Need help tracking down fuel issue

[Konica]

Hey guys - first post and it's a question. Hope that's Kosher here. Been a member on bimmerforums for a bit - but im pretty new to the bmws.


Anyways, I have an 89 535ia.

One day I was driving through the alley and it stalled out. After pushing the car for a bit - I got it started again and drove it into the garage, where it promptly died again and has been sitting since.

-I pulled the fuel line - turned the car over - no pressure, no fuel.
-I replaced the filter - no go.
-I pull the fuel pump - tested it by hooking it right up the battery with alligator clips and firing it for 2 seconds dry. Works fine.

So next I hook the fuel pump back up to the wires, and hook up my multi-meter. When I turn the engine over, I see that the pump is only getting between 1.5v to 4 volts peak. Barely enough to run my keyboard.


So what's wrong here? The relay isn't a likely culprit - they either work or they dont....

[genphreak]

Hey guys - first post and it's a question. Hope that's Kosher here. Been a member on bimmerforums for a bit - but im pretty new to the bmws.


Anyways, I have an 89 535ia.

One day I was driving through the alley and it stalled out. After pushing the car for a bit - I got it started again and drove it into the garage, where it promptly died again and has been sitting since.

-I pulled the fuel line - turned the car over - no pressure, no fuel.
-I replaced the filter - no go.
-I pull the fuel pump - tested it by hooking it right up the battery with alligator clips and firing it for 2 seconds dry. Works fine.

So next I hook the fuel pump back up to the wires, and hook up my multi-meter. When I turn the engine over, I see that the pump is only getting between 1.5v to 4 volts peak. Barely enough to run my keyboard.

So what's wrong here? The relay isn't a likely culprit - they either work or they dont....Do you get power at the FP relay? If not you have to trace further back. Is the fuse perfect?

I'd guess your relay is the problem- but it might be that the FP is absorbing too much current and has caused the relay to overheat in the first place. It might be easiest to re-solder the actual relay terminals on the relay PCB.

[Konica]

I get 11.8 volts at terminal 30 and terminal 86 of the relay SOCKET with the ignition off.

That's all the testing I've done on the socket - and the relay itself, I don't know how to test so I've left it alone.

And fuse 23 for thefuel pump looks OK to me. The metal is has a slight curve - but it's completely 100% attached, and doesn't bear any indications of being blown.


I guess the next step would to be to jumper the relay socket? What pins do I cross on the socket to turn the pump on? That would at least confirm or eliminate the wiring being the problem.

[pingu]

If you unplug the fuel pump relay, then I think that the underside of the relay will show (as a wiring diagram slightly embossed into the relay) which contacts are which. If the relay doesn't have the diagram then you could measure the resistance between the various terminal - when you get something like a hundred ohms then you've got the coil contacts (anything under an ohm or more than a few a few tens of K won't be the coil).

Given that you are getting some volts to the fuel pump, I'd guess that the fuse is OK. Maybe the contacts of the relay have become arced and no longer have a low resistance?

[whiskychaser]

I guess the next step would to be to jumper the relay socket? What pins do I cross on the socket to turn the pump on? That would at least confirm or eliminate the wiring being the problem.
You need pins 30 and 87 and they are shown on the bottom of the relay. With the relay removed, this should correspond to the 'slots' at 9 o'clock and 12 o'clock. I use a split pin as a jumper

[Konica]

Correction -sorry guys.


I jumped 30-87 without the relay plugged in - the pump definitely did not fire.

(with the ignition in, with the ignition out, and while trying to turn over)

[whiskychaser]

Correction -sorry guys.


I jumped 30-87 without the relay plugged in - the pump definitely did not fire.

(with the ignition in, with the ignition out, and while trying to turn over)
The only thing between pin 87 and the pump is fuse 23. Try replacing it with a known good one. If that doesnt work, disconnect at the pump and check you have 12v and a ground. Theory: Pump may work OK dry but when it has work to do it may fail and drag the input voltage down

[Konica]

I took some pictures today because I noticed a few things that may or may not be part of the problem...


I noticed these two slices on the connector in the trunk - they don't seem to have damaged the wire - but I should probably fix this right?

Is there a way to remove the wires without damaging the plug, or is that a waste of time?
http://img208.imageshack.us/img208/2192/img0017mt7.jpg

This is from the left back-set of the car. If you look at the arrow, you'll notice a ground wire missing - should I be re-attaching it? I wasn't able to find the wire itself - but I only looked briefly...
http://img169.imageshack.us/img169/7744/img0012pd4.jpg

[Konica]

bumpity

[whiskychaser]

I took some pictures today because I noticed a few things that may or may not be part of the problem...


I noticed these two slices on the connector in the trunk - they don't seem to have damaged the wire - but I should probably fix this right?

Is there a way to remove the wires without damaging the plug, or is that a waste of time?
http://img208.imageshack.us/img208/2192/img0017mt7.jpg

This is from the left back-set of the car. If you look at the arrow, you'll notice a ground wire missing - should I be re-attaching it? I wasn't able to find the wire itself - but I only looked briefly...
http://img169.imageshack.us/img169/7744/img0012pd4.jpg
Dont know what the spare ground in photo is. Looks like an add-on. But as for the 2 crimped wires, stick pins through the insulation either side of the crimp. Test with DMM. If you have continuity, you have no problem. Patch with insulation tape. (May not work with heavy duty circuits like engine earth lead but for this you should be OK)

[Ross]

That ground wire isn't a part of the factory harness. It's likely from a cell phone.
You said the pump ran when you applied power directly but not when jumping terminals at the relay socket. Either the wiring or fuse to the pump are open or you jumped the wrong terminals.
A relay can have a lot of resistance at the contacts so your assumption that they work or don't isn't quite right.
Swap the relay and see what happens.

[Konica]

Problem solved!

The wire from the fuse to the pump was frayed - I re-soldered the wire - and now I'm getting 11.8-12 volts to the pump.

I jumped the relay socket after re-soldering and the pump ran flawlessly.

Also replaced the relay and the fuse just in case.


Thanks for the help guys!

[calibra]

Problem solved!

The wire from the fuse to the pump was frayed - I re-soldered the wire - and now I'm getting 11.8-12 volts to the pump.

I jumped the relay socket after re-soldering and the pump ran flawlessly.

Also replaced the relay and the fuse just in case.


Thanks for the help guys!

May i ask how easy was it to get the fuse box out?