1.9 TDI AVG: Common Problems and Solutions

Hello,

'I have three problems with my Audi A6 1.9 TDI, model 2000, manual transmission (mileage: 170,000 km), which might have related causes. For your information: About 2.5 years ago, someone rear-ended my car quite severely, and as a result, the following parts were replaced:'

- the complete exhaust system.
- Later charge (Kat) due to damaged flexible pipe.
- Approximately 9 months ago, both engine mounts were replaced retroactively due to load-shifting vibrations.

Furthermore, the timing belt was replaced shortly after the repair. All the problems have only occurred since the accident or the timing belt replacement. The vehicle is in its original condition, meaning it has no aftermarket modifications like a chip and the EGR system is functioning correctly. Now, regarding the problems:

1. Problem: 'Rough' or 'Hard' engine running and loud engine noises

Das was mich im Moment am meisten stört, ist der „harte“ Motorlauf. Man kann das schlecht beschreiben, aber man kann den Motor förmlich im Innenraum spüren, besonders am Boden und Gaspedal. Des Weiteren finde ich die Motorengeräusche sehr laut. Wenn ich den Motor starte, habe ich das Gefühl als wenn ich direkt im Motorraum sitzen würde. Im Vergleich zu dem A6 von meinen Eltern mit AFN Motor und den PD TDI von einem Freund, ist die Motorenfrequenz auch viel höher und aufdringlicher, quasi als wenn die Dämmung fehlen würde. Ich habe schon eine zweite Dämm-Matte an die Motorhaube gemacht, leider brachte diese keine Verbesserungen. Besonders extrem wird es ab ca. 3000 Umdrehungen (ca. 160 Km/h) Ab da fängt es richtig an zu brummen und zu dröhnen, das selbst mit lauter Musik zu hören ist. Ab 180 Km/h ist aber wieder ruhe. Gerade auf Langstrecken ist das besonders nervig, da dieses extreme dröhnen im optimalen Reisegeschwindigkeitsbereich auftritt. Sporadisch ist jedoch auch mal ein „weiches“ und fast leises fahren möglich, was aber leider selten ist. Unterschiedlich ist auch das Schütteln beim starten und abstellen des Motors. Manchmal schüttelt sich der Motor fast gar nicht, an anderen Tagen wird man im Auto fast durchgerüttelt. Dies This would, in turn, indicate faulty engine mounts.
'This definitely shouldn't be normal, as it doesn't occur in the vehicles mentioned above. Especially the PD Golf, which is supposed to have a rougher engine sound compared to the VEP TDI, is a true pleasure... and so quiet.'

My initial hope was that replacing the engine mounts would improve the engine's performance and noise, but unfortunately, that wasn't the case. After searching the forum, I found similar problems that were linked to incorrect timing due to the timing belt replacement. However, checking with a TDI timing checker didn't yield any results. The injection timing is actually set optimally, and I'm not experiencing any starting problems. The error memory is empty. Does anyone have any suggestions or possible solutions? I'm really at a loss.

2. Problem: Loss of power, especially in the lower RPM range

'For some time now, I've also been experiencing a loss of power, which is particularly noticeable in the lower RPM range. I've logged data blocks 3, 10, and 11. Perhaps a professional could take a look and draw some conclusions. I've only noticed that the mass airflow value seems a bit low. There are two other things I've observed. The mass airflow value occasionally spiked to around 435 mg/h at idle (but this didn't occur during the logging), which, according to some forum posts, could indicate a problem with the EGR system. Furthermore, during my last inspection, a technician used a diagnostic tool. The expert disconnected and only lightly reconnected the MAF sensor connector. There was an error code present. What's striking is that I couldn't detect any difference in performance. Shouldn't that be noticeable in terms of power?'

And here's the third problem: Jerking when accelerating.

When I accelerate again after being in a low-throttle state, there's always a jolt, and the intensity of the jolt depends on how much I press the accelerator pedal. In a post I found, the EGR valve was also identified as a potential cause. Are there any other possible causes besides that? Perhaps other engine mounting components that could be related to problem number 1?

Okay, that's all for now. It would be great if some of you could offer some suggestions or assistance.

Regards,
Mike.

Hello! This is a really well-started topic with a lot of information, which is rare and great!
Since you have VAG COM, I'm sure you can be helped. I just took a quick look at your log, and at first glance, I didn't see anything particularly noticeable. However, you should try doing a few acceleration cycles with full throttle, perhaps in 3rd gear, and then log the data. You seem to have a lot of idle and partial throttle conditions. The three full-throttle readings look pretty good.
Based on your description, several things seem to point towards an issue with the AGR valve, even though it might not be immediately obvious from the log data. However, I've only taken a quick look. It's possible that your AGR valve isn't closing properly due to its mileage, which could explain the jerking. However, that wouldn't explain the booming sound. If the booming started after the timing belt replacement, the cause is likely there. It's possible that the belt driving the auxiliary components is incorrectly installed (though I'm not sure how that would happen) and is now vibrating at higher RPMs. It's also possible that the tensioner is defective. You mentioned a timing check was okay, which seems good. It's strange that it's happening at the same time. If the booming started immediately after the accident, check if the exhaust system was properly aligned and free of stress; it can definitely cause unpleasant booming sounds.

Okay... I hope I could help you a little bit to start with.

Can you easily access the EGR valve located upstream of the intake manifold on an A6? If so, try removing the intercooler hose and shining a light on it; it might be leaking, and cleaning it (if possible) could improve things.

Hello,

danke für die Antwort. Der zeitliche zusammenhang zwischen Unfall und Zahnriemenwechsel macht die Fehlersuche nicht einfacher, das ist leider richtig. Nach der Reparatur des Unfallschadens war aber noch ein Dröhnen im Leerlauf und beim Anfahren zu hören. Dafür wurde das Flexrohr als Ursache genannt und samt Kat getauscht. Deswegen lässt sich noch schlechter beurteilen, ob dies mit dem Unfall oder Zahnriemenwechsel zusammenhängen kann . Die Abgasanlage wurde von der Werkstatt schon mehrfach in Augenschein genommen und als spannungsfrei beurteilt. Diese lauten Geräusche im höheren Drehzahlbereich würde ich vielleicht eher als Motorbrummen charakterisieren, will aber nicht ausschließen, dass es sich auch um ein Dröhnen der Auspuffanlage handeln kann. Vielleicht hat die Werkstatt ja auch beim Einbau vom Kat geschlampt und das Geräusch kommt daher. Da sich das Flexrohr beim ersten mal auch nur im Leerlauf bzw. im ganz niedrigem Drehzahlbereich bemerkbar gemacht hat (ca. 1000 bis 1400 RPM), hatte ich dies als Ursache nicht in die engere Auswahl genommen. Kann sich ein defektes Flexrohr auch im höheren Drehzahlbereich bemerkbar machen? Wie gesagt, es gibt auch sehr seltene Momente, in dem der Motorlauf weich und leise ist. Unfortunately, these are very rare.

Regarding the log values: The first two full-load measurements were taken in 3rd gear, from 1500 to 4000 RPM, while the last cycle was in 2nd gear, within the same RPM range. The timing check was OK. I've attached a Screenshot. The point fluctuates between the ideal line and the displayed position.

I'm going to temporarily disable the AGR (if I can get the hose off) today and see if anything changes.

Regards,
Mike.

Okay, I temporarily disabled the EGR valve, but absolutely nothing changed. You can't tell any difference at all whether the car is running with or without the EGR valve .

Yesterday, I also went to the to have the issue checked. According to the technician, everything is supposedly okay and completely normal. Normal... so-so. Then I will have to take matters into my own hands, as much as possible.

My gut feeling tells me that something might be wrong with the valve timing, but I lack the knowledge and the tools to check it (setting the crankshaft to top dead center and then checking with a timing tool... that's completely new territory for me. I wouldn't even know where to start).
'The engine is making an unusual knocking sound. Today, I logged data blocks 4, 8, and 10 again. Can anyone tell me if there are any anomalies that can be identified? I suspect that the injection timing is outside of the tolerance range under full load. Can anyone confirm this?'

Thank you for the help .

Regards,
Mike.

What about the turbocharger? Has it been checked?
"In an accident like that, I think a significant force must have acted on the turbocharger, which is directly connected to the exhaust system via the downpipe."
I would like to check if there are any small cracks visible on the exhaust manifolds or on the exhaust side of the turbocharger, and whether the turbocharger is securely attached to the exhaust manifold, and whether the downpipe is firmly connected to the turbocharger.
Otherwise, it's immediately noticeable that your LMM (lambda) values are a bit too low. This could be related to a leak on the intake side or a faulty EGR valve that isn't closing completely. How did you "disable" the EGR for the test? Try using a metal gasket; that will definitely prevent any exhaust gases from entering the combustion chamber.

Hello helmaker,

"The occasional humming and droning noise above 3000 RPM, as well as the unpleasant thud or jerk when accelerating from idle - which becomes more pronounced the more power you demand (gas pedal) - is, in my opinion, 99% related to the engine mounting."
A well-known problem with pillow block bearings is this booming tendency at high speeds, which occurs when the installation guidelines for motor alignment are not followed, or when the supports do not receive new expansion bolts during assembly. The noticeable load impact also indicates a stressed motor mounting.
The fact that there was no change after replacing the engine mounts throws everything into question, and I find it puzzling.

The fuel injection timing is perfect. The turbocharger pressure build-up also looks good. The HFM (likely referring to a sensor) isn't the best anymore, but it's still within acceptable limits. Those few small units that you're missing won't be noticed by anyone.

The fact that the engine performance doesn't change with the EGR system disabled is also fine.

The mentioned lack of torque in the lower RPM range can have multiple causes. Try removing the EGR valve and check your intake manifold for oil deposits. Otherwise, searching online will help you with systematic troubleshooting if you're experiencing a lack of power.

The rough idle and knocking, well, that's of course highly subjective - there are good and less good TDIs in this regard. Wear on the injectors, lack of compression, defective hydraulic lifters, there are many possibilities here. If the mediocre idle quality was already present before the accident, it's usually impossible to pinpoint a specific cause. If the idle stabilization system doesn't show any abnormalities, I would initially ignore it.

In the end, all that might be left is a belt drive that was improperly assembled, or perhaps the exhaust system, but you have to be careful about how much you trust the mechanics' assessments. It could also be a loose piece of metal or something similar.

Ultimately, I can only wish you good luck, and I hope it helps.

Best regards,

Hello everyone,

Thank you for the answers. If all the injection starts are fine, then the workshop may have really cut corners during the installation of the engine mounts, and they might be under tension. I will investigate this further.

After reaching a certain mileage, the vehicle definitely deserves new fuel injectors. This might improve performance, reduce engine knocking, and provide a smoother running experience.

Due to the 'rumbling' and vibrations, I will investigate the engine mounts. If nothing helps, I will probably need to add more soundproofing material so that I don't hear anything anymore . If there is any new information, I will report it.

Best regards,
Mike.