First time turning the key: Fuel pump won't prime/run

Discussion in 'Fox 5.0 Mustang Tech' started by 1990Coupe, Oct 18, 2008.

  1. I was under the assumption however then you could simply get a computer/engine/headlight harness from a matching year V8 car, and swap those out and you'd be OK.

    I think something is missing though between the 4cyl car stuff, and the v8 engine stuff i just added.
  2. I had a similar prob with my camaro. the pump wouldnt prime. I replaced the pump and all the fuses and still no prime. I finally ran a jumper off another fuse and wired it to the fuel pump so the car would run.

    this is just me, but I would temporarily keep your jumper in place and solve what is keeping your car from idling. It could be that you have missed a ground somewhere or that a clip has come undone. hell it could be anything, I am just speculating now.
  3. The 4cyl has 2 fuseable links,1 fuel pump relay.1ecm relay.
  4. tonight im going to try to trace fuse able links. i think the one i need to be concerned with is on the driver side by the starter solenoid. I found 2 diagrams from t-moss.. It seems like in 1991 there were 2 different engine harnesses???!?!?!?!



    WHAT THE HELL! :mad:

    Attached Files:

  5. WTF does all that stuff mean??? lol...I've never been able to understand stuff like that.

    When my black car was still the running 4cyl it used to be it had a relay under the drivers seat, right on that cross bar. I left it there when I swapped the V8 in it. I used a 1992 engine harness, computer, and headlight harness. I had two relay my the MAF. I swear I also had one tied into the harness above the ECM in the kick panel. It's been two years, so that's the only one I'm not 100% on, but I'm 90%. All the wires on the selenoid together correctly? Did you have the carpet and seats out?....Do you think something stupid happened, such as the relay falling under the carpet or anything?:shrug:
  6. I never had the carpet or driver seat out, but i can tell you there is no relay under the driver seat. I do have the relay on the passenger side kick by the ECM (thats the ecm relay) and i only have one relay on the passenger side shocktower by the MAF. the car is a 1991 and all harnesses are from a 1991

    Something doesn't add up. The 4cyl to 8cyl engine computer harness support matrix must be wrong. It seems to me like there could be 2 different engine computer harnesses for a 1991. can anyone confirm WHEN the FP relay was removed from under the seat to the shock tower?
  7. Dude, I would bet a buck fiddy that the puter is bad. Sounds just like my 89GT did. It wouldnt start and after testing I foun no power at the pump. I ran a wire, got it fired and it would run for a couple seconds @ 600-800 rpm then sputter and die. Took the day to figure it out. My ECU went bad from moisture as I had a small rust hole in the door jamb right abouve the computer :nonono:
    Open up the ECU and see if you have any signs of moisture in it. Also find a buddy with another Stang and borrow his puter to see what happens :shrug:
  8. I think that it could be the computer too - but where the heck is the FP relay??

    I'll have to wait until the weekend to get a computer to swap in. Wouldn't the engine NOT run if the computer was bad? i can feather the throttle to keep her running if i needed to, and i was able to keep her running by doing that - i did have some backfiring through the intake though.
  9. You DID check the inertia switch, right?
    Oh, and here's a simplified diagram of the engine harness where the fp relay should be..

    Attached Files:

  10. According to that link (thanks BTW) i should have the relay under the seat, as far as i knew - i didn't. Tonight i will pull out the driver seat in search of this relay.
  11. That relay does not exist on my engine harness. only the WOT relay. Which means there should be one under the seat, i did not see it unless its hidden under the carpet. My car was unmolested when i got it, so i can be almost positive that the driver seat has never been removed. That leads me to believe that my car is either different the most 91's or the friggen title has a misprint on the year and its really a 1990 :shrug:

    Attached Files:

  12. There is only one plug instead of the 2? Are you sure you got the right engine harness?
  13. That relay mounts to the front cross bar where the front seats get bolted to. There is a hole in the carpet. The wire comes up through the carpet under the seat and has a plastic clip that pushes into the metal floor (through the carpet) Pulling the seat out and the left sill plate will help you life the carpet up just to see if it got tucked away.
  14. yes the car is a 1991, and the harness is from a 1991. i got the harness from 25thmustang and he assures me its from a 1991. All that i have read about this engine harnesses has me believing its definitely from a 1991.

    I doubt it got tucked away just because the car hasn't been touched..

    From what i can see is i have a 1991 car with no FP relay under the seat. i will take the seat out and see if its under there but i doubt it.

    Ford moved the FP relay under the hood an 92-93. I think i may need a harness from a newer car although im not sure.

    God this sucks.
  15. Man, this ****es me off, and it's not even my car.

    I really hope you get it running. I don't have any 92-93 harnesses, hell, I don't have any year harnesses. IF I did, you know I'd ship one to you to try, for the hell of it.
  16. Sorry. Got my years mixed up. It should be under the seat. Have you checked the inertia switch in the rear panel to make sure it's good and also not popped?
  17. Yea man it has me really bummed.. I knew something was really wrong when i put the key in, turned it to the "run" position and the horn began to go off.. For some reason i have a horn issue and i needed to unplug it cause with the key in the run/on position the horn just goes off :(:(

    Yes i checked the switch - its not popped. I also checked for voltage - i got nothing coming in or out of the inertia switch with the key in the run position.
  18. How many connectors do you have on the driver side shock tower that connect the dash harness to the computer harness? You could have one or two plugs. Also, you might want to look into the horn issue first. You might have a wire that is grounded. Also, there is a difference in the dash harness between the 4cyl. and V8 harness. Been there done that. As most have said about the relay under the seat, it's not that somone has messed with it. It's the fact that the 4cyl. cars went with the FP relay in the ccrm and not under the seat. That does not mean the wiring/connector for the FP relay is not there. You need to verify that. Also, when you look under the seat don't confuse the connector for power lumbar with the relay connector.
  19. As you've seen, since you removed the I4 harness, you need to find the FP relay pigtail from your donor harness or create/splice together a pigtail for the FP relay.