Passat 3bg AVF engine occasionally stalls

Hello everyone!

I've often found helpful tips in this forum, but I'm currently facing a problem that I can't seem to solve, and I'm hoping for some help from you!

The following problem:

Passat PD AVF, 294,000 km.

The car has been running for the past 6 years and 60,000 km without any problems.
Now, for a few weeks, he's been experiencing a problem where the car stalls without warning when he releases the clutch, and it won't restart on its own. However, it can be started again using starting fluid, and then it runs as if nothing happened.
The problem occurs approximately every 100 kilometers.
Once, there was an error code in the fault memory that read "Misfire detected, cylinder 2."
No entries for the other times.

I've also been driving around with VCDS for hours now, checking the data logs, but I haven't found anything unusual.

The only thing that stands out is the idle speed control.
Every time the engine stalls and I restart it, cylinder number 2 always shows a reading of +2.00 mg/h or higher. The other cylinders are operating within the range of +-0.30 to 0.40, while cylinder 4 compensates for the high value of cylinder 2, which is approximately -2.00 mg/h.

However, after about 10 minutes, it stabilizes, and all cylinders operate within the idle speed control range, with a deviation of plus or minus 0.20 to plus or minus 0.40 mg/h! In both cold and warm conditions.

As I mentioned, the issue with cylinder 2 misfiring only occurs after the engine has been turned off and restarted.

Meanwhile, many parts have been replaced, but there has been no improvement.

AGR
PD wiring harness.
Spark plugs.
Diesel filters.
"Snapping turtle"
Freewheeling brassiere.
Timing belt was replaced 20,000 km ago (synchronization at 0.6).

I really hope someone can help me.
I'm going to install four new (remanufactured) power distribution units, although I'm not sure that's where the problem lies, but I'm at a loss for what else to do.

Best regards from Austria.
Oliver.

Hi,

It sounds like the fuel supply to the PPD elements might not be entirely constant, possibly when more power/fuel is required.
If it starts running again and the readings are bad, then you probably have air in the system that will eventually work its way out.
So, the LLR values are back within the acceptable range.

Could you please provide the pre-pressure of the electric [device/system]? Check the fuel pump, then check the pressure of the tandem pump.
If everything else seems to be in order, then one of the PPD elements, likely the O-ring, is probably leaking between the supply line and the return line.

Regards, Mpire.

Thank you for your reply.

I will review the points you mentioned tomorrow.
However, it doesn't shut down under full or partial load, but rather when being switched to a lower power setting.
As soon as the clutch is depressed, the engine stalls.
But I will check the pressure of the two pumps tomorrow.

P.S.: Could it be that the pre-lift pump fails during driving?
Does it then drain the diesel filter until it stops working? Because otherwise, I won't be able to breathe in this system.
explain? Where should he draw the air from? What possibilities would there be for that?
Sure, here's the translation:

"Best regards,"
Oliver.

And if you immediately shift into the next gear, will it work again? Is power available?

Hello!

Engaging the clutch again immediately will not be effective. It doesn't start.
Only spraying starting fluid directly into the intake manifold will get it to start.
After approximately 30 seconds, a loud rumbling sound...

He will regain his performance when he starts running again. Smooth and consistent airflow, no stuttering.
Sure, here's the translation:

"or anything else."

Best regards, Oliver.

Today, on my way home from work, the car stalled again when I was releasing the clutch.
The intervals where this happens seem to be getting shorter.

I definitely tested the tandem pump: It delivers 3.6 bar.
The pre-pump is also working perfectly and is producing a pressure of 1.3-1.4 bar.

Best regards,
Oliver

Did you measure the pressure while the engine was running, or at the moment it stopped and failed to restart, despite the presence of fuel?

Hello!

I checked the tandem pump while the engine was running, using a VW pressure gauge tool.
The pre-charge pump operates when the engine is stationary. I activated the pre-lift pump using VCDS.
I need to check the pump pressure if it doesn't start.
However, I still have to wait for the outage to be resolved. I can fix the error.
Do not reproduce. I was driving around for about 80km earlier and tried out different scenarios.
to simulate (country road, highway, urban traffic). It went without incident.

Okay, try measuring it when it's turned off. In my opinion, the problem lies in the electrical system, either with the pre-feed pump or its power supply.

Okay, I also suspect it's something electrical.
I'm just going to replace the relay for the booster pump now. Are there multiple relays that should be replaced?
Which relays are we talking about? The 109 or something else?

Best regards,
Oliver

Hello,

If it doesn't start, does the preheating light blink?
If it's completely dead, then relay 202 is defective.
It's for the fuel pump and preheating.

Best regards,

I need to pay attention to that.
If the preheating light doesn't blink or is not visible, does that mean the relay is broken? Am I understanding this correctly?

Sure, here's the translation:

"Best regards,"
Oliver.

r28oli wrote:

Today, after work, while driving home, it stalled again when I disengaged the clutch. The intervals where this happens seem to be getting shorter. I definitely tested the tandem pump: It delivers 3.6 bar. The pre-pump is also working perfectly and is producing a pressure of 1.3-1.4 bar. Best regards, Oliver

Just a thought, since you're triggering the error by releasing the clutch.

Check the Multi-Function Display (MWB) to see if the signal from the clutch pedal switch seems reasonable. You might also try wiggling it while testing, and even try it while the pedal is depressed (2nd position). Man) and see if there are any changes in the MWB (presumably referring to a specific system or database).
They are completely made of plastic and can sometimes break, developing hairline cracks, etc.

It might also be worth checking the brake pedal switch, using the same procedure.

Regards, Mpire.

Clutch pedal switch and brake pedal switch tested and OK.
Okay, I just pulled relay 202, and the engine starts and runs perfectly fine, even without the relay.
Then I activated relay 167 for the diesel additive pump, but it still starts and runs???

How can that be?

The next idea I have is: could it be that one of the PDEs sometimes malfunctions and sometimes doesn't?
Could a sticking throttle position sensor (TPS) cause the engine to stall while idling?

Hello,

You should check the relay for the power supply from the engine control unit.

If you pull that, the engine will also turn off.

Best regards, Rainer.

Hello everyone!

Slowly but surely, I'm getting closer to solving the problem.
The engine is drawing the diesel fuel from the fuel filter, but apparently not consistently.
The pre-charge pump measures its target pressure even on the return line to the tank.
I have now replaced the glow plug preheating valve and the diesel filter (genuine VW parts) again, but without success.
Then I replaced all the rubber fuel hoses. I tried blowing air through everything, and nothing was blocked.
Here comes the funny part.
If I close the preheating valve and connect the return hoses in a way that the diesel fuel bypasses the filter and flows directly back into the tank, the diesel filter remains full. The engine does not stall. I've been testing this for several days now.

But now I'm stuck again. Should I replace the tandem pump and pre-charge pump even though I don't have any specific evidence of a problem?
I'm slowly feeling the pressure because I have something due on the 5th. I'm planning a trip to Spain by car in April, and I want to resolve this issue before then.


Edit: Does anyone know the flow rate of the pumps? I'd like to be able to check that. I can't find any numbers about that online!


Hoping for help.
Best regards,
Oliver.