My 1987 740 GLE Wagon has let me down twice now and I need some help. It has shut off twice now while driving and refuses to restart. Spraying fuel in the throttle body will restart. The first time it had about a quarter of a tank of gas and when I added a couple gallons it fired right up and I have been driving ii for about two weeks. Today it shut down again with a half tank of gas but would not restart after adding additional fuel. According to the FAQ's this is somewhat of a symptom of a fuel pump that is about to go out. However, before going through all of the bother to change it out I would like to be sure I'm fixing the right thing. Please let me know if you have any info regarding fuel pumps! Thanks! Thom

Hmm.. the rubber hose on my '84 760 Turbo's intank pump had a hole in it a few months ago. When I got around 1/4 of a tank the car would stumble and want to quit but never actually died. Your hose could have a bigger hole, though. Is your main pump noisy when the car is running? They usually get loud when they suck air. Does adding fuel ALWAYS make the car start? It would be nice to know if the power supply to the main pump is cutting out when it dies.

Good luck with it.
Dave

Turn the key to the "run" position. You should be able to hear the "buzz" of the fuel pumps running for about a second, then stop. I have always been able to hear this from the driver's seat, but to be really sure, you could get your ear near the main pump under the rear seat, driver's side (in North America). If you don't hear the pump, then something is wrong with your fuel system, but it's more likely to be your fuel pump relay than the pump itself.
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Andy in St. Paul. '89 244 160K mi, '91 745 209K, '91 745 213K

Would the relay act intermittently like it is doing?

A fuel pump relay vill cause the car to die when it's been running for a while and not restart until it's cooled down some. Remove the hose off the fuel pressure regulator and have someone start the car while you hold your thumb over the nipple on the regulator. If it blows your thumb off the nipple than the fule volume is ok. I'd also want to see what the fuel pressure is with the car running and if it stays up when turned off. The pressue should stay around 30 PSI both running and after sitting.

This EXACT same thing happen on my 87 740 turned out to be the in tank hose that connects the in-tank fuel pump to the metal fuel line there is a piece that is a rubber hose and that broke and after the fuel would get underneath that it would suck in air. you can fix this without removing the tank and there is an acess door behind the rear seats.
If by adding fuel to the car it will start then i'd very much suspect this hose.
You can also remove the fuel line off of the fuel rail and in mine the fuel came out in spurts and not very much while cranking.

Ps: i ran without the in tank pump for years till i fixed it and it made no dif.

Thanks for the tip. I'm about to try that. I did the jumper test across the relay and couldn't hear either the pre-pump or the main pump running. I put the relay back in and it started. I'm concerned it may be coincidental. I don't trust driving it until I find the problem. Even running I can't hear the pump(s) working. I pulled the pre-pump fuse and that didn't change the noise in the tank. Thanks for the input!

TOok the line off in front of the filter (in front of main pump) and fuel flowed out when engine was cranked, but did not appear to be under much pressure, if any. I would have expescted it to spurt out. Is that normal??

If your car has 120-150 k miles, do the fuel pump, it is a wear item. With the main pump OK your car should be running, and you buy yorself time to work out the behaviour of the innards of your fuel tank as per FAQs. Keeping the tank level from running too low is not a big deal, and as said by someone else here the tank assy can be taken out without taking out the tank.

The FPR is the other main culprit to suspect here, it is also very easy to swap with another car, like the fuel relay, which you seem to have excluded with your tests (?).

The car actually has 280,000 miles. I am real close to just replacing both fuel pumps and the relay, but was hoping to isolate the problem. I took the fuel line off in front of the filter (new) and cranked the car. Fuel flowed out but it did not appear to be under much pressure as I thought it should be?????
I am going to test the fuel coming from the tank pump also.