Weird EFI fuel pump problem

[crawlin68]

I had the Bronco out of the garage yesterday fixing some last minute items and taking the top and doors off in preparation for the Rubicon Run. When I went to start it to pull it back in the garage, the fuel pumps quit running. This has happened before and it was the relay that runs the pumps. So I thought this is what must have happened again. I installed a new relay and the pumps still don't come on. Because it was getting dark, I just hot wired the pumps from the Self Test plug to make the pumps run. It starts right up and I pull it into the garage (now this is the weird part) when I turned the ignition key off, the engine kept running! It wouldn't shut off. WTF?? The only way I got the engine to shut off was to pull my hot wire out of the Self Test plug, and then it died immediately. Now I have no idea what's going on.

[CityHick]

Re: Weird EFI fuel pump problem

This is going to take two people to accomplish since you can't be in two places at once.

My theory is your computer isn't sending the trigger voltage to the relay that runs your fuel pump(s). The fact that the hotwire trick worked makes me suspect computer weirdness even more.

Have someone get in your Bronco while you watch a volt meter that's connected to the input/triggering side of the fuel pump relay (the wire that comes from the computer to kick the relay over). When the ignition key moves to the run position the computer is supposed to trigger your fuel pump relay for 2 seconds to prime the system right? See if you are getting voltage at the relay and if not, something's wonky with the computer. Also do the same thing while someone cranks the engine over.

Your harness has inputs from both start and run on the ignition switch - if the above testing doesn't tell any stories perhaps check the connections where the EFI harness joins your vehicle harness.

This is confusing... and I want to see you up at the 'con.

[Filgas]

Re: Weird EFI fuel pump problem

If the relay checks out, it could be the inertia switch. It's job is to cut the power to the fuel pumps.

[pippinmader]

Re: Weird EFI fuel pump problem

It sounds like a computer to me also. It seems unlikely, but could you have supply power to the fuel pump test port instead of ground? Doing that would back-feed the whole EFI system and make it keep running, unlikely but possible. CityHick has a good idea about testing the system, but the signal the computer sends is a ground, so that voltage on the computer side of the coils of the relay (pin 22) should go from 12 to 0 for 2 seconds when you turn the key on.

I am having the opposite problem right at the moment, my fuel pump runs continuously, as soon as the key is turned on, maybe I should have unplugged the computer before welding on the body

[Spaceburger]

Re: Weird EFI fuel pump problem

Check your EEC Relay.

[tim]

Re: Weird EFI fuel pump problem

Check your eec ground!

I just went through this on a mustang and finally figured out that the main eec ground wasn't connected and wasn't trigering the pump to run (actually the pumps would run in the start position but as soon as you released the key, they would die).

Hopefully your issue is a simple fix.

[crawlin68]

Re: Weird EFI fuel pump problem

All good ideas! I'll be checking all of these on my next day off. Thanks.

[tim]

Re: Weird EFI fuel pump problem

Just to clarify, the problem with the eec ground I was having was the one that goes to the battery -, not the local eec case ground.

eec pinouts 40/60.

[Spaceburger]

Re: Weird EFI fuel pump problem

The reason I say check your EEC relay is because if it was dead and you hot wired the system, you back fed the computer 12v and that's why it started and ran. I think that relay is interchangeable with the fuel pump relay...same pinouts...i think.
The relay tabs prevent the mechanic from swapping them by mistake...but you can cut the tabs off and use those two relays interchangeably. Good to know if you carry trail spares.

[crawlin68]

Re: Weird EFI fuel pump problem

Can anyone that is running an RJM EFI harness tell me what the 4 relays under the hood are for? I have my instruction manual from RJM, but the schematic it only has them labeled A, B C and D. But it doesn't say what each relay runs. Does anyone know?

[California Monkey]

Re: Weird EFI fuel pump problem

a= o2 and mass air
b= fuel pump
c= coil & tfi module
d= ecm, injectors, iac

[crawlin68]

Re: Weird EFI fuel pump problem

a= o2 and mass air
b= fuel pump
c= coil & tfi module
d= ecm, injectors, iac

Awesome. Thank you!

[crawlin68]

Re: Weird EFI fuel pump problem

Well, I am stumped. My inertia switch was ok. I switched out the ECM and that didn't change anything. All four of the engine management relays are in good working order. I tried to run the codes, but when I turn the key to the run position, my check engine light just stays on solid. No flashing or anything like it normally would do.

[crawlin68]

Re: Weird EFI fuel pump problem

And when I ground the fuel pump connector in the Seft Test plug, nothing happens.

[tim]

Re: Weird EFI fuel pump problem

Check continuity between 40/60 pins on the EEC connector (harness side) and the negative post on the battery (with battery cables connected). If it shows an open circuit, the computer wont send a signal to start the fuel pump.