector.

I replaced the injector, started the engine up and re-checked my BIP values. #2 was now in line with the rest of the injectors with a slightly negative reading and the car was happy. Old injector seemingly just had a bad winding or something in the solenoid that was causing it to close slower than the computer wanted to see or otherwise something else that was causing the increased resistance and sluggish solenoid response.
 
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Jef

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Uwe

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2015 NAR Touareg TDI, CNRB Engine, ~97,500 km:

CNRB-Inj-Deviations.png

-Uwe-
 
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