A4 B6 2.5 TDI: Running Rough - Troubleshooting

Hello everyone,

The car had been parked in the yard for a quarter of a year due to accident damage. I've now started the repairs. The entire front end needs to be replaced, including the crossmember, radiator, etc. During disassembly, I noticed that the "indicators" (I'm not sure what else to call them) on the tensioner pulley for the pump's drive belt were not aligned. I loosened the nut on the tensioner pulley and realigned the "indicators" using a hexagonal wrench, then tightened the nut.
Okay, I started the car, and it's running quite unevenly and also smoking a bit when I accelerate.
After loosening the tensioner, it relaxed, and the indicator needles moved far apart, making the belt quite loose. However, I can hardly imagine that it jumped off. Now, the belt is actually properly tensioned.
Then I wanted to check the injection timing, and I discovered that the crankshaft position sensor is likely defective (it's shorted to ground, so the injection timing isn't being displayed -_-.
I disconnected the hub, but there's no change. Could it be a problem with the hub itself? I've driven before with the hub disconnected, and it worked normally then. It seems like it's relatively unimportant whether the hub is connected or not, especially on the 2.5 models...

Let's assume the belt has jumped a tooth; wouldn't that shift the injection timing so drastically that the engine wouldn't even start?

Hi,
The fuel injection system of the BAU engine only functions with the signal from the needle lift sensor.
Whether there is a short circuit to the positive terminal or not, the motor runs in emergency mode.
hg
Herbert.

Oh, I'm so silly, it's a BDH. As I mentioned, it worked without any problems when the hub adapter was connected.

The fuel injection system of the BDH engine works the same way as the BAU engine.
hg
Herbert.

When was the last time the engine ran smoothly?

Is it possible to identify which cylinder is not firing?

That was before the accident. I checked it again today. I let it run for 20 minutes, and it was better afterward. Let's see how it runs when it's roadworthy again.

When I hear about a type of engine, I immediately think of the camshafts...

They look very good, at least they did six months ago when I replaced the nozzles .