E30 Fuel Pump

[6670charger]

Having an issue with the fuel pump in my 88 325ic. The pump isn't working because there is a short somewhere; the fuse keeps blowing out. It's in the shop right now, but, wondering if anyone else has had this problem and can give me some ideas to pass on to the mechanic that might help speed the process? I've read that there may be two fuel pumps, one internal to the gas tank, and one external? Right now, they're not sure if the short is in the electrical somewhere, or in the pump itself. I'm inclined to believe that it's in the electrical, but I'm no electrical expert.

 

Thanks.

[Boris3]

According to Bentley: "in cold weather, water in the fuel may freeze in the pump, causing the circuit to overload and the fuse [#11] to fail."

Possible?

[B C]

Nice find!
Sounds like a good starting point.

[KaiserRolls]

Could always put an additive in the fuel that has isopropyl alcohol in it.

[jc43089]

Isoheet, ftw in these cold temps.  I put a bottle in with each fillup when it is this cold out.  It's only about 2.79 usually.

[6670charger]

I'll have to check tomorrow. The car has been inside all weekend, so it'll be interesting to see if it starts. Kept blowing the fuze every time they checked it last Friday, and I think it was inside all day at that point.

 

Thanks for the info!

[Boris3]

If it doesn't, try the easy stuff first: change the fuel pump relay and check the connection plug at the fuel pump.

[6670charger]

Could a bad relay cause the fuse to blow?

[jc43089]

Not likely, usually a failed relay won't close (connect the circuit) meaning no current flow.  Too much current is why a fuse blows, either pump is shorted causing high current or a wire is shorted to the body.  The resistance of the pump and its wiring can be measured from the relay socket, I will go measure mine tomorrow unless someone can get it sooner, then your shop will at least know what it should be.  From a quick search it appears that only early e30's had dual pumps, and the late ones like yours and mine have just one in the tank.  Somebody chime in if I am wrong.

 

[Boris3]

Don't know. Short somehow? I've seen bad or loose relays cause all sorts of running/starting issues with e30s. Anyway, easy enough to check and rule out. That and fuse 11 are always the starting points for fuel supply issues.

[Boris3]

Couple threads for ideas:

Wiring issues

http://www.r3vlimited.com/board/showthread.php?t=258998

http://www.e30tech.com/forum/showthread.php?t=104196

Clogged fuel filter issue

http://forums.bimmerforums.com/forum/showthread.php?1884741-What-can-cause-fuel-pump-fuse-to-blow

[jc43089]

I just checked on my 7/88 325i and the resistance from the relay socket on pin 87 to body ground was 1.5 ohms.  This should be measuring through the pump and back through the body, if the value is lower then more current will flow.  12V / 1.5ohms = 8A, this would seem about right, is it a 10A fuse?  Definitely check for sort circuits in the places mentioned in the linked threads.  Very easy to have damaged insulation on a 25 year old car.  Mine has an orange relay BTW.  Hope this helps, let me know if there is anything else I can check.

[6670charger]

Just got the word from the shop. It was the pump shorting out. Oh well. Was hoping to avoid a $350 bill, but, I guess I can't dodge all of those bullets. Have done so with every other one so far.

 

Thanks for all of the info folks! I'll hold onto it for future reference.

 

Eric

[jc43089]

Good deal, glad it's figured out, at least the pump is accessible under the back seat rather than having to drop the whole tank.

[Boris3]

Good to hear they pinned it down. Any sense of why the pump was shorting out and where exactly the short was?

[6670charger]

Good to hear they pinned it down. Any sense of why the pump was shorting out and where exactly the short was?

 

Yes. Turns out that at some point, don't know who, where, or when, the bottom of the gas tank got dented at a point directly in line with the pump. This resulted in the strainer getting broken off, and over time, the pump must have sucked up some dirt or gunk in the tank which overloaded it and caused it to short out.