No start 89 302

the computer shouldnt tell it not to turn on, i would hook up a 12v source to it and see if it comes on like that, if it does its probably the relay. if not its definetly the pump.

Probe the FP relay socket and post what values you have. You should have one constant power wire, one ground (with the key on) and two more that show 12 volts when the key is on.

Good luck.

no, thats the fuel pump connector, i am pretty sure the fuel pump relay is the one under the passenger seat.

wildstang87 said:

no, thats the fuel pump connector, i am pretty sure the fuel pump relay is the one under the passenger seat.

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Correct, except for it being under the driver seat. to test the terminals, it often has to be done while the pump is priming. So set your meter up on the terminal to be tested and turn the key on. This gives you a couple second window to read results (before the pump stops priming).

A quick and dirty test is to ground the FP terminal on the ST connector and see if that makes it come to life (basically that just tests to see if the puter is sending ground to the control side of the FP relay).

Good luck.

i think the relay is under the drivers seat.

jerryD said:

i think the relay is under the drivers seat.

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Ohhh, Good catch (again) Jerry. I just corrected someone about the passenger seat thing the other day, but missed the passenger part today. Again, It is under the driver seat .

I will edit my above post so illustrate this, so as to remove confusion.

Check the wiring lead that runs from the battery all the way to the relay under the drivers seat, I had mine burn the F up and melt into the carpet and everything for some damn reason until the fuse link thing near the battery burned up and disintegrated. So I replaced the relay and ran some 8 guage wire with a 10 amp inline fuse directly from the battery to the relay, works super duper now

my$100project said:

Is the FP relay easy to access under the seat? I am not able to pull a schemuatic, but am I correct in assumming the power flow is thru the FP relay, then to the inertia switch? IF this is so, couldn't I kill three birds with one stone?
basically, Rather than finding the FP relay to be good, then going to the inertia switch and finding it bad, Just testing power to and out of the inertia switch should tell me the problem. Basically, if no power to inertia switch then it's the FP relay, (then I would check the relay to check for constant 12v and output 12v.) If there is power to the inertia switch and no output then its the switch. If output then it would have to be the fuel pump. Please correct me if I am wrong, but wouldn't this method be more time efficient?

Click to expand...

Yeah, the relay is under the front part of the seat (run the seat all the way to the back of its track). Ok, quick run down on the FP relay. it has a power and control side. The control side has key-on 12 volts. This wire goes through the inertia switch on the way to the relay, not afterwards. It also gets a ground pulse from the computer itself. When both of those are present, the relay can energize (and that is why when the inertia switch trips, 12 volts does not make it to the relay's coil, and the coil will not energize).

The power side has a power wire from the solenoid (what VP talks about in the previous post). there is a fusible link just off the starter solenoid on this wire. then the relay has a wire leading out of it to the pump itself. In order for the last wire to get 12 volts, the other 3 wires have to supply what they do. Otherwise, no power to the pump.

You are right about the inertia switch. If there is 12 volts in, but marginal volts out (some folks see 3-4 volts out, when the switch is on the outs), then the inertia switch is a problem. One can (for testing only) jump the inertia switch to confirm it is the issue.

Good luck bud.

One wire (Probably tan/lt grn, if you have one of those - it looks like you do) should show ground while the pump is on, not 12 volts).

So it appears to me (anyone, please correct me if you see that I missed something) that you should have power to the FP. Pink/Blk is what is the output to the pump (You could run a jumper to this wire for testing purposes). So either there is a bad connection at the pump or there is a restriction of some sort. Once you get pressure at the Schrader valve, if still no go, check that the injectors are firing.

Again, if you have 12 volts while priming AND cranking at the pink/blk wire, that should be money (and suggests that the FP relay is working).

Thoughts on any of this?

Good luck bud.

Oh yeah, here is a diagram from S+2B's site (diagram authored by Tom Moss). THough it is for an 88, the wiring colors you tossed out seem to be similar/the same. It might help you see what we are talking about.

Good luck.

My 2 cents worth - much of this has already been discussed, but some thoughtful review always helps...

Clue – listen for the fuel pump to prime when you first turn the ignition switch on. It should run for 5-20 seconds and shut off. To trick the fuel pump into running, find the ECC test connector and jump the connector in the lower RH corner to ground. See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html for a description of the test connector. If the relay & inertia switch are OK, you will have power to the pump. Check fuel pressure – remove the cap from the schrader valve behind the alternator and depress the core. Fuel should squirt out, catch it in a rag. A tire pressure gauge can also be used if you have one - look for 37-40 PSI. Beware of fire hazard when you do this.

No fuel pressure, possible failed items in order of their probability:
A.) Tripped inertia switch – press reset button on the inertia switch. The hatch cars hide it under the plastic trim covering the driver's side taillight. Use the voltmeter or test light to make sure you have power to both sides of the switch
B.) Fuel pump power relay – located under the driver’s seat in most stangs built before 92. On 92 and later model cars it is located below the Mass Air Flow meter.
C.) Clogged fuel filter
D.) Failed fuel pump
E.) Blown fuse link in wiring harness. Use a voltmeter to measure the voltage drop across them. There should be less than .75 volt drop across a fuse link.
F.) Fuel pressure regulator failed. Remove vacuum line from regulator and inspect for fuel escaping while pump is running.

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 power for any actuator or relay, 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/tech/engine/images/IgnitionSwitchWiring.gif

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

Now that you have the theory of how it works, it’s time to go digging.

Look for 12 volts at the Orange/Lt. Blue wire (power source for fuel pump relay). No voltage or low voltage, bad fuse link, bad wiring or connections. There is a mystery connector (one I haven’t found) under the dash somewhere, between the fuel pump relay and the fuse link.

Turn on the key and jumper the fuel pump test connector to ground as previously described. Look for 12 volts at the Light Pink/Black wire (relay controlled power for the fuel pump). No voltage there means that the relay has failed or there is a broken wire in the relay control circuit.
Check the Red/black wire, it should have 12 volts. No 12 volts there, either the inertia switch is open or has no power to it. Check both sides of the inertia switch: there should be power on the Red wire and Red/Black wire. Power on the Red wire and not on the Red/Black wire means the inertia switch is open.

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 and only if you have followed the test procedure to this point and still haven’t found the problem, the computer is suspect.

JR - We were waiting. Much easier to follow your articulate, complete post than my recursive, random thoughts.