HELP! Quick fuel pump wiring question

[gagliano7]

It depends how you wired it but if you wired like i did connecting the fuel pump power from the new pcm to the power going to the fuel pump where the relay is under the hood without the oil pressure hooked up it won't work.

[exboatracer]

My fp relay wire is connected to the grey wire that comes from the c-100 firewall connector and it powers right up. Also my oil pressure sender is not installed yet and the engine runs. I also thought the tan wire from the oil sender needed to be hooked up to the fp wire so thats a puzzle to me too. Like gagliano7 said, maybe theres a different way to connect them. This is on a 1990 truck,5.3 4l60e swap with a NP harness. Try checking your grounds.

[lost06]

Ok. Heres what I have so far....

Terminal 86 on the relay should be a constant ground. But with the volt meter, it shows to be putting out around 12v. I am attaching a generic diagram I made. I was thinking that maybe i should ground the relay directly???

[exboatracer]

I forgot to tell you an important part of my initial start-up. My first attempt to power up the fuel system (to check for leaks) failed.I turned the key and nada. Went looking and found a blk/wht wire coming from c-100 and according to my wiring diagram it was a ground. Hooked it to the firewall and the f/p powered right up. I'm not good with wiring but I hope this helps or someone else can chime in.

[lost06]

Thanks. Ill look when I get home. However, I cut the wire and grounded the end going to the relay and it primed but quit cranking. So I reconnected the wires and it would crank again but no fuel pump.

[capricefrk013]

Untitled5.jpgGoing through the oil sender is probably a safety feature to shut the fuel pump off in case of a roll over. Pin 87A on the relay "should" be connected to the oil sender. This could be incorrect and maybe some will chime in to confirm that.

I forgot to tell you an important part of my initial start-up. My first attempt to power up the fuel system (to check for leaks) failed.I turned the key and nada. Went looking and found a blk/wht wire coming from c-100 and according to my wiring diagram it was a ground. Hooked it to the firewall and the f/p powered right up. I'm not good with wiring but I hope this helps or someone else can chime in.

That Black white is a ground feed fed by the ECU to trigger the relay to turn the pump on.

Thanks. Ill look when I get home. However, I cut the wire and grounded the end going to the relay and it primed but quit cranking. So I reconnected the wires and it would crank again but no fuel pump.

I Need to know what wire does what to better help you figure this out but maybe this pic can help you figure out what goes where.

[lost06]

Please see my post here. http://www.ls1truck.com/forums/lsx-t...ease-help.html

it might be a little more descriptive.

Thanks for the help and advice

[exboatracer]

Thanks caprice for that oil sender rollover info. When I removed the old 350 I marked that tan wire that came from the oil sender since it was tied into the f/p wire. (I had no idea why oil sender and f/p relay could be related). Now I'll tie it back in.

[exboatracer]

Hey lost06, can't wait to hear that you your problem is solved. Let us know, it's usually something simple. Don't lose hope,it will work out.

[lost06]

yeah, it was really simple. I grounded that set of grounds to the coil bracket on the valve cover. Apparently, this is a bad idea. I moved the ground to the alternator bracket and my gauge started working and the pump kicks on.

Now, my truck would crank over BEFORE i would ground the fuel pump relay. Now it won't crank. I had an issue where the PRNDL switch wasn't allowing it to crank. I bought a new one and it fixed that problem. Now since I fixed the fuel pump.... it wont crank again...


GRRRRRRRRRRR!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!