Fuel Pump wiring help

[shakenbake01]

I've dug through a bunch of threads and can't seem to find an answer. Does the output from the LS1 PCM go directly to the wire for the E36 fuel pump relay? Not sure if the polarity matches up or if a relay is needed to reverse it. Thanks

[garretvs]

Start looking at the wiring diagrams. The PCM grounds the coil side of the fuel pump relay; the fuel pump draws too much current to control directly.

[shakenbake01]

Sorry I should have worded it better. I realize that the output of the PCM is just a relay trigger. Just trying to figure out if the E36 fuel pump relay requires a positive or negative trigger?

[BRAAP]

I have also found that GM typically grounds control circuits as well, though 2 of the GM wiring diagrams I looked through show the PCM supplying +12v for the fuel pump relay instead of grounding it.


GM PCM wiring diagram;


Copy and pasted from my build thread;



Hope that helps,
Paul


****AUTO MERGE POSTS***

Shakenbake,
A little digging through the '97 ETM reveals +12v and ground paths.
Hope this helps;

[shakenbake01]

Thanks Paul. That ETM is a handy bit of info. Did you just bypass the ECM relay or run it to an ignition source?

[BRAAP]

Mine is wired as GM wired it, PCM supplying the +12v to the relay control then other relay control wire grounded to chassis. Power fro the controlled side is +12v from battery jump terminal to one side of the controlled pins on relay, other pin to the fuel pump via Pin #13 in X20 connector and fuse #18 as BMW had it, I used a GM relay instead of the BMW relay.

The V8 E36 conversion we are currently working on will be using the BMW fuel pump relay with the controlled side powered via the ECM relay just as BMW did it, only changing the control side allowing the 12v from the GM PCM pin #9 and chassis ground other side, like this;




Hope that helps,
Paul

[shakenbake01]

Perfect. Helps a ton. Thanks. One last question hopefully. What are you using to supply turn on signal to the ECM relay now that the DME is no longer in use?

[BRAAP]

The ignition switch, +12v "on" and "start".

[asinapple8805]

i completely rewired my relays for this. i don't think it's a good idea to just have it kick on with the turn of the key.

my PCM primes the pump when the key initially turns on, but it doesn't keep the fuel pump constant until it sees the crank sensor detecting the crank rotation.

what i did when trying to figure out the wiring was to take a jumper wire with a fuse inline and ground each pin. if the thing didn't kick on when it grounded, then try feeding it 12V+. I don't recommend this for other electronics in the car, but all of the pins in the 3 round connectors should be fine. the worst thing that could happen is you blow the fuse (assuming you use a low enough rated fuse).

[shakenbake01]

I would not wire it that way either. The GM PCM is designed to control the fuel pump relay. BRAPP's wiring diagrams were not suggesting that the pump be on an ignition source only. However it appears to be OK to have the ECM relay kick on with ignition.

[asinapple8805]

Well, if the PCM doesn't kick on with the ignition through a relay, then how else were you planning on turning it on? Just sayin...LOL

[shakenbake01]

THe ECM relay was originally controlled by the BMW DME. It did not control the ignition power to the DME. The GM PCM gets direct ignition power without going through a relay. There is no need to power the GM PCM through a relay.

[asinapple8805]

I ran my fuel pump, my coils, my injector power, and my PCM power all through different relays. I also powered all the relays off of one relay to provide signal. It's a little overkill, but i had a good reason for it. My idea was that I could use it as an anti theft device and also for trouble shooting purposes. To each his own.

[shakenbake01]

The anti-theft idea is nice. That is something to think about.

[TipsyMcStagger]

I have old fuel in the tank I want to pump out. Normally, jumping BMW Fuel Pump relay (X6301) Pins 87 & 30 would activate the fuel pump. But in my current state of dismantled chaos, there is no fuel pump relay wired-in.

Am I understanding the below diagram correctly? Will grounding X20-13 provide power to the fuel pump?

Thanks!

Tipsy

Mine is wired as GM wired it, PCM supplying the +12v to the relay control then other relay control wire grounded to chassis. Power fro the controlled side is +12v from battery jump terminal to one side of the controlled pins on relay, other pin to the fuel pump via Pin #13 in X20 connector and fuse #18 as BMW had it, I used a GM relay instead of the BMW relay.

The V8 E36 conversion we are currently working on will be using the BMW fuel pump relay with the controlled side powered via the ECM relay just as BMW did it, only changing the control side allowing the 12v from the GM PCM pin #9 and chassis ground other side, like this;


Hope that helps,

Paul

[Schitzo]

I have old fuel in the tank I want to pump out. Normally, jumping BMW Fuel Pump relay (X6301) Pins 87 & 30 would activate the fuel pump. But in my current state of dismantled chaos, there is no fuel pump relay wired-in.

Am I understanding the below diagram correctly? Will grounding X20-13 provide power to the fuel pump?

Thanks!

Tipsy

No; you need 12v at X20 pin 13 to power the pump.
I too have to drain old fuel from my tank but I'm doing it manually with a suction pump. It'll suck.

[TipsyMcStagger]

No; you need 12v at X20 pin 13 to power the pump.
I too have to drain old fuel from my tank but I'm doing it manually with a suction pump. It'll suck.

Thanks. This project has dragged on for so long I've data dumped a ton of information.

So just jumper 12v directly to X20-13 (from X0) and the fuel pump should activate?

Tipsy

[Schitzo]

Correct.

[TipsyMcStagger]

Correct.

Thanks!