Car stalled twice this morning

[Bob Albrecht]

My Mercedes 350SD stalled twice this morning.

It re-started but is acting like it is out of fuel. The fuel gauge shows 1/3 tank, so I know it has fuel.

I looked at the primary fuel filter and it is about 1/2 full of air, which is unusual.

The engine has been running rough at idle as if it is being starved of fuel. The idle only gets rough when the RPMs drop to about 500. I replaced the fuel filters thinking that might be the problem, but the rough idle persisted. When I filled the tank with fuel the idle was not as rough.

When I replaced the primary fuel filter (the inline one) the fuel flowed very freely, so I don't expect that the screen in the tank is blocked.

Now that the engine has stalled twice I suspect that the problem is a failed or failing fuel lift pump.

Is the best way to diagnose this to connect the fuel intake to another source of fuel?

Does anyone have experience with this and do the symptoms match a problem with the lift pump?

The lift pump looks like it is easy to replace, but expensive. Is there a way to rebuild it?

[SD Blue]

I'm wondering if a clogged fuel tank vent would cause this. An easy way to verify this would be to temporarily remove the fuel cap.

http://www.startekinfo.com/StarTek/outside/12253/program/Engine/602_603/47-030.pdf

[Bob Albrecht]

I was going to try removing the fuel cap. I hope it allows me to limp home.

[DieselJim]

A clogged fuel tank vent can cause this kind of thing. Learned that lesson with my first Mercedes diesel. Lots of towing and headaches I could have fixed if I knew what I knew now. Don't know if that platform vents in a similar way to the w126 but if it does then yes. And from your post I'm assuming you changed both filters. And I do think it might be worth while to change the inline screen especially if you see evidence of diesel algae and preferrably kill/clean the tank

[redoubthill]

First thing to do is to make absolutely sure you do not have any air leaks in the fuel suction line.
Possible other causes are many, here are a few:

1. Low Fuel Level ....you added some though
2. Bad Lift Pump
3. Clogged fuel tank screen
4. Collapsed or kinked fuel hose
5. Deteriorated fuel hose, inner layer
6. Injector carbon build-up (especially if you drive short distances)

This is what I would check first.

Good luck.

[Bob Albrecht]

When I replaced the primary filter it was pretty dirty, but it had been a long time.

The fuel flowed out of the filter pretty fast when I was changing it, but the car had not been running for a while. Usually there is some pressure in the tank, but vacuum would cause fuel starvation.

This all started happening right after I drove over some very bumpy ice in my driveway which made me think it washed some junk off the side of the fuel tank and clogged the filter.

But, changing the filters didn't really help.

[redoubthill]

I realize many people run basically whatever they think will compression combust as a fuel. Before I purchased my wagon, one of the first questions I asked was :

"Has there been anything else besides diesel burned in this car?"

The answer being no, the 250,000 mile plus 617 with almost zero blow-by was purchased. From this, it is my assumption that the minimum blow-by is attributed to burning nothing but diesel fuel as per design.

Point being, that if you have burned anything but real diesel, I am not surprised with fuel related issues. One has to wonder, at least I do; why burning fuel other than real diesel, different fuel line composition hoses are recommended if not necessary.

I'm no expert, but...."If it ain't broke, don't fix it"

[Bob Albrecht]

Originally Posted by redoubthill

"Has there been anything else besides diesel burned in this car?"

I'm no expert, but....

My fuel lines have been replaced with Viton.

Being an expert on the subject, diesel engines run better on biodiesel as long it is commercial-grade. Fuel tanks stay cleaner with biodiesel, but putting biodiesel into a dirty dino tank will cause crud to be removed from the walls of the tank and deposited in the fuel filter.

My car has been running on dino diesel only for about 25,000 miles due to a lack of availability of supiorior fuel.

[GTStinger]

Experiencing similar problems, I cut the tank vent line, blew carb cleaner through it in both directions, then spliced the cut ends back together.

[Bob Albrecht]

If it is the tank vent line will leaving the cap off help?

[Maxbumpo]

Originally Posted by Bob Albrecht

If it is the tank vent line will leaving the cap off help?

Yes, improved idle / driving should be immediate, if the tank vent is the culprit.

[DieselJim]

If its the tank vent you will likely hear/feel the vacuum resistance being broken when loosening the cap

[Bob Albrecht]

It wasn't the tank vent. I drove with the cap off and it stalled once on the way home. Got worse as I went.

When I looked again at the primary fuel filter it had mostly air in it. Obviously the engine is being starved.

It doesn't act like the tank is out of fuel. When that happens there is nothing you can do to start it.

If it were the lift pump, why would there be air in the primary filter before the pump?

Could there be an air leak without a fuel leak?

[ah-kay]

Originally Posted by Bob Albrecht

Could there be an air leak without a fuel leak?

Yes. The lift pump is more powerful than you think. It will suck air around the hose clips if the tank screen is clogged. If you see a lot of air in the primary ( small ) filter then it is sucking air from somewhere.

You can do 2 tests.

1) Rev the eengine and watch the primary filter. Check whether you see any air bubbles entering the filter? If you do then it is an air leak, may be caused by a clogged tank filter.
2) Feed the primary filter with a small fuel bottle and by-pass everything behind it. If the car runs well then the problem is from the tank to the filter. Make sure the return line also goes to the bottle.

Hope this help.

[t walgamuth]

It is not clear from your posts when you changed your filters. If it has been a while I'd check that primary filter again.

I'd also do a biocide treatment on the tank in case there is bacteria clogging the strainer. If there is the biocide will kill it and render it small enough to not clog your filters.

If you ran over ice you could have pinched a metal fuel line so you can examine the line for that too.