Low Fuel Injection: Faulty Control Unit?

Hello,
I have a long-standing problem with insufficient power in my A6 C4 TDI AEL. I've been to numerous workshops. After two of them gave me the same diagnosis: faulty turbocharger and control unit, I had the turbocharger replaced. The workshop wanted to order a replacement control unit on a trial basis, but that never happened. The boost pressure is now back within normal limits, but the power is still lacking.
Can I compensate for the insufficient fuel injection with a 'tuning' that costs only 10 cents? If so, how should I proceed, as described?
Regards,
Martin.

Hello Martin!

Generally, the goal is to restore the vehicle to its correct condition, so avoid unnecessary work if the existing problem hasn't been fixed. Do you know what the workshop meant by "control unit"? Could it be a vacuum system solenoid valve? Or perhaps the EGR valve function? How did you conclude that there's insufficient fuel injection? Has the mass airflow sensor (MAF) been replaced, or has a test drive been conducted to check its functionality? What is your fuel consumption like? Is there excessive soot production? How many kilometers does your A6 have?

Regards, Peter.

A too low fuel injection amount is usually caused by a faulty mass airflow sensor (MAF). The '10-cent tuning' should not be performed until the engine is running perfectly.
Your workshop should install a new MAF sensor for you as a test, and then you'll quickly see the issue with the fuel injection amount.

Hi,
according to mhernach in your last thread https://community.dieselschrauber.org/en/viewtopic.php?t=3568&highlight=lmm+ael
Does the AEL have an air flow meter? Like the one on my AAT, with a spring-loaded flap and potentiometer.
It is nowhere near as prone to failure as the mass airflow sensors in newer engines.
Otherwise, please refer to what has already been written there.

The engine control unit (ECU) is supposedly defective, which is why it's injecting too little fuel. This is the second workshop that has confirmed this. The repair is estimated to cost €1700. The mass airflow sensor (MAF) has already been replaced and a test drive was performed, but it's still within the acceptable range.
It runs normally, doesn't make excessive noise, and has low fuel consumption, but it just lacks power. I was thinking of increasing the injection amount with a '10 cent' tuning modification, which should be possible for testing purposes.
Regards,
Martin.

Hello,

Okay, then I'd rather build a fuel economy adapter first and check what error codes are stored in the engine control unit, how much fuel is being injected, etc.
If you want to spend 1700 flakes based on a hunch, go ahead. I don't believe in that control unit.
What makes the workshops so confident in their diagnoses?

Best regards, Rainer.

The workshop isn't 100% certain either. However, this is the fourth workshop I've taken it to for a diagnosis, and the second one that has identified the same cause.

hello,
I just spoke with my mechanic again, and they said there might be another cause: the fuel injection pump's quantity adjuster. However, it's not available as a separate part; you have to replace the entire fuel injection pump.
Has anyone had experience with this before? Has anyone dealt with something like this? Is it possible to repair this?
Regards,
Martin.

Hello Martin,

"Faulty quantity adjuster" is unfortunately just as vague as the content of the previous posts.
A vague error description can only elicit a vague response: perhaps a repair is possible.
Without details and measurements regarding your problem, further discussion is pointless. Because in that way, nothing meaningful can come out of it. A (incomplete) replication of the opinions of others is unhelpful.
The topic will therefore be locked.

My advice to you: Go to a Bosch service center. They are usually more knowledgeable than VW/Audi authorized workshops and should also have the necessary diagnostic equipment. I would keep the previous diagnoses to myself when placing the order.

Best regards, Rainer.