87 325i fuel pump issue

Hey guys, my 325i was sporadically loosing power then bumping back on more and more frequently until finally it died all together.. It was like the fuel pump was turning off and on off and on... Now I've done plugs wires fuel filter and both fuel system relays and the fuel pump does not turn on unless I bridge the relay terminals w a jumper wire in which case the pump fires right up :-/... Any ideas of diagnostics I can perform or ideas of what I can do before gambling w replacing te fuel pump?

Thank you all so much for your time!

-sean

if the fuel pump runs when the relay is jumped, then the pump is fine. youre problem will be something electrical before the relay. starting place is the ignition switch

+1 on above. Now you have to trace back.

Aha, we'll that makes sense. Doesn't sound like a ton of fun or easy to trace but I've got a Haynes manual so hopefully that will direct me a bit. THANKYOU very much ill keep u informed.

Oh and your saying trace back from the relay? Or from the ignition switch. Plz excuse my ignorance :-/

Between the ignition switch and the relay, but first, try swapping in a different relay! I haven't seen that suggested yet. Relays are a common failure point. You already know the wiring from the relay to the pump is good, since it works when jumpered.

I would try another fuel pump relay.
The fuel pump circuit is apparently fine from the main pump up to the fuel pump relay plug.
Jumping 30 and 86 suggests that the 12v from the main relay is ok, so there is suspicion about either the switching inside replacement relay or the switching circuit before the relay which, iirc, is T15 from the ignition switch.

m

Ok cool Thanks for the clarification. Hopefully will be able to get to work on her today.

The fuel pump relay will have +12 volts on the one side of its coil as soon as ignition is turned ON.
The other side of the relay coil however will be waiting for the ECU to connect it to Ground so that the relay will energize....this is what you need to look for!

The ECU will provide this Ground signal to the Fuel Relay only when the engine turns over and the ECU starts to recognize the pulses coming from the Crankshaft Sensor.

So you should read +12 volts on pin 86 of the relay with ignition ON...if you ground pin 87 the relay should energize and the fuel pump should run. If this happens then maybe you need a new Crankshaft Sensor!

Seems like the crankshaft sensor at this point. I have power out of the ecu but still no pump. The pump shows 0.1 volts in the lead that goes to it from this odd white on top of black plugs, which isnt plugged into anything..? Don't really understand that one but I rem seeing it when changing the radio (again not plugged into anything) and the car worked fine back then. Anyway when I jump 86 and 87 I get power to this wire I've been rambling about so seems like crank shaft sensor or fried one circuit in ecu but that's unlikely

Don't test too many things at once. Test one thing, prove it good and move on. If you undo / test several things you may introduce a feed back or fault you did not have to start with. CPS is a coil with about a 300ohm resistance. You can test in situ.

Ok so we noticed the wires to the pump were pinched between the frame and the tank so we were thinking it was a short.. Read the wiring diagram and deteimed the wire goes to the ecu, found the wire and put a jumper on it rigt to the pump.. Sure enough pump turns on and the car starts and runs like a top.. Yay! So then went to the store to get wire etc to bypass the shorted wire and splice it in.. So I cut the wire and spliced the new one on and then onto the connector and onto the pump.. Tried it and now the pump won't turn on :-( so figured only different thing is the wire we cut.. So spliced the cut wire back into the circuit and sure enough the pump turns on w the ignition but now it just keeps running instead of just for a second before I turn it over.. So that's strange.. Now I try to start it and for some reason now there's no spark :-(. All I can think of is that by cutting the wire I messed something up... There's power to the ignition coil and we tested the resistance and its fine.. So something isn't letting the plugs fire... I could cry lol. I'm driving an f150 w a slipping clutch I NEED my car to get to work.. Thought I had it all figured out and now I'm back to the drawing board

In that case wire is wire. If it wouldn't run with the spliced-in piece, it either wasn't really spliced (no connection in the splice) or something else has gone intermittent. That's what seems to be the case with your situation. Most likely the fuel pump relay. I don't see anywhere that you've said you replaced it with a known good one.

Originally Posted by Stoomey006

Ok so we noticed the wires to the pump were pinched between the frame and the tank so we were thinking it was a short.. Read the wiring diagram and deteimed the wire goes to the ecu, found the wire and put a jumper on it rigt to the pump.. Sure enough pump turns on and the car starts and runs like a top.. Yay! So then went to the store to get wire etc to bypass the shorted wire and splice it in.. So I cut the wire and spliced the new one on and then onto the connector and onto the pump.. Tried it and now the pump won't turn on :-( so figured only different thing is the wire we cut.. So spliced the cut wire back into the circuit and sure enough the pump turns on w the ignition but now it just keeps running instead of just for a second before I turn it over.. So that's strange.. Now I try to start it and for some reason now there's no spark :-(. All I can think of is that by cutting the wire I messed something up... There's power to the ignition coil and we tested the resistance and its fine.. So something isn't letting the plugs fire... I could cry lol. I'm driving an f150 w a slipping clutch I NEED my car to get to work.. Thought I had it all figured out and now I'm back to the drawing board

You cannot splice in a new wire and simply cut out the existing wire!
This would work if the wire in question goes only from point A to point B....you cut the wire at points A and B and replace it with another wire...this should work.

But if the wire going from point A to point B also has internal splices going off to maybe point C and point D then cutting this wire at points A and B leaves point C and D in mid air.

What are the colors of the wires you are dealing with? I will have a look at my circuit diagrams. In the meantime return the wiring to its original status...don't cut any wires but try adding in the extra wire from the pump to the ECU as before. This will work if you have a broken wire somewhere but not if you have a wire shorting somewhere.

The wire I cut is green, and I believe the wire to the fuel pump is green w a lavender stripe

Originally Posted by Stoomey006

The wire I cut is green, and I believe the wire to the fuel pump is green w a lavender stripe

yeah the wire going to the fuel pump is a Green/Violet wire...should be no problem replacing that wire as it does not go anywhere else.

I cannot find any Green wire in that vicinity.....what happens when you re-connect it?

My apologies. I have replaced the fuel pump relay and it switches over and the pump turns on.. The problem is when I jumped that wire it was still intact whereas when I spliced it I cut it and only spliced into the side coming out of the ecu, which by doig that and trying to start it... Something happened where I don't have spark anymore

So you tested the cps? And it came back good? I would even try taking it off and checking the tip i believe it magnetically worked but dont hold me to it mine had some road dust and junk so i scraped it off and threw it back on test your cps and get back to us as far as your splice as HH said wire is wire i have to agree check your splices again and if possible butt connect them at the finish line to assure future vibration doesnt knock em loose

Wicked Fast Entertainment

What's the cps? Excuse ignorance plz

Crank position sensor ohm it out if you have access to a meter

Wicked Fast Entertainment