WG start then stall ?? faulty lift pump

[JimmyJ]

Here we go again with gremlins in the WG.

This has probably been on here before but I haven't been able to find it

The car will fire then cuts out after a few seconds. I can get it restarted, but it takes a bit of cranking and then drives fine until turned off and left for more than 10 minutes.

I can see air in the line between the low and high-pressure fuel pump for a minute or so when I get it restarted. The lines were all replaced about 55,000 k's ago as was the fuel filter set up to "something less troublesome" as per the mechanics words. The high-pressure pump was rebuilt and the injectors were replaced at the same time.

I've put a new filter on it but no joy. The local mechanic has just visited and says he thinks the lift pump is the problem. Does anyone have any experience with these failing?

[Adrian D]

It's worth checking if you have a knicked o-ring. It's not unusual.

[JeanLuke]

I had similar. It was the o-ring on the suction side of the lift pump. The lift pump themselves are rarely a problem.

[JimmyJ]

Thanks for the replies.

Yes, I had heard that they rarely went as well. I think I'll try replacing the O rings first even though they're no that old.

Just in case, is the lift pump something that can just be replaced or does it need any software tweeking to match the car?

Cheers

[Deezelweazel]

Check the color of the o-rings:
If they are black-which is the standard color even on new fuel lines, then they are NBR O-rings.
You need to change them into the green ones which are made of FKM(Viton).
Mercedes did the change when they found out Nitril butyl rubber is not bio Diesel resistent.

An anti drain back valve prevent the the back flow trough the supply line to the tank. Helps a lot with the start. Usually your symptom appears when you have already some air in the fuel filter.

Fresh fuel hose (Bio Diesel resistent?) and constant tension hose clamps mounted?

[JimmyJ]

Thank you for your reply. They are the black ones, I'll look for the green ones.
Also funny you mention the fuel filter. I did think the hose on the back of it was the problem as I could feel a little bit of air there and thought that was the whole problem so replaced the filter, cut the end off the hose and put a new clamp on it. But clearly not the whole issue.
Thanks again

[Deezelweazel]

After installing the new engine I added an pre-filter with a very high filtration to protect the expensive injectors and high pressure pump.
It turned out the lift pump was not providing enough fuel during start-up and there was a lot air inside the fuel lines, no matter what kind of changes I performed.
So I added an extra e-fuel pump right behind the fuel tank.
Since that the engine runs smoothly.