S50 died and won't start

[Ian Bowers]

I've got an 87 325E with an s50 swap. I was driving on the hwy and the car started to sputter, then died. It cranks, but just has no fuel.

I've ohm'd the Crank and Cam pos sensors, they both check out (550/2000)
Checked for power before/after fusable link (good)
Checked for power at fuel pump relay (all pins have power)
Checked for power at fuel pump fuse (good)
Checked for power at fuel pump (good)

If I jump the fuel pump relay, the pump does not prime. I assumed it was the fuel pump itself, so I took it out and replaced it with another known working pump, and it still won't prime.

Anyone have any ideas?
Thanks in advance!

[Ian Bowers]

Beuller... Beuller?

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[M3PO]

I don't see how you can have power everywhere and a good pump but it won't prime if you jump the relay.

[Ian Bowers]

Right? In other news, I was holding a test light to the green/violet fuel pump relay wire while cranking, and it triggered the relay or pump? I don't know why, but it runs again.

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[FredK]

If you jump the fuel pump from Terminal 30 to 87 and it does not power up, there's clearly something wrong with the wiring. Can you confirm that you are indeed jumping these two terminals? If this is the case, can you describe what you've done downstream with pump wiring? I believe the pump is grounded at G300. It may be worthwhile to pull your seat up and clean and check ground nut tightness.

Your other symptom of having the car fire up after using a test light on T87 would indicate to me that there is possibly something wrong on the relay control side of things. If by adding the inrush current of lighting a test light bulb causes current to flow from 30 to 87, it would seem to me that there's an issue of the coil fully engaging. By adding the large instantaneous load of the test light, maybe it's enough to coax the relay to the fully closed position.

[Ian Bowers]

I'm definitely jumping 30 to 87. Currently, pump wiring is stock (in tank lift and external pump). I also have had it wired with a single in-tank 255 from a 318iS, no change. Checked the ground, it's clean and tight.

I believe you are correct that the issue is on the relay control side. I am curious if maybe the harness has an issue that I haven't seen, or if the ecu is being the issue. It only happens on hot days.

If you jump the fuel pump from Terminal 30 to 87 and it does not power up, there's clearly something wrong with the wiring. Can you confirm that you are indeed jumping these two terminals? If this is the case, can you describe what you've done downstream with pump wiring? I believe the pump is grounded at G300. It may be worthwhile to pull your seat up and clean and check ground nut tightness.

Your other symptom of having the car fire up after using a test light on T87 would indicate to me that there is possibly something wrong on the relay control side of things. If by adding the inrush current of lighting a test light bulb causes current to flow from 30 to 87, it would seem to me that there's an issue of the coil fully engaging. By adding the large instantaneous load of the test light, maybe it's enough to coax the relay to the fully closed position.

Sent from my Nexus 6 using Tapatalk