W124 E300D Air in Fuel Lines

[Mick65]

Hi - over last few months my 96 W124 E300D has started intermittently cutting out usually within a mile of leaving home. It all started after I ran out of fuel once.

When it fails there is no fuel in the fuel lines, just air. Cranking / leaving for a few minutes sees it running again normally without repeat but it often feels a bit flat / stuttery. On one nightmare occasion, it failed every 20 miles or so on what became a 10 hour journey up the M6.

Had car into various independents, an MB specialist and MB main dealer diagnostics. Fuel tank strainer changed, relays checked, vacuum airlines checked. All saying they don't know what the fault is.

Car starts fine. There is air visible in the clear fuel pipes (which various people have said is normal) and a slight fuel leak on the black fuel pipe between the main filter and lift pump. MB specialist told me that it wouldn't be the fuel pipe O-rings as they would also cause starting problems.

Having read various posts on here, I'm not so sure and am thinking that changing the fuel pipe O-rings. replacing flexible pipes and overhauling the fuel lift pump might be worthwhile, and certainly preferable to the main dealer's suggestion of replacing the injector pump.

Does this sound right for the symptoms? Should I be doing / checking anything else?

Where can I get O-rings, flexible pipes and a overhaul kit for the lift pump from?

Thank you for any help & advice. I love my car and just want to get back to being able to use it without worrying every time I go out.

 

[a111r]

See post #20
OM606 starting and running problem - Page 2 - Mercedes-Benz Owners' Forums

I'd start with the O ring behind the valve indicated in blue. The valves can fail internally, too.

 

[bolide]

The only way you can stop an E300 diesel is to shut off the fuel. Ergo, your problem is fuel feed

I take the point that leaky O-rings would cause starting problems but I'd still replace them. They tend to flatten with age and become 0-shaped rather than O. Any time they are disturbed they tend to start letting air in

In my experience the fuel pipes don't leak so I wouldn't bother replacing them. Do all the O-rings, replace the fuel pre-filter and O-ring and replace the fuel filter & O-ring. Do that with the engine hot so you can get it restarted. Then test again

If it's still problematic, check to make sure the fuel shutoff valve is opening fully. The fact that the car dies at motorway speeds suggests lack of fuel flow and a partially-closed shutoff valve will do this

I have heard lots of stories of the lift pump being replaced when there was no need, mainly due to lack of proper diagnostic procedures. But if the shutoff valve is open, the tank strainer has been replaced, all the pipework is OK and there are no air leaks, then you'd have to say that the lift pump might look like a candidate

The lift pump is on the IP so the whole fuel system up to the pump is under vacuum. Any air leaks in this section will see air drawn into the fuel system. I think I'd concentrate on this

Two final things: my local independent had an E300 Diesel that no-one could cure. He replaced the alloy filter housing and the problem went away. It had gone porous.

Second is the manual shutoff valve on top of the filter. They can leak and some continue to leak even with new O-rings. They are a stupid price but can be replaced with the alternative version bolt without a valve

How many miles has the car done?


Nick Froome

 

[219]

All sensible suggestions above .

In my experience , if no one is sure of the cause of a fault , I tend to start with the cheapest things first and go from there . If DIY-ing , these O rings should not be expensive .

 

[Mick65]

Thank you everyone for your help.

Nick - really helpful post. Very grateful for your experience on this - the chap I bought the car from told me you were the W124 expert

Car has done 160,000

Since posting, I turned the fuel-shutoff valve on top of the fuel filter down (my theory being that maybe too much fuel was being returned unused to the tank creating a back pressure) and have had two weeks trouble free running. Sounds like i may have inadvertently hit upon the problem you mentioned with the valve leaking.

Will keep fingers crossed.

If fault returns, which is the fuel shut-off valve that you mentioned earlier that should be checked?