[DEEZ PLEEZ]

A freind of mine has a 1991 Mustang convertible that he is in the process of bringing back to life. the car originially came with a 5 spd and he swapped that for an AOD. he did change over the ECU upon doing this. currently, when he turns the key to the on positioni the fuel pump is not pressurizing the system. the pump does work because
that was able to be jumped off a battery to make sure it works.
i think it's a relay however, where is the fuel pump relay? he says that he has checked and tested a relay under the drivers seat but i don't know if that is the correct one. could there be any other problems that either one of us has over looked? if i left some info out sorry, just ask and i should be able to get whatever info is needed to help you solve my problem

[DEEZ PLEEZ]

sorry,

it is a 5.0L

[luniticlizard]

The relay under the seat is the correct fuel pump relay.

What did your friend do with the clutch pedal switch. I had a friend who did the same thing and he left the clutch pedal and switch in it. When you wanted to start the car, you had to depress the clutch to close the switch, even though it was an auto.

He might want to look into that, if he hasn't already. Perhaps the switch is open. I would see if there are any trouble codes as well. They always help point you in the right direction.

[coolwaterblvd]

U can push the switch in and tape it really good because the car will not do anything if the neutral saftey switch is open. Also just replace the relay under the drivers seat because the pump should come on the even with the neutral safety switch open. Pull the relay out and see if it smells like it is burned. If it is burned the pump is still bad even thought it comes on wired directly; it is pulling too much amps and will just keep on blowing relays which are like 25$ a piece. I have checked put pumps that are reading 0.00OHMS which is a short to ground but would still come on.

[DEEZ PLEEZ]

thanks guys. i'll have him check that stuff out. i will update as soon as i know something.

[DEEZ PLEEZ]

ok. back to the drawing board. the relay has been changed, the fuel pump is new, and there is voltage back at the pump. for whatever reason when the pump is plugged in it will not work. any ideas??

[coolwaterblvd]

Check out the plug itself u might need to bend the contact points so u have a complete circuit also put on some die electrode grease.

[DEEZ PLEEZ]

ok. i'll pass that on. thanks!!

[DEEZ PLEEZ]

does anybody know how the ECU is grounded?? my friend was able to get a wiring schematic and make the pump work by bypassing the ECU.
what we are thinking at this point is for whatever reason the computer is not properly grounded thus it is not completing the circuit. please keep in mind that i have not physically seen the car yet. i'm trying to do this over the phone. thanks

[meangreen92]

Originally Posted by DEEZ PLEEZ

does anybody know how the ECU is grounded??

The main ECU ground goes to the negative battery terminal. Someone may have replaced the terminal or cable, and just attached the EEC ground wire to the body or something.

[DEEZ PLEEZ]

thank you. i will relay that to my buddy. i think this car has bigger problems but w/o being able to put my own eyes, ears, and hands on it, i don't know what's going on.

[nakternal]

I hate to beat a dead horse (no pun intended) but when all the usual suspects in the fuel pump circuit check out fine and theres still no power, make sure to check the inertia switch.

[DEEZ PLEEZ]

i was not aware that these cars had one. is it located in the trunk
or the passenger kick panel? i know that those are the two common locations that Ford used.

[romeo5.0]

I am having the same problem right now. I just pulled my ecm out of my 88 and pin #20 was burnt i havent bought a new ecm yet but i have narrowed out everything else in the car. Im just nervous about buying a computer because if somehow it is something else i dont want to waste all that money. But take a look at it.

[DEEZ PLEEZ]

thanks romeo. i'll have him check that out.