G80 Implausible Signal (AEL)

Hi everyone,
This forum looks great! There's a lot of useful and interesting information about VW engines, which is exactly what I was looking for.
I am Italian and I don't speak German, so I will try to explain my problem in English.

I have an Audi A6 TDI 2500cc (1995 - AEL), but the engine doesn't work well: it sometimes makes small "jumps" ("sussulti" in Italian) or a sequence of them under all conditions or at all RPMs. This makes my car undriveable .
The ECU (using VCDS) reports:

Quote:

00542 - Needle lift Sensor (G80) 27-10 - Implausible Signal - Intermittent

I checked the G80 cable, cleaned the N108 sensor, and checked for air bubbles in the fuel system... but nothing has changed.

"I've connected a small switch that allows me to disconnect G80 (from the compartment) when the engine starts 'jumping'. In practice, this forces the emergency program. When I disable G80, the start-stop system activates (although the performance is naturally poor), but sometimes, even at idle speed, the engine still 'misses' some cycles."

Please help me, I'm losing my motivation and passion!

Sure, here's the translation:

"Thanks in advance" translates to "Thank you in advance."
Laurento.

Hi Laurento,

Do you know the "needle lift sensor" check?

Start the engine and let it idle (hopefully it will do so without any unexpected "jerks").
EDIT: not idling, but running at 3000 rpm.

Then take a screwdriver or hammer shaft and hit the sensor nozzle with the shaft.
If the sensor itself is damaged, you should be able to trigger the "sussulti" effect with these impacts.
This means you will have to replace the nozzle.

I'm a little bit confused about that:
The "sussulti" without a connected G80. This contradicts the existence of a broken G80.

Regards,
m;

Hi Laurento,

You need to check the needle lift sensor itself. Measure the resistance at the connector and post the value.
You can also try this: have someone hold the engine RPM at approximately 3000 RPM, then use a screwdriver to tap the needle lift sensor; the needle lift sensor is located inside the nozzle holder, along with the cable.
If the engine stalls, you will need a new nozzle holder that includes a needle lift sensor (as they are integrated into a single part).
Please check the sensor's connection cable and the connection plugs.

Best regards,
Rainer

dieselmartin wrote:

I'm a little bit confused about that: The "sussulti" without a connected G80. This is in contradiction to a broken G80.

I'm confusing about it too .

Thank you for the quick responses.

I measured the resistance of the G80 (a few months ago), and it was within the expected range (I don't remember the exact value, but I think it was around 98-100 ohms). I'll re-measure it and post the result here to be sure.

I'll try the "skrewdriver" test this weekend... I'm not at home right now.

Many, many thanks for your interest. I will post the results of the measurements and the test this weekend.

Meanwhile, I am reading your wonderful scientific papers .

Cheers,
Laurento.

The resistance when the engine is warm (around 90°C) is equal to 119 ohms (I recall that when it's cold, the resistance is approximately 98-100 ohms).

I tried hitting the G80 button, but nothing happened.

I also remembered that when the engine "jumps" or misfires, the ignition timing reported by VAG-COM temporarily increases to 255 (data block 000).