I am trying to troubleshoot a faulty fuel delivery system on a 1981 240DL.

I was driving the car last week when it just stopped running. No sputtering or anything other than it just came to a stop. I think that I have determined that the fuel delivery system is faulty since when I disconnect the fuel filter (on the firewall) and turn on the ignition no fuel begins to flow.

(By the way. the engine will hit and start when I spray starting fluid into the intake manifold)

I am assuming that when the ignition switch is turned to "ON" (not to "START") the fuel system should try to pressurize and it does not. Therefore I am expecting the problem to be the fuel pump but I would greatly appreciate any assistance I could get on checking any fuel pump relays or electrical circuits which support the pump and the fuel system as well as where to look at the pump. My understanding is that the fuel pump is below the car and I do not hear any sounds when I turn on the key but I still have yet to get it up on the ramps to look at the pump.

I will be doing that this evening or in the morning depending on the help I can get from the forum.

I have a Haynes manual but it comes up a little short in this area.

I have a '86 528e that I have been working on and I think the fuel systems are somewhat similar.

Also, I do not have the fuse "box" cover on the driver side kick panel to identify the fuse layout. I do know that there are ten (10) fuse "slots" on a top and six (6) below a little divider on the pannel. Can someone please help me to identify the location of the fuel system relays or fuses so that I can check that out or point me to a URL that might have it.

Any and all help is greatly appreciated.

Thanks

Rick B.

'81 240DL
'85 528e
'76 Camaro (original owner)

The fuel pumps ONLY run when the relay receives a pulse from the ignition system. When it receives a pulse, the relay kicks in for about 1/2 second, then drops out. Often, but not always, when you turn on the key (not to start), it will create one quick spark pulse -- and you'll hear the pump buzz for a half-second.

Obviously, cranking and running produce a constant stream of pulses, so the relay stays engaged. You MUST have spark in order to have fuel pressure.

You can force the pumps to run by jumping fuse #5 to #7 (#1 is topmost). This will work even with the key off and is a good diagnostic but an unsafe way to drive your car.

Fuse #7 protects both pumps and other FI components (idle air valve, etc.) and fuse #5 provides additional protection to the tank pump.

Your fuel pump relay is under the dash, approximately above the driver's left knee, near the hood release knob. It's usually dark red or dark green.
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Don Foster (near Cape Cod, MA)

You might check the fuses. Fuse no. 5 (8A) powers the prepump and no. 7(16A) powers the main pump. May sure the ends of the fuses haven't oxidized. I have had that happen and the pump ran fine after the fuses were rotated within the holder. Wish you luck.

If your car's layout is remotely similar to my '83's (despite the different fuel systems) then you should be looking under the dash above the passenger footwell for the fuel relay. Problems like this one are caused by the fuel pump relay 90% of the time. Fix or replace it and you should be on the road in no time. The fuel pump goes out over time, and only after making groaning noises for a while.
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Isaac Babcock - '83 245DL and '83 244ti, Peace, love, and all that good stuff