Passat 3B V6: No Power? Fix with LOGs!

Hi,

"I'm experiencing performance issues with my Passat 3B V6 2.5 AFB (1999, 195,000 km). About 5,000 km ago, I replaced the mass airflow sensor (MAF) suspecting it was causing the problem (new part from VW), and I initially saw a significant improvement in performance."

Now I've done some reading in this forum and performed diagnostic tests using VAGCOM.

I logged MWB 010 and 008, and then also 003 and 011. I hope that I carried out the processing as described in the "Instructions."

Here are the data (an Excel table): /download.php?id=2458

My guess is that the problem is again with the mass airflow sensor; the values seem too low.

If that's true, why did this part fail so quickly? I replaced the air filter at the same time, and there are no signs of any leaks in the intake system.

"Errors are not being saved, however, I occasionally encounter the following error:"

01318 - Control unit for fuel injection pump (J399)
49-00 - No communication.

But really only sometimes. This error did not occur during the entire test drive.

"Additionally, I'm experiencing the following phenomenon: When accelerating to maximum speed, it cuts out around 185 km/h. The already low power then drops sharply again, and the engine starts sputtering. The speed also decreases."

Thank you in advance.

Bernd.

Hi Bernd,

To me, it seems like there's a lack of boost pressure. The actual value never exceeds 1600 millibars.

Possible cause.

- Stuck or clogged control valve (possibly try swapping it with the one from the EGR system).
- turbo defect (unlikely)
- vtg adjustment fixed.
- loose hose.


Have fun searching!

Rainer.

Thank you for your reply.

I had the mass airflow sensor replaced (which was still covered by the warranty for spare parts), but it didn't make much of a difference.

I'll try out your tips in the next few days and get back to you later.

Bernd.

As I understand it, you're running in a "limp mode," meaning the fuel injection is being reduced. This can have many potential causes.
Please log the intake air temperature, VGT control signals, etc., and post them. Look at similar cases in this forum to see which logs you need.
Check if your air filter and intake system are okay. You're getting a very low airflow. Mine already reaches almost 700 (units), yours is just under 600. Since the mass airflow sensor has already been replaced, there must be another problem.
If you can't find anything else, remember that the catalytic converter or exhaust system might be clogged. Also, check the camshafts; if they are worn to the point where the valve timing is significantly off, it won't get enough air. Start by checking the camshafts (you should be able to see them by looking down the oil filler neck – that will give you a good initial look). Then, create and post the logs.

Good luck!

Thank you for your detailed response. Unfortunately, I haven't had much time this week. I hope I can find some time next week to work through your suggestions.

I will probably start by temporarily sealing the EGR valve with a piece of metal.

I'll get back to you later.

And thank you in advance.

Bernd.