Big Fuel Problem!!!help!!!

[gooch06]

Ihave a 1990 LX 5.0 and my problem is getting my fuel pump to run. I bought a brand new fuel pump and relay.

My problem lies in the ground wire. When I ground the Tan and Green wire the pump runs.
The wire is good from the computer to the relay.

Can I just ground the wire to the frame or does it have to be grounded to the computer.
The ground on Computer is fine.
Can I take the computer out and get it tested or reset?
Does something tell the computer to supply the ground?

 

[HISSIN50]

I am not in the same league (about 10 below him) as Tom, but *I think* a bad ground strap in the puter can cause the ground pulse to the relay to not be sent.

some guys have wired the ground to a relay so that the FP relay gets ground when the ignition is on. not the best way to do it, but.......

If Tom (Or Joe or one of the other wisemen) see(s) this, they will have ideas for ya.

good luck.

 

[rd]

I think Ford powers the fuel pump relay full time with the ignition on, and uses the computer to ground it to actually turn the pump on. Most EEC stuff is set up this way. The fuel pump control circuit includes the computer control wiring, and the crash sensor switch, so make sure all of that is working.

With ignition on, the fp relay control wire should have power. Then check the actual power wiring to the relay that powers the pump to make sure it has power and ground.

 

[gooch06]

I can get power as long as i ground the wire. The wire is good all the way to the computer. The computer ground is fine.

 

[gooch06]

Is it okay to ground the wire to the chasis since the EEC is grounded to the chasis. Would't they share a common ground then?

 

[HISSIN50]

I can get power as long as i ground the wire. The wire is good all the way to the computer. The computer ground is fine.

You lost me. Do you have a ground pulse reaching the FP relay from the computer (when probed at the FP relay)? I assumed you did not. is this right?

what it sounds like you are doing is not unlike grounding the same wire at the self-test connector, which people do for diagnostics.

When you said the computer ground is fine and that the ground wire is fine, I had assumed you meant the ground for the EEC (at the battery neg ground bolt) was alright, and the actual wire was alright (not open) from the puter to the FP relay. Maybe we are missing something here (for others, I have replied on another thread or two of Gooch's on SN and one on the Corral - so some stuff might seem like intangibles as new threads keep popping up rather than continuing the original thread).

Anyhow, good luck.

 

[gooch06]

Only can get the pump to run when I ground the beige wire w/ light green stripe. If I test the EEc where that wire goes in nothing until I ground that wire. It has to be the ground. Does the EEc have to be cleared or reset to have the ground work? When I check the eec and that it is grounded to the chasis it is ok.

 

[gooch06]

Do you have a ground pulse reaching the FP relay from the computer (when probed at the FP relay)?

Only when I ground the beige w/ light green stripe.

 

[HISSIN50]

gotcha. This is what I had thought originally. running a ground wire through a switch to the FP relay, through a relay to the relay or fixing the issue with the puter (where I would talk to Tom) sounds like the solution (or swapping another puter).

I just wanted to make sure - I get lost when multiple threads pop up (I dont recall exact details from previous threads). (happens when you get old).

good luck.

 

[gooch06]

Can I just ground the beige w/lightgreen stripe wire to the chasis?

 

[Stang8URMPRT]

Sure, if you want the pump to run at full capasity at all times, go of it

 

[jrichker]

The electrical circuit for the fuel pump has two paths, a control path and a power path.

The control path consists of the inertia switch, the computer, and the fuel pump relay coil. It turns the fuel pump relay on or off under computer control. The switched power (red wire) from the ECC relay goes to the inertia switch (red/black wire) then from the inertia switch to the relay coil and then from the relay coil to the computer (tan/ Lt green wire). The computer provides the ground path to complete the circuit. This ground causes the relay coil to energize and close the contacts for the power path. Keep in mind that you can have voltage to all the right places, but the computer must provide a ground. If there is no ground, the relay will not close the power contacts.

The power path picks up from a fuse link near the starter relay. Fuse links are like fuses, except they are pieces of wire and are made right into the wiring harness. The feed wire from the fuse link (orange/ light blue wire) goes to the fuel pump relay contacts. When the contacts close because the relay energizes, the power flows through the contacts to the fuel pump (light pink/black wire). The fuel pump has a black wire that supplies the ground to complete the circuit.

Remember that the computer does not source any power to actuators, relays or injectors, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

http://www.veryuseful.com/mustang/t...witchWiring.gif

http://www.veryuseful.com/mustang/t...inks-ign-ac.gif

http://www.veryuseful.com/mustang/t...91eecPinout.gif

The Tan/Lt Green wire provides a ground path for the relay power. With the test connector jumpered to ground, there should be less than .75 volts. Use a test lamp with one side connected to battery power and the other side to the Tan/Lt Green wire. The test light should glow brightly. No glow and you have a broken wire or bad connection between the test connector and the relay. To test the wiring from the computer, remove the passenger side kick panel and disconnect the computer connector. It has a 10 MM bolt that holds it in place. With the test lamp connected to power, jumper pin 22 to ground and the test lamp should glow. No glow and the wiring between the computer and the fuel pump relay is bad.

If all of the checks have worked OK to this point, then the computer is bad. The computers are very reliable and not prone to failure unless there has been significant electrical trauma to the car. Things like lightning strikes and putting the battery in backwards or connecting jumper cables backwards are about the only thing that kills the computer.