I have hesitated to post since I think folks should read first but I have been chasing this trouble and reading old post for over a month, off and on, and the problem still exist. I have a 88' F150 5.0 w/ C6 tranny 4X4. I can not get the fuel pumps to run. When you turn the key on the fuel pump relay does not click and the pumps stay off resulting in zero fuel pressure. I pulled the relay out and there is 12 volts available from the key and if I jump across the plug and send power to the pumps thru the inertia switch, they both start up and run. I realize that the relay is only energized briefly when you turn the key on so I might not be able to see it with a meter but it should be making the coil in the relay pull in to hear it click, shouldn't it? I checked continuity from the other two posistions of the relay plug, which actual run the relay coil. One leads to pin 22 of the ECU (tan w/light green trace), and the other (red), ties into the red wire that run from various engine devices including the injectors. Both wires tested out fine. This led me to think that perhaps the computer was faulty. I put a rebuilt one in it yesterday with the same reults. Nothing!!! Any help you folks can offer will be appreciated.

 

It sounds like the relay is at fault. You said you disconnected the relay and found a 12v supply, and when you jumped/bypassed the relay you heard the pumps engage. I got a fuel pump relay from autozone for $11, just pick one up and try it out.

 

Yes, I thought so too and tried that, sorry I neglected to mention it! The 12v that I measured is for the pumps, not the voltage that operates the relay. In the relay plug, there are two larger wires, which run the pumps and two smaller wires that run the relay.

Thanks for the response!

 

Good advice from mike. You should also spray an electrical contact cleaner into the plug connector.
However the fuel pump relay energizes when the computer grounds it and you should hear it click. I would check all the grounds. Check the ground to the computer, ground from battery to body, body to frame and grounds to engine.
Hopefully some of the experts will give an opinion soon.

 

Does the the computer obtain ground thru it's retaining clip?

 

Sounds like the small black wire with a green stripe does not have a good ground at the NEG (-) post of the battery.
The wire may leave the post as a black wire and in a about 6 inches have a one wire in-line connector and then it turns into the black wire with a green stripe.
This wire is the ground wire for the computer and relays and must have a good ground at the NEG post of the battery.

Yes and no but not for the relays and injectors.

Computer plug J1 pins 40 and 60 go to the black wire with a green stripe in the bottom left of the diagram below:

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Fuel Pump Relay Circuit:

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Thanks for the info! The computer ground is where I will check next!

Nice schematic Subford! It truly is worth a thousand words!

 

Well, I finally got the time to check out the ground for the computer. I unhooked the plug from the computer and verified continuity from the plug at pins 20,40 &60, to the neg post of the battery, looked good. While I was at it, I cleaned and snugged up the ground straps. One from the engine to the firewall and then to the hood, one that comes out of the computer plug harness about three ins. from the plug and attchs. near the hood hinge, one behind the drivers headlight, one from the intake to the wiper motor. Still no respone from the fuel pump relay.
My next thought is that the red wire coming into the fuel pump relay has issues. As previouls mentioned, I did a continuity check between pin 22 and the red wire at the plug but maybe it is shorted out somewhere and that is preventing the 12 volts from getting there. That red wire runs to many different locations on the engine so I guess I will have to trace it out and see what' up.
Any other suggestions? Dynamite maybe?!?

 

Does the fuel pump relay click and the pumps come on when you ground pin #6 of the EEC Self-Test connector (plug) with the key on?






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No, it does not!

 

Does the red wire have power on them anywhere with a test light and the key on?

 

Just ran back out and checked. No, there is only a little over three volts. I checked at the fuel pump relay plug, the EGR vacuum regulator solenoid (EVR) and the thermactor air bypass solenoid (TAB). That looks fishy to me! I am using a Digital Multi Meter.

 

I will take that as zero volts, it is a lot easier to troubleshoot this circuit with a test light.
Is your EEC Power relay (the brown one) clicking when you turn on the key?

 

Yes, that's the one located in the same plastic housing as the fuel pump relay right?

 

Yes it is.
If it clicks that means either that relay is bad, the wiring under its relay socket is bad or one of the fuse links is bad.
You can check a fuse link by trying to stretch it. If it stretches it is bad.
I am betting that the wiring under that relay is bad where it attaches to the socket.