I'm hoping someone out there might be able to offer some help. I have a 1990 740 GLE wagon which I bought with about 91K miles on it a few years ago. It has intermittently had acceleration issues which have now worsened. I noticed that when I let the gas tank run down to about 1/4 I could hear the fuel pump under the drivers seat working erratically. As I result I always tried to keep the tank at least half full.

While driving to get gas one night at about 30-40 MPH the car suddenly had no power...someone else in a post here stated the same problem by saying it was as if the accelerator had been suddenly disconnected. I rolled to the side of the road when it finally stalled. However, it immediately started up again and I was able to get to the gas station, fill up, and get home without further problem.

This same thing has now happened a few times even with a 3/4 to full tank. My mechanic replaced both fuel pumps but I am still having the problem.

The car will also sometimes not start. Usually when I turn the key to "on" I can hear the fuel pump activate. However, I have noticed that on the occasions that it doesn't start, I cannot hear the pump come on. I turn the key on and off a few times until I hear the pump activate and then it turns over just fine.

So, my question is, what might it be that is not telling the fuel pump to come on when the car is started and could this same thing also be telling the pump to quit while the car is moving?

I would greatly appreciate any guidance that anyone might be able to give to me!

 

Change the fuel relay and see,actually you should have done it before changing the fuelpumps.

 

Many thanks! I'll have my mechanic do that if he hasn't already.

 

You could swap out the relay yourself with little difficulty. Instead of throwing new parts on the car hoping to solve the issue, have your mechanic take the time and run some basic "diagnostic" - this word is too often absent when work is done on cars - tests to actually locate the issue.

 

to me, the noise on an low tank, sounds like the smaller fuel pump in the gas tank is dead. I had this same sort of symptoms, car ran 10X better when it was replaced.

but I'm with gabanja... run diagnostics. fuel pump issues show up with a fuel pressure test, which requires a special gauge, but can be done in 5 minutes.

 

Thanks for your input everyone. The tank pump was replaced because he found that the pressure was not good. I hoped that would solve the problem but it did not. It seems as though something is preventing the pumps from running (at start up) and killing them when I am up to speed. Hopefully the fuel pump relay will prove to be the culprit.