VW T4 Diesel: Starting Problems & Troubleshooting

First of all, belated Merry Christmas .

My T4 is having trouble starting.
Engine: 2.4L naturally aspirated diesel, model AAB.
120,000 km, 78 hp, immobilizer.

The glow plugs (and the fuse) were replaced and are working. The fuel injection timing was checked and adjusted by a workshop. The diesel filter has also already been replaced. All of this without success .

In the morning, I have to crank it for a while before it starts, and it sputters when it does. When it's warm, it starts immediately if it's only been off for a short time.
It's also strange that: Even when it's warm, if it sits for half an hour, it still takes 3-5 engine revolutions to start.

Otherwise, the engine runs completely normally, sounds healthy, uses very little oil, and has full power.

My suspicion:
'While the engine is idle, diesel fuel flows back into the tank. When starting, the engine needs to draw diesel fuel from the tank first. Could it be that air is being drawn in through the actuation shaft of the injection pump while the engine is idling? Isn't there some kind of anti-return valve installed on the diesel filter?'

Could it be that the electromagnetic shut-off valve is sometimes stuck? Unfortunately, I can't easily access it because there's a black cover over it, and the pipes are in the way. (I think this might be related to the immobilizer system).

I am grateful for any advice!

Regards,
Jürgen.

My suspicion:
During the idle time, the diesel fuel flows back into the tank. When starting the engine, diesel fuel must first be drawn from the tank.


Have the oil feed lines been replaced yet?



Unfortunately, I can't access it easily because there's a black cover over it... (I think it has something to do with the immobilizer).


Okay, that's part of the WFS.

Deleted upon request.

Hello,
First of all, thank you very much for the answers!

I would like to temporarily connect a power supply to the electromagnetic shut-off device. This way, I can rule out a fault in the immobilizer, right?
Can I remove the black cover?

I'm not familiar with the tip about the return hoses, but I'll try it out on Monday. They don't actually look very good anymore...

I've also noticed that the area around the injection timing rotor (where you adjust the RPM) is a bit oily. Can diesel leak out from a faulty injection timing rotor, or can air be sucked in? I once had a diesel leak at the injection timing rotor on my T3. I then got a new bushing, seal, and O-ring from the Bosch service, and that fixed it. But my engine didn't have any starting problems then, whereas my T4 does .

Best regards from the snow-covered Allgäu region.

Jürgen.

Hello,
I would like to temporarily connect a power supply to the electromagnetic starter. This way, I can rule out a fault in the immobilizer, right?
Can I remove the black cover?



As far as I know, it's not that simple; it requires drilling.

But first, try to find the problem in the fuel system.
I don't believe the error is due to the WFS at the moment.

Deleted upon request.

Hello,

Sorry for the late reply, but I've solved the problem now.
Thank you everyone for the helpful answers!

I replaced the fuel lines to the injectors, the diesel filter, and the associated valve. Now the fuel flows through the lines without air bubbles, and the engine starts immediately every time. However, I don't know exactly what the problem was, since I replaced everything at the same time. But it doesn't really matter.

Positive side effect: My auxiliary heater is working again now!!!

Regards,
Jürgen.