I purchased a 1976 300d that was converted to a veggie car. The previous owners completely destroyed the car with this conversion. After (my mechanic) replaced the entire fuel system, lines, injection pump, filters, etc & cleaning the tank, sensor & sending unit, the car will stop running if the fuel goes below 1/4 tank (however, if I am driving in an area with hills, it stops at 1/2 tank). After the car dies, I bleed the injectors to get the air out and she runs until the fuel gets low again.

Because my mechanic has checked everything with the fuel system and can find nothing wrong, he does not want to keep searching to fix the problem. He seems to think there is a secondary fuel pump or auxiliary pump, but cannot find enough information on it.

Any thoughts as to what the problem might be? does the car, in fact, have a secondary or auxiliary pump?

I have a 75 300D W115. There is no aux pump. The fuel from the tank is pretty much gravity fed. If everything has been replaced and cleaned then there should be no blockage.

Make sure the return line and the feed line at the tank have not been switched around. That could easily happen. That is the only thing I can think of besides a blockage at the tank or venting problem with the cap.

Good luck,

__________________
Western NC
1987 300SDL W126 Turbo Diesel 335,000 + miles
1976 300D W115 275,000 miles+

I think the hypothesis that the feed and return lines have been switched is a very good one and completely explains the problem.

However, there is a lift pump on the side of the injection pump which delivers fuel from the tank to the injection pump. It's not gravity fed.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Hope I wasn't confusing. I was just referring to the fact that there is no aux pump at the tank and that the fuel will gravity feed out of the tank. Yes there is a lift pump on the injection pump.

__________________
Western NC
1987 300SDL W126 Turbo Diesel 335,000 + miles
1976 300D W115 275,000 miles+

def. check the lines; maybe you can swap them in the engine bay to see if that's the problem

Great! Thanks so much for your suggestions. I will def try swapping the lines. If that doesn't work, I'll try the lift pump.

I really appreciate the help!

One option would be to by-pass the fuel tank and see how it runs. I would also check the strainer on the fuel tank and run the compress are on the lines if not done recently. I had a radiator shop clean out a tank for my 76 300D and there was still a lot of loose stuff that clogged the filters after I got it back

Sal
76 300D
85300D