No power to fuel pump

e34west · 15th May 2012, 18:22

Hi guys,

I have a 1991 Euro M5 that is giving me some fuel pump issues. The car is new to me and over the winter I had done some freshening up... vacuum lines, coil, cap, rotor, plugs, new battery and so on. Car ran fine when I parked it in the fall, but now when I go to crank it, the pump is not pumping any fuel. I jumped the relay and tested the plug that goes to the FP, and there's no power. I tried doing the same thing on my 525i, and it works fine.

One concern I have is that the car has an aftermarket alarm. I'm wondering that when I changed the battery, it may have affected the alarm's functions. Is it possible that even when jumping the relay, the alarm could be affecting the fuel pump?

Additional info... I have the 5 prong fuel pump relay. Swapped in the orange 4 prong from my 525i and no difference. Fuel pump is new. Fuse is good.

Thanks in advance...

e34west · 16th May 2012, 16:52

Any thoughts guys? How could the fuel pump not be getting any power when jumped? Is the fuel pump relay in the same location as a non-M5 e34? I'm looking at the middle of three relays in the E-box.

MattH · 16th May 2012, 17:26

This is a long shot, but do a search for the Alan Archer posts on rear wiring harness issues. On his 3.8 (I note yours is a 3.6 so this harness is probably different) he had an issue where shorts in a worn part of the harness where stretched over the rear subframe caused issues with his EDC. I know because I have the same issue (my speedo is out and I'm pretty sure this is related).

So as I say, a long shot, because I dont know if the harness in 3.6's is prone to a similar failing - but worth searching to see if others have had the issue.

uk_bm · 16th May 2012, 19:55

So far as I can see if the fuse F23 is 12v then the pump should be running.

It it is live then it's just wiring (feed or earth), or the pump.

MY BUD · 16th May 2012, 21:01

Have you tried checking for spark as well as fuel? If you have neither then the crank position sensor could be at fault.

e34west · 16th May 2012, 22:26

Quote:

Originally Posted by uk_bm

So far as I can see if the fuse F23 is 12v then the pump should be running.

It it is live then it's just wiring (feed or earth), or the pump.

Well when I jump the FP relay, there is no power to the fuse. I think I'll have a look around the wiring by the FP. If there is a bad ground back there, then there would be no complete circuit, and no power at the fuse, right?

uk_bm · 17th May 2012, 00:41

You're bridging the relay socket with wire, or something?

Have you checked 12v at the socket? Another thought is that O2 sensor element is playing up and pulling down the voltage. Or no power into the socket etc etc.

e34west · 17th May 2012, 01:14

Yes, bridging with wire. Power at all three sockets. 12 plus volts on each.

uk_bm · 17th May 2012, 15:26

So we seem to be saying there is a break between the socket and fuse.

e34west · 17th May 2012, 17:21

That what it sounds like. What about a bad ground? Could a bad ground in the engine bay affect the FP? I had a lot of stuff apart in there, and maybe something didn't go back together exactly right.