Fuel pump relay (problem fixed)

#1

What should the voltage be on the upper middle connection, 12:00 position if your standing by the fender looking at the engine, on the fuel pump relay?

Mine reads 12v with the ignition OFF and around ~193mV with the ignition on.

The engine will not run and after a lot of trouble shooting I’ve traced it down to the fuel pumps not working when they should. They will work if the 6:00 and 9:00 terminals are jumpered. I’ve switched relays with the O2 heater relay amd have also tested the relay to see if it is working. I’ve swapped in two other DME’s eo see if that solved the problem, of course they could be bad.

I’m beyond my knowledge and skill set, any help would be appreciated!

#2

Just to clarify when you jumper the relay, just the fuel pumps run or the whole car runs?

#3

Fuel pumps run.

The car, fired when I squirted gas in the intake. But it won’t start with the fuel pumps jumpered.

#4

So if the relay is in, the pumps don’t work. If the relay is jumpered they do work but the car still doesn’t run? You said the car fires - does it actually run? I’d be curious about whether you’re getting spark to the cylinders, and also testing the main relay which signals the FP relay among other things.

#5

I’d replace all of the relays just to be safe. If they are original their probably getting worn anyway. I don’t remember them being that expensive and I got them from the dealer.

#6

If the relay is jumpered the pumps work, but the car won’t run.
The car ran for a few seconds when I squirted gas in the intake.

The car has ignition to all cylinders, although the park looks weak to my eye. The coil is within the spec listed in my Bentley.

I called a friend with an e30. His 12:00 connector has 12v with the ignition on, 0v with it off. This is what I would expect to happen. Do I have a short on this circuit - does it get its power from the DME?

I want to see what this connector does whenthe starter is turning over the engine, but my arms aren’t long enough. I understand you can power the starter through the diagnostic plug - which connectors?

TIA

#7

Did you download the electrical troubleshooting manual? It’s pretty helpful when you trying to verify that you’re getting voltage to everything. I think there is a link to it from this site from the “Links” section on the left of the page.

#8

drumbeater wrote:

Yes, I have. But I’ve not started using it yet. I’m a moron with electrical issues.

What causes the flapper valve by the AFM to open (above the air filter)? Is it electric or vacuum?

#9

Well our first instincts at the track turned out to be right. When the car died at the track my son ran into town and got a new main relay from a local auto parts store, but the car still wouldn’t run. After much frustration at the track and after we got home I figured out today that the main relay was the problem after all. It was not sending out power to the FP relay when the ignition was on, it sent it when power with the ignition off. The old relay acted the right way but it sent only 2V to the FP relay. I went to the BMW dealer, got a new $15 main relay, put it in and the car fired right up. I hope that’s the end of my gremlins.
Don’t buy aftermarket Duralast relays.

#10

Glad to hear it Mark. Another thing about this is that IIRC the FP relay wants to see at least 8v from the main relay. So in some cases the main may be sending voltage but not enough for the ECU to signal the FP relay. I just add that for future researchers as I learned it last year. Replaced all my relays as part of troubleshooting, but mine turned out to be a bad connection inside the kill switch impeding the voltage. Glad to hear yours is running again.