NHG Lag? Troubleshooting and Solutions.

Hello,

Currently, I have two identical cases of older VP37 TDIs that exhibit similar behavior, but don't fit the known patterns.

- In both cases, occasional severe jerking occurs, and the error code "injector control valve implausible" is stored in the memory. The engines are an ALH and an AFN.
- In both cases, replacing the NHG (which I did myself using new parts from Henzo) made absolutely no difference.

The ALH (Air Leakage Hole) tends to rattle more when it's warmer outside, while the AFN (Air Flow Noise) is not affected by temperature. However, the rattling occurs almost reproducibly above 3500 RPM.

Okay, so now the question arises whether this *must* be the NHG (presumably a specific sensor or component). The second parameter (for determining the injection start) would actually have to come from the crankshaft position sensor (or incremental encoder).
The distributor rotor has 4 lobes, and therefore provides 8 pulses per cylinder cycle via the speed sensor.
If, hypothetically, the sensor becomes too slow due to aging and/or heat, or if it stops emitting pulses, the engine control unit (ECU) will consider the measured injection start time to be implausible. This would occur if only 7 crankshaft pulses have been registered by the counter, but the knock signal (NHG) is already present.

What do you think? Does my theory make sense?
I don't want to unnecessarily replace the crankshaft position sensor based on suspicion alone, especially with cars that have a low residual value, where every cent counts.

Hi,

"So far, I've only experienced this described effect with a faulty needle lift generator or its wiring. There's no error that can be detected; everything is fine for days, and then it starts to stutter. Replacing the needle lift generator resolved the issue."
I haven't experienced any failures with the crankshaft position sensors yet, but that doesn't necessarily mean anything.

When performing a full-throttle test, it's important to check whether the desired injection timing can still be adjusted, as this is often no longer possible with higher mileage engines.

Best regards, Rainer.

Quote:

When checking with a full-throttle log, you should verify whether the target injection start can still be adjusted, as this is often no longer possible with higher mileage.

Thank you, Rainer, for figuring that out instead of me .

When the AFN is running at > 3500 RPM and under load, the actual value drops back to 10° vOT after a few seconds, while the target value is 15° vOT. I suspect it's related to the pressure inside the pump, so I will now check the fuel side .

Here's the solution: The return short circuit valve on the fuel filter was permanently short-circuiting the return line, causing fuel temperatures to exceed 100°C. The resulting vapor bubbles caused a drop in pressure inside the pump, and the injector control valve was temporarily in its resting position.
Due to the rapid change in actual value, the control system determined that the injection molding machine was not providing a plausible value.