Audi A4 1.9 TDI: Excessive Smoke, Low Boost?

Hello everyone,

I'm having a very serious problem with my Audi A4 1.9 TDI, year 1997 (engine code AFN), 110 horsepower.
As soon as I accelerate or drive at a constant speed on the highway/country road, etc., I experience significant soot emissions (my license plate is no longer visible). This also results in slightly reduced power and slightly higher fuel consumption (0.3-0.5 liters).

I have now logged the values 3.8 and 11, as well as 4.22 and 11 using VAG-COM. However, I'm not sure if these values are incorrect and what the problem might be.

My suspicion is that either the intercooler piping has a leak (oil is leaking near the EGR valve and a sensor on the pressure hose), or...

Adjusted injector due to incorrectly timed timing belt (replaced 10,000 km ago).

It would be great if you could help me!!!!

Best regards,
Eiko

You are approximately 0.2 bar short of the expected pressure at full load. This means you either have a larger leak (not a small one like the one you mentioned with the pressure sensor), a problem with the control system, or an issue with the turbocharger. I assume your engine is not chipped.
"...and please make this table readable for everyone, not just a collection of numbers."

See you later.

As far as I know, the engine hasn't been chipped. Is there a way to check the system for leaks?

How can I check the turbocharger? And could such heavy soot production be caused by 0.2 bar? It's producing a lot of soot even when it's slightly loaded, even at 130 km/h on the highway...

Should I replace the EGR valve, or will that not help?

But thank you very much for the initial help!!

If it's caused by a leak, you'll hear a hissing sound, and there will likely be a significant amount of oil around the leak. It could also be a vacuum hose that's faulty or pinched behind the diesel filter (was a recent inspection done?). It's not easy to diagnose a tuning issue, but since you only have 0.7 bar of boost pressure, it's probably not due to too much diesel. You shouldn't drive like this for too long, as you'll be overstressing your turbocharger, which could quickly break down or spin out of control.

Hello,

Problem solved, it was a faulty turbo hose!
Now I have high charging pressure again, and no excessive, persistent soot.

Is it normal for the turbo to overboost (3rd gear, full throttle) to 2172.6 mbar? It only happened once, otherwise it's usually close to the target value !

Thank you!!

Yes, small pressure surges are normal. Everything needs to stabilize, and eventually the pressure surges shouldn't be larger than 0.2 bar.