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. If you are not familiar, I am working on a 4>8 swap. The car is a 1991, and I got and engine, computer, and headlight harness for a 1991 v8, so i assumed all i would have to do is swap everything out, and fire her up.

    Today was that day. I did a search, and I ran some tests. At the ECC port on the driverside firewall, i jumped the fuel pump and grounded it. Still no prime. Checked for 12v at the ECC fuel pump port when the key is on and i get .99 volts. At the rear of the car, the inertia switch has not been tripped, and i have NO power going to either wire going into the switch.

    Now here is where its tricky, I have NO relay under the seat, and only ONE on the passenger side shocktower with 4 wires going in??!?!?!? I figured since i have on on the shocktower i should also have one under the seat and this is not the case. I jumped a long wire from the positive on the battery all the way to the line on the fuel pump and i got her to fire and stall, but at least fire.

    Any ideas? it was a huge letdown after 4 months of work. :(
  2. The one and only relay i have on the passenger side shock tower has this part number..

  3. But how can I be "missing" the fuel pump relay?

    This circuit has nothing to do with the Headlight harness does it??
  4. Anyone :(

    I was reviewing wiring diagrams in my manual and they are no help. Im ready to rip out all of the engine/computer/headlight wires and start over.
  5. Isn't there a fuel pump relay behind the glove box? I remember on my friends 90 LX 4cyl, there was. The new auto parts store had it in stock. Check that too Justin.

    Sorry about the news. I know you'll figure it out. Do you have all the grounds hooked up....Firewall....two on the left fender apron(behind battery) and the two on the rad support?? (one on each side) I know, those are obvious, but I just though I'd ask. the computer grounded on the inside kick panel??
  6. I have all the grounds hooked up. I double checked them. I do know that in only have one relay on the passenger side shock tower and nothing under the seat. I was unaware that i would have a relay behing the glove box? I'll have to check that.

    I will also have to double check the grounds.
  7. I checked behind the glove box since its not in yet, i have no relay behind there.
  8. This maybe way off but the same thing happened to me.4 to 8 swap , all new wiring from same year cars, 1993 in my case, turned key and no prime.It turned out to be the ground curcuit in the computer. Check to see if you can set the TPS switch voltage. If you cannot find ground there then it may be the ground curcuit in the computer.That is how I found out my computer was bad.I changed it out with a known good computer and it all worked fine.The computer provides a shared ground for all of those curcuits to operate. Also, You may only have one relay on the shock tower only.,Mine is that way,again it's a 93. Good luck, Dan.
  9. FWIW, on earlier aero V8 foxes, there is but relay on the passenger strut tower (it's the WOT relay). The FP relay was under the drivers seat. In later aero years, the FP relay moved from under the seat and next to the WOT relay. Four bangers might have had something like a CCRM, which would house the FP relay.

    The EEC relay on all aero foxes is above the EEC in the passenger kick panel.
  10. OK so basically I can try to set my TPS sensor. If im reading no voltage, then there is a chance i have a computer ground/ computer issue? I'll have to check that when i get home.

    What is the CCRM? Everything from the 4cyl was retained except for the Computer Harness, Headlight Harness and Engine Harness. I got confirmation that my engine harness is a correct 1991 model, and yet i only have the one relay on the shock tower. This would lead me to believe i have another relay in this "CCRM".

    Would a Bad EEC relay cause this fuel pump issue as well? Remember i rigged a wire from the positive on the battery, TO the fuel pump. She fired but kept stalling and wouldn't hold an idle, BUT she fired.
  11. I was trying to help another guy with an 88gt with a 5.0.the 4cyl has 2 power supplys and the fog lites are involved.i can help more later im at back look 4 need help
  12. OK i just googled CCRM.. When the car was a 4cyl it was on the passenger side shock tower. I removed it because it went with the 4cyl computer wiring. the v8 stuff didn't have that giant relay box or needed it..

    Any other ideas?? Here is what the 4cyl configuration looked like before i removed it, you can see the CCRM which was part of the 4cyl wiring.

    View attachment 296365

    Here is the car before i took it apart. you can see the old CCRM in the right of the picture.

    Attached Files:

  13. I will search for it - but when you get home please let me know! :)

  14. I found that thread -

    First problem i have is that there is no relay under the driver seat- i only have one and its on the passenger side shock tower. Unless there is some hidden one, or the 4cyl has some wierd wiring and has it hidden else ware:shrug:

    I did the fuel pump test with the ECC diagnostic plug - First off the wire for the fuel pump which comes into the plug has .99 volts when the key is ON. That tells me its before that plug possibly at a relay which i can't locate.

    Boy this is tuff.. haha
  15. so the ccrm is completely disconnected and removed?
    That controls the fuel pump as well as a host of other devices on the four cylinder car.
    your new 8cyl harness should have taken care of that though. ....... what was the verdict on the ECU?
  16. Like you said - all 4cyl computer wiring and headlight wiring have been removed that includes the CCRM as it was part of the 4cyl computer harness

    The ECU is an A9P, and as far as i can tell its working? Not to sure how to check if its not working. By manually getting the fuel pump to turn on with my ghetto wire, the engine would not hold an idle. Something charastic to an unplugged Mass air sensor. The car would like idle at 800 rpm, choke and die. Maybe i have a computer issue?
  17. yeah that would be the first thing I look at next. do you have one that you can use?
  18. No i don't :(

    What about this - What years did the stang come with the FP relay under the seat? Some i have read that in 1992 they moved to the shock tower. My car is a 1991 maybe 4cyl's are different and didn't have one under the seat, meaning i'd probably need a harness for the computer from a 1992+ car. I found these 2 links.

    Fuel Pump Relay Issue 1993 Mustang LX - Ford Mustang Forums

    This guy has a factory 1991 V8 and has a relay under the seat
    Bypassing Fuel Pump Relay - Ford Mustang Forums

    I'm thinking maybe one needs to be wired in?
  19. I have fords wire diagram at home the 4cyl is wired different,as 3.8 is also another.