A6 AAT cold start problems, the umpteenth...

Hello community!
Although it's rare thanks to the search function, it does happen occasionally, and I'm stuck. I have a customer with a slowly but surely increasingly acidic issue, and he's having cold start problems with his Audi A6, manufactured in 1997, with approximately 195,000 kilometers on the odometer. If it were a 1Z, I would suspect the well-known crankshaft sprocket based on the symptoms I have also observed, but that is not the case with the AAT.
Here's what has been done so far:
Both timing belts replaced (with timing alignment tool and dial indicator!), ensuring the static timing is precisely set to 0.25mm and the dynamic timing is adjusted and aligned to the center line. Fuel filter replaced.
Here are the measurement values that the measurement blocks in my Gutmann tester are producing:
Start of injection: Actual value matches the target value, no deviation. Maximum correction amount during nozzle comparison: 1.5 mg/hour. However, here's the problem: The pulse width of the injector control valve is around 75%!!! And this is happening even with the injection start precisely set. And if I activate the injector control valve through the actuator diagnosis, then it functions properly.
Question: Where could the dog be buried? Any ideas or suggestions? I'm quite sure, based on the startup behavior, that the problem lies in the late start of the boosting process, but theoretically, it shouldn't be possible due to the settings. Or have I made a mistake somewhere in my thinking?
Regards,
Dominique.

Hi Dominique,

I can't really make much sense of those percentage values right now, just by looking at them.
My suggestion: Keep the pump running in idle mode, without using any initial setting mode. While the engine is running, gradually increase the timing until you hear the engine knocking more noticeably.
At the point where the hammering becomes more pronounced, the pump's injection start setting has reached the end of its adjustment range.
-> Idle should be fine, but the cold start needs to be perfect.

The injection start, ideally around 0° BTDC (+/- 2° BTDC should be acceptable), is okay when the engine is hot and idling. If you don't want to warm up the engine and then have to wait a long time to test the cold start, simply connect a second... Place the temperature sensor in a pot of hot water.

Attention: It's important to replace the oil feed lines. Otherwise, the pump and lines might become empty due to air being drawn in after prolonged periods of inactivity.

Best regards, Rainer.

My AAT (Anti-Aircraft Trigger) only worked correctly when it was set slightly too early, as determined by the multimeter method. It might be a sign of wear and tear on the pump.

Is the evaluation of the start of funding not carried out via the NHG?
Perhaps it sometimes freezes or lags.
Define 'cold start'. Given the current temperatures, it's probably safe to say that the heating system can be completely switched off.

Best regards,

Gottlike wrote:

Is the evaluation of the start of funding not carried out via the NHG? Perhaps it sometimes freezes or lags.

At startup, the internal pressure of the pump is not sufficient.

Hello!
Right, Christians, when starting the engine cold, only the static injection start is relevant; the injection timing adjuster should be in its resting position, which is why I'm even more surprised...

@Gottlike
I define 'cold start' as temperatures around 7-10 degrees Celsius, such as those found in underground garages or the current outdoor temperatures in Central Europe in the early morning. Although I initially disabled the preheating system during troubleshooting, I double-checked it completely just to be sure, and everything is working correctly. It can't be because of that.

Regards,
Dominique.