AFN Issue: Troubleshooting and Solutions

My Audi A4 AFN has been acting up since its turbocharger failure last week.
'Occasionally, when starting, the engine doesn't run smoothly, as if it's only running on three cylinders, and it produces black/blue smoke. Sometimes, however, it starts up normally. The outside temperature doesn't seem to affect it. When it's running on only three cylinders, the engine rocks back and forth for about 30 seconds before it starts running normally again after I give it some gas. The last time this happened, the check engine light came on. The error code in the diagnostic memory indicated that the engine control unit was incorrectly coded. I then re-coded it using VAG-COM (00002), and since then, there have been no more errors in the memory. When I start the engine and it runs normally, it produces blue smoke, but only when I give it a little gas; there's no smoke visible above approximately 2500 RPM.'

What could be the reason for that?
The fuel filter has been in use for approximately 5000 miles.
LMM is new.
Injectors have been replaced, mileage is 20,000 km.
The valve timing has been checked and is perfectly accurate.

relay 109? (I think it's called 214 in the A4).
'Install the control unit yourself?'
or are the connecting rods bent again, like with the last charger failure?
By the way, he hasn't used any oil at all for the last 1000 kilometers.

I hope you can help me.

Thank you.

Hi,

Did you perform a compression test?

Best regards, Rainer.

Yes, I did it.
cylinder 1-3, 23 bar.
cylinder 4, 24 bar.

My Audi A4 AFN has been making strange noises since its turbocharger failure last week.
Occasionally, when starting the engine, it doesn't run smoothly, as if it's only running on three cylinders, and it produces black/blue smoke. Sometimes, however, it starts up and runs normally. The outside temperature doesn't seem to affect this.
...

What is the background of the charger damage?

What broke, and how? Also, what was checked and/or replaced?

yes, I did it.
cylinder 1-3, 23 bar.
cylinder 4, 24 bar

That's already below the wear limit! (Experts, please correct me if I'm wrong.)

In my opinion, the target range is 26-32 bar.

Does it still start easily without a lot of fuss?

Next question: Is the compression tester a cheap piece of junk, or something decent?



Beim Billig-Schätzeisen kannst Du nun Schätzen, ob Dein Motor fertig ist oder das Schätzeisen dem Lebenszyklus vieler aktueller Produkte angepasst ist: 1.Kaufen, 2. Wefling

Best regards, Rainer.

It starts without any unusual noises, the key turns, and it runs.

The testing device is from Motometer, so it's a decent brand.

This morning, I experienced the same symptom again, and then suddenly the oil pressure warning light came on, and I discovered a huge oil leak under the car – the oil filter had burst.

I suspect the overpressure valve in the oil pump is faulty, and the oil pressure is much too high. When it runs on only 3 cylinders, it pushes the hydraulic components. I also believe my last two turbo failures (one with two bent connecting rods) are due to the same issue.

Is there any truth to that?
Has anyone experienced something like this before?
'Where exactly is the valve located? Is it sold separately, or only as part of the pump?'

Hello,
Can the oil pressure become so high that the filter bursts?
Best regards,
Günther.

Yes, that is possible. We had a case where the filter didn't burst, but at least the rubber sealing ring came off. Then the oil spreads in the terrain.

Is the valve located in the oil pump?

Wow, that's really intense. I've never experienced anything like it happening.
Most of the time, the oil pressure is too low.
If I had paid attention in school, I would know that the oil pressure in the oil filter is limited.
through a bypass valve. At around 5 bar.
Unfortunately, I don't know if the pressure is currently being regulated by the filter.
I can't imagine that the pump would have any issues with that.
Do you have a way to measure the oil pressure?

There is another valve besides the one in the oil filter that limits the oil pressure.
It's usually located in the oil pump, but I'm not entirely sure about the 1.9 TDI.
'I could measure the oil pressure, but there's not a drop of oil left in the engine, and I'm pretty sure it's coming from somewhere. Otherwise, I wouldn't know why the oil pressure would be so high.'

If I had paid attention in school, I would know that the oil pressure in the oil filter is limited.
through a bypass valve. At around 5 bar.


While that is correct, it only works if the filter is the problem (i.e., if it's clogged).
The oil bypass valve cannot prevent excessively high system pressure. It only bypasses the oil filter, ensuring that the engine receives at least unfiltered oil in an emergency.

As far as I can recall, the pressure regulating valve in the VAG engine is directly mounted to the oil pump, and the oil pump needs to be removed.

Don't forget to check the oil-water heat exchanger.

CU.

Just wanted to quickly say that my car is running again. The piston in the oil pressure relief valve was stuck, so I installed a new oil pump yesterday. The oil pressure is back to normal, and it starts up normally again without smoking. Hopefully, it will run for a while without any problems now.