Audi A4 B6 1.9tdi avant - Loss of power

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Sun 26 Oct 2014 01:40
Audi A4 B6 1.9tdi avant - Loss of power - Audibus
Hi, I'm looking for some advice as i've just bought a 2004 (54) A4 avant and on the way home it suddenly lost power and then the engine management light came on so I pulled over and turned it off. A couple minutes later, started driving and it was fine for 30 secs then lost power again. Whilst waiting for RAC I was advised by someone to remove the pipe from the actuator and try it again. I took it up the road and it went fine and when I put the pipe back on, I noticed a split in that pipe. When the RAC arrived they said it was throwing up codes for EGR valve and turbo (turbo over boost) but couldn't say exactly what the cause was. He sorted the split pipe, cleared the codes and it revved fine until I drove it, it then limited at 3k but no eml this time. Seller and paperwork suggest it had a new turbo 1000 miles ago and then I drive it 60miles (sensibly) and this happens. Any idea what the problem is? Any help will be greatly appreciated as this is supposed to be my work car. Thanks in advance.
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Sun 26 Oct 2014 10:26
Audi A4 B6 1.9tdi avant - Loss of power - dieselnut

The overboost fault code is usually a problem with the turbo vanes sticking, which doesn't fit in with the turbo having been replaced recently.

Perhaps they fitted a secondhand one that hadn't been refurbished properly.

You really need to get it to a VW Independant or someone with VCDS who can investigate further.

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Sun 26 Oct 2014 12:15
Audi A4 B6 1.9tdi avant - Loss of power - Railroad.
I have VCDS, and I'm in Hampshire if that's any use to you. You can check turbo boost expected values and actual values with it. Same for airflow and EGR. The inlet manifold could probably do with a thorough clean too. That's a messy and time consuming job but you can bet your life it's clogged up with thick sludge downstream of the EGR valve.
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Sun 26 Oct 2014 16:36
Audi A4 B6 1.9tdi avant - Loss of power - Audibus
Thanks for the offer but I'm be Exeter and don't want to drive it anywhere. I'll try find somewhere local, I can think of a couple places. Does it have to be vcds or would a snap on diagnostics do? I don't know a huge amount about this sort if thing and I haven't got unlimited funds. Thanks again, for advice and opinions.
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Sun 26 Oct 2014 16:32
Audi A4 B6 1.9tdi avant - Loss of power - Audibus
Apparently it was the cartridge that was replaced, not the whole turbo if that makes sense? If you pull the pipe off the actuator, everything seems fine and the engine/turbo sounds sweet until you put the pipe back on, . The rod does move when you connect/disconnect the pipe, could that mean it's something wrong with the boost valve? Also, EGR code is showing as P0401.
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Sun 26 Oct 2014 18:27
Audi A4 B6 1.9tdi avant - Loss of power - Railroad.
The EGR valve is vacuum operated by the N18 solenoid which is switched by the ECU. When the valve is closed air can only be drawn via the air intake which is measured by the MAF sensor. When the valve opens exhaust gas is drawn, and the ECU sees a reduction in mass air flow. This is how the ECU knows the EGR valve has actually opened when it's switched the N18 on. A fault code willbe generated if this reduction in air flow doesn't happen. The ECU doesn't have any other way of knowing. To understand engine management systems you need to think like a computer. They cannot think or reason. They do exactly what they're programmed to do, and nothing more and nothing less. A loss of airflow would also be caused by sticking turbo vanes. Also check thoroughly for any vacuum leaks and perished hoses.
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Sun 26 Oct 2014 18:51
Audi A4 B6 1.9tdi avant - Loss of power - Audibus
A mate had a brief look earlier and when he disconnected the maf, it made no difference at all. What I don't understand is why it runs fine when the actuator pipe it removed but sounds and runs awful when reconnected?!? It's all a bit beyond me tbh, I don't know a lot about engines or computers so engine management is best left to someone else. I'm getting it checked out tomorrow as I do know it's not as simple as-it's doing "this" so change "that". I just hope it doesn't just become a massive ball ache and money pit.
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