Fuel pump won't shut off

[joammo]

New to the forum, hope to get some answers and contribute when I can! I picked up an 86 325es the other day for 500 bucks and have been trying to make it run. Right now I am dealing with two problems. One, the fuel pump does not ever shut off, even if all the relays are pulled (meaning the three by the air box). the other problems is no spark from the coil but I'm getting ready to swap CPS so I'll work that later. Any ideas on the pump thing? The car has gas, the regulator is working (at least no fuel is coming out the vacuum side) and the pump is running fine, it just won't stop.

Thanks,
Wendell

[riceh8r]

someone has done some electrical work for you. maybe bad cps and they were trying to bypass stuff to get it to run. they couldn't get the spark...and sold it. search for an electronic troubleshooting manual for the specific model you have. you will need it more in the future. good luck.

[joammo]

Yippee!! How fun is that gonna be? Well I already replaced the entire engine harness so I guess they jacked around under the dash somewhere and hot wired the pumps to be on at all times. Time to get with the PO and see WTF he/she did! I downloaded the ETM already, I hate electrical problems. I will let you know what I find....

[Sagaris]

I haven't discovered what signals the fuel pump on BMW's with motronic yet but I know that the Toyotas I have worked on that had a vane airflow meter would begin running the fuel pump when the AFM flap moved. Make sure it isnt binding and try a different AFM/unplug yours to see if it shuts it off. The fuel pump relay might also be sticking on.

[jlevie]

The fuel pump is controlled by the DME and the fuel pump relay is engaged whent he DME sees timing data from a rotating engine.

[joammo]

Thanks for the replies guys; here's what I did this evening: I checked the fuel pump wiring and it all is good, there has been no molestation of the harness, that I can see or detect with my meter. I pulled out all three relays, and fuze 11 and the pumps still fire up when the key is turned to the ON position. I'm beginning to suspect the DME is fried and it is sending that signal to the pumps. Is that possible? With the history the PO gave me on the car it would not surprise me if the DME were toast.
He told me he bought the car needing an alternator, he bought an alternator at the Zone and put it on but every time he would hook up the cables it would spark and arc like hell; he also mention the harness had been cut and he wasn't sure if it was put back together right. I swapped the engine harness last night, boy was that fun at 100 degrees in the garage! Anyway, now I have a good harness and a good alternator (the one from the Zone ended up being bad out of the box, I replaced it with a good one from a junkyard for 12 bucks). Anyways, I figure I need to get this fuel pump thing fixed before I tackle the no spark at the coil (i've already swapped the CPS around in the trans and their connectors, I have two more off the same car the alternator came off of in case they are bad). So now here I sit with this car that I assured my wife I could fix quickly sitting in the garage in her parking spot dead as a door nail...how do you think my life is going..LOL. Do you think I should swap the DME out? I have an extra here at the house. I just hate putting it in a dead car, the guy who taught me how to work on these things over in Germany told me to never do that. Any further help you guys can give me will be appreciated. I have power on pin 30 only of the main and on 86 of the fuel pump relay with the key off.

[Sagaris]

If the PO had a bad alternator that was overcharging the system then there is certainly the possibility that the ECU could have been damaged by overcharging.

[b*saint]

I can't see the the main relay shorting closed AND the DME shorting closed. If anything the DME tracers would be like filament and short open. Has anyone seen DME's short to ground and close? Also they are probably isolated opto coupled outputs on the DME.

[jlevie]

Thanks for the replies guys; here's what I did this evening: I checked the fuel pump wiring and it all is good, there has been no molestation of the harness, that I can see or detect with my meter. I pulled out all three relays, and fuze 11 and the pumps still fire up when the key is turned to the ON position..

With the fuel pump relay removed the DME is eliminated as a cause of the pump running. And by pulling fuse 11 you have eliminated the engine harness as a possibility. The cause of the pump running will be between fuse 11 and the pumps. It may be a creative "fix" for a bad fuel pump relay, etc., or it could be a fault in the wiring after fuse 11.

[joammo]

OK, I'll double check the wires again then, maybe I missed something last night. Thanks again! I'll let you know how I get on. What about only having power at pin 30 of the main relay socket with the key off? Sounds like someone may have run a wire form the ignition straight to the pumps somehow, I guess I need to focus under the dash then.

[jlevie]

Pin 30 and 86 of the main relay and pin 30 of the fuel pump relay are provided with un-switched power and should be hot all the time.

[joammo]

Got it, thanks! I'll give it all a once over tonight.

[joammo]

Just finished double checked the harness under the dash...oh boy what fun that is! Anyways, I traced the GRN/VIO wire from the fuel pumps all the way back to the fuze box and it has not been messed with. Additionally, I double verified there were no extra power wires going to the pumps of the relays under the hood. Are there any other relays or switches in there that control those things? I looked through the ETM but I don't see anything that would cause this, I guess I will pull the pump out of the tank tomorrow and see if the sock is clogged but other that than I am completely stumped here. When the key is off I have power at pin 30 on both the fuel pump relay block and the main relay block (i do not have power anywhere else on the main relay block) and fuse 11 is dead. When I turn the key on, I have power on fuze 11, and power only on pin 30 of the main and fuel pump relays. Any ideas? jlevie, I will run through your trouble shooting tomorrow on the DME connector and such to see what I come up with but I'm at a total loss. Could it be a jacked up ignition switch?

[joammo]

OK, I went out to start the "no start" trouble shooting and noticed you referenced DME 47 & 48, I only have 35 pins, are those steps for the Motronic 1.3 and up with the 55 pin connector? Also, I disconnected the DME and pulled all the relays out of the fuze box and the pumps did not run unitl I put K5 back in, I'm not following this at all on this car and beginning to regret buying it.

[joammo]

:D It lives! I went through the troubleshooting and after verifying the CPS were good all that was left was the DME. I grabbed my junkyard DME and she fired up. She's surging to beat hell and the temp gauge don't work but at least it runs! I drove her around the block and the slush-o-matic is working well too (that things gotta go!). Thanks for all the help guys and I'm sure you'll hear more from me.

Cheers!
Wendell :up: (for now)