Cranks, no fuel pump, relay is good!

O/LB should be the link for the FP. So if jumpering it made something happen that didnt before, repairing the link would be in order. It's 18 AWG IIRC, but double check that.

Does it make any noise when you try to start it? If not, I would check the starter interlock circuit (clutch safety switch, jumped NSS that you messed with, etc).

See Jrichker's no start checklists for more (and outstanding) info.

Good luck (and interesting username).

I liked the translation of your last name.

I hear what you are saying. I am wondering if your ground to the FP is shorted (in its run or at the self test connector). I would check it at the test connector to make sure it wasnt bumped (jumping it, as you know, can make the pump stay on). But with a burned link (or no jumper), the ground alone cant activate the pump since the pump has no feed juice.

It sounds like you are all over the white/pink wire (that is the starter interlock circuit if I recall the colors from memory correctly). As long as you have 12 volts at the S-terminal on top of the starter solenoid while cranking, that circuit would appear to be intact.

For finer tuning, I like to probe the relay socket for the FP relay (under the driver seat on your '90). It's like a 4 way stop and seeing the values there gives an idea of which way to go). You already know one direction, but in case you fix the link and/or computer controlled ground and still have an issue with the pump..........

Thinking aloud with you. Good luck.

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://forums.stangnet.com/attachment.php?attachmentid=40907&d=1134531771 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.

DNeinstadt said:

Key IN and turned over (non-crank)
T/G 0v
R/B 0v
G/LG 11.55v
P/BL .02v





Dan

Click to expand...

Dan, was this while the pump should have been priming (right after the key is turned on)? If so, you should see ground on the T/lt grn wire. Also, you should have key on 12 volts on the red/blk wire. I would recheck that at the inertia switch (make sure you dont find 12 volts going into the inertia switch but not coming out - that would indicated an inertia switch issue).

There is a ground strap integral to the puter for the FP ground. Real smart, savvy folks like Jrichker or Tom can fix that - I cant. Since the test port grounding method doesnt help, that suggests the puter ground strap is not necessarily an issue. The very first think I would do is make sure that I get key-on 12 volts to the control side of the FP relay.

As you know, when you jump power to the pink wire, you are sending power directly to the pump, bypassing the relay altogether.

Good luck.

Wow Dan, you gotta let someone else post in between your posts. J/K man - I know this stuff is frustrating.

Jrichker, TMoss, et al blow me out of the water, but I will toss out a couple cents (it cant hurt).

Look at Jrichker's links again - I ask anyone to find finer diagrams anywhere. The colors might not match exactly (they should be about spot on though), but the pathways should all be the same (the diagrams are based on an 88 GT IIRC).

I would check other items that the EEC relay powers (TAB/TAD, injectors, ISC, etc etc) to see if they have power. If they do, the EEC relay works and the issue is specific to the EEC relay wiring for the FP control side. If those other items are dead, check the power supply for the EEC relay (see the diagrams for the schematic). If you need to access the EEC relay, it is above the computer in the pass kick panel. JR has tips on accessing it through a speaker opening IIRC.

If the FP relay only gets ground when you ground it yourself, the ground strap in the puter might be broken. Or in the run of wire between where the line branches off to the test connector and the computer, it might be open (testing the value at the computer would tell you this). As a temporary means, though hideous, you could run a switched ground (via a manual switch) or run a switched ground via a relay (use a key-on 12 volt input and use a ground on the common terminal in the relay).

For diagnostics only! you could probably use a fused jumper to the FP relay 12 volt input (the inertia switch wire) and your own ground to the FP relay and see if the car starts under its own power. That tells you for sure that you are tracking down the only known issues.

There are ways to fix it but fixing it right might take a little more work.

Good luck.

DNeinstadt said:

I have NO ground other than the bracket holding the FP relay. Manual ground from test port to frame is only way I get ground on tan wire. Suspect: bad/missing ground from computer.

Click to expand...

Yep.

DNeinstadt said:

I'm also not getting ANY power to/from inertia switch and/or FP red wire. That makes me suspect the EEC relay and/OR the computers ground. Both of which are hard to determine. So I am pulling the EEC's relay next and testing ports on that. I am not familiar with the TAB/TAD, or ISC, how would one test those? That sounds easier to do!

Click to expand...

The computer supplied ground should have nothing to do with the EEC relay - think of them as separate systems. They only work together on your FP relay since the EEC relay supplies key-on 12 volts to the FP relay and the puter supplies ground to the FP relay (both on the control side of the FP relay to energize its coil).

An easy place (for me) to see about EEC power is at the WOT relay. It is under the air inlet tube on the pass side. It is a normal relay so check for one terminal being key-on hot there. If it is, that sounds like the EEC relay is supplying power to at least the WOT relay.

JR can sum this all up a lot more concisely than I can. I have a pretty good understanding of the circuits but it takes me longer to think of how to phrase things than it does to physically test stuff.

A fresh start is often good too.

Good luck.

Pardon me while I step in for a sec Hissin.

Dan, at the EEC relay check the Red wire (I'm betting it's zero since you have nothing at the intertia switch). Also check the BK/O wire (should be 12v if the blue link is good). Check the R/LG wire for 12v with the ignition in RUN (should be 12v). Hoping the wire colors match.

And you're right about the 90 being a bastard stepchild when it come to some wire colors. I think Ford ran out of the correct stuff.