Electrical issues fuel pump - BMW Forum - BimmerWerkz.com
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#1 (permalink) Old 10-21-2007, 12:06 PM
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Electrical issues fuel pump

This is the story, issues might be related, maybe not so I'm looking for a hand here. The cars a 1994 525i w/203,000 MILES. No upgrades full stock oem.

Wednesday took home a miter table closed trunk lid and it wouldn't close shifted cargo and tried again. closed.

Next day morning drive to work no rear window defrosters. Light on at the switch but window never cleared. Got to work and looked in the trunk and saw I'd cut at least one wire in the loom going up along the trunks left side and into trunk lid. After worked stripped soldered and taped wire that was broken. wrapped all wires that looked to have been nicked. I figured I'd wait till the next morning to try rear defrost to see if it worked. Since I couldn't feel heat on the glass.

Next day drove to work no frost so I didn't try. Went to leave work and the car started and then died. First time in 9 years and 150k. to leave me stranded. The car was cranking just fine so went back and grabbed some starting fluid and she fired up but died. So now I know its not getting fuel but why.

I garb my Bentley and look for the trouble shoot for fuel pumps. I look in the engine compartment and find what I believe is the fuel pump relay. As I jump across with my fussed jumper the fuse blows. I try again (Jumping terminals 30and 87) fuse blows. Fuse 23 for the fuel pump is fine by the way. I think that maybe I have the wrong relay out because its a 5 prong and not 4 like the book shows. I see in the fuse box more relays and give it a try there. Now three fuses blown.

I take the stuff out of the trunk and disconnect the wires going to the pump figuring possible locked rotor. Try again jumping the terminals at the relay 87 and 30 in both the fuse box (blown fuse) and Ebox (blown again.)

I now Sunday have a electrical meter and found that when I pin test 87 to 30 meter shows 12v. 3O to ground show 12v. From 87 there is varied resistance to ground. There seems to be a 30 and 87 under every relay in the car. and they all are showing the same thing.

Also the key is out of the car and so I'm checking with the ingnition off.

I now take all the covers out of the trunk compartment and I am looking for a way for the cut and fixed wires from the days before contact the pump. It looks like there isn't a way. The wires from the pump seem to be between the underside of the trunk and tank and re-enter the car near the battery under the rear seat. So I'm not thinking one has to do with the other. But they might.

While I've got the rear seat out and looking over the extra fuses and relays I see that the 30amp for the rear window defroster was melted not really blown like from a dead short. So I replace it. One pin (with fuse out) showed 12v and the other open and also open to ground. The fuse did not blow on contact, but I have not tried the switch.

What I'd like to know is where is the relay I should be checking?
Since I get the 12v to the terminal 30 at most places I check and there is a terminal 87, why then am I reading a path to ground on all of them and not just the pump relay. Where should I be looking? Should I be looking for some cut in the wires where they might be touching? Am I missing some thing? Is there anyway to isolate the different electrical areas to narrow the places for a short. I know the pumps been disconnected so it isn't there. I'd like to find a plug in for the loom but can't find one. Maybe this is bigger then the fuel pump and I'm looking in the wrong area? Are there other electronics that could cause this everything seems to be okay, radio, lights, instruments, no check engine, etc.

I am not the greatest electrical guy but I can follow instructions well enough.

Looks like I'll be riding the HD to work until I figure this one out or may have to get it towed in to a shop. Which I'd rather not do.
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#2 (permalink) Old 10-21-2007, 12:56 PM
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Pictures of issues

Hey I can take and send picture of what it all looks like maybe someone could also send pic back showing where I should be testing. The manual shows the plug going to the pump as male mine is female with male terminals at the pump itself. I took out another relay from the Ebox and its a four prong and I'm going to check again but this one didn't seem to have power at the 30 pin like the rest or like the book says.
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#3 (permalink) Old 10-21-2007, 06:47 PM
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Okay I tossed out the book. I am going to go with a new pump I put all the relays back and left the pump unplugged. With the key forward I had 12v at pin 5 and 4. 12v from 5 to ground. Pump still wasn't running so I'm going to order pump Monday from Bav Auto. If anyone would still like to comment I would be great full. I will post with what I find.
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#4 (permalink) Old 10-21-2007, 09:36 PM
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not sure which pin #s are which without looking but if you check on the 2 pins that are the thickest wire that should be power and ground to your fuel pump. Put a meter between the 2 and you should have 12 volts. this will check both your power and your ground. Ground side is commonly overlooked. if you have them both and the pump isnt running then you know the pump is faulty. You can also try smacking the top of the pump with the handle of a hammer while cranking it over and sometimes the car will start. This is another "shade tree" test.

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#5 (permalink) Old 10-23-2007, 08:25 AM
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Thanks for replying. I have the mentioned 12v at the plug, in my haste originally checking for power I didn't leave the key forward and not seeing 12v I just jumped into the Bentley started to follow what they said the test was. I didn't get power then because the fuse on the jumper was blown. Besides I doubt I had the correct relay jumped. Parts are ordered and should be here Thursday. tried the tapping with a hammer w/o luck.
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