Fuel pump relay loses power when acc turn on...?

[MIKe30]

Just got my m50 swap running today. At first it wouldn't start, but I realized it was due to my fuel pump not having any power. Powered it up with a 12v battery and heard the gorgeous sound of open exhaust manifolds after a successful swap :)

After poking around with a meter, turns out my fuel pump relay has power fed to it when the car is off. Of course, the relay is not triggerred and there is no feed out to the pump.

Turn the key to on as if you were about to crank the car, you can hear the ICV click on and start it's usual buzzing, simultaneously the 12v feed for the fuel pump relay drops to 0v and the two relays next to it are completely energized at 12v.

Any ideas what may be causing this? All my fuses are good, checked them not only visually but with a meter, too. I'll double check to make sure my fuel pump relay fuse is even where it should be, maybe it was moved by accident sometime. Other than that I'm not sure what could be the cause. Should I just tap off the power from the other two relays that seem to get switched to 12v on everytime the key is on?


Thanks in advance amigos.

btw, engine is an obd1 vanos m50. I have power cables from the big starter post to + battery lead/post in the bay, along with 3 other cables that are +'s coming off the harness.

[mbonder]

I don't have an answer for you, but its good to hear that the engine fired up for you

[MR E30 325is]

I also have no advice, but my almost completed S52 swap doesnt have any fuel either.

Can you tell me what you powered the pump via the 12v battery?? I want to make sure the fuel problem is the only problem that i have with the car not starting.

[MIKe30]

I don't have an answer for you, but its good to hear that the engine fired up for you

Thanks Matt. It sounded pretty solid too, even without an o2 sensor attached :)

I also have no advice, but my almost completed S52 swap doesnt have any fuel either.

Can you tell me what you powered the pump via the 12v battery?? I want to make sure the fuel problem is the only problem that i have with the car not starting.

Your question isn't quite clear, but if you're asking about what I used to power the pump when my car wouldn't do it by itself - I used a 12v battery out of a commercial fire alarm panel. (I always carry a few around for work, funny enough - it's gotten me out of a jam or two with my car in my day).



Hoping somebody has an idea.

[SamE30e]

Sounds like you wired something wrong. The fuel pump relay should have power to it when the car is off, the relay coil just isn't triggered to complete the circuit to power the pump. My guess is it's your relay coil wire.

[MIKe30]

Sounds like you wired something wrong. The fuel pump relay should have power to it when the car is off, the relay coil just isn't triggered to complete the circuit to power the pump. My guess is it's your relay coil wire.

that's exactly what I said in my OP.

I'm thinking my relay is bad, and when it's supposed to trigger it shorts instead - dropping my power to 0v. I will see tomorrow if my power feed to the relay still drops to 0v when the relay is pulled out and I turn my key to the on position. That should answer some questions.