1991 F150 Fuel Pump Won't cut off Won't Start
#16
04-30-2008, 07:30 AM
#17
04-30-2008, 05:29 PM
#18
04-30-2008, 09:00 PM
the ecm/eec is located behind the kick panel on the drivers side. Right where the e-brake pedal is. If you still have trouble locating it, follow the wire harness to where it goes through the firewall. It will have a 10 mil. bolt holding the rectangular wire connector to the computer. It is probibly a 60 pin connector so you should see 60 wires entering the fire wall into one clip. The computer is silver about 8" long 11/2" thick 5"wide.the harness clip is on the engine side of the firewall and the computer is in the truck. I believe the computer should have a sticker on it that starts with E8TB-12345-Z2B or something like that. This number is different for each year, stae, options,cam shaft, emissions, etc. so make sure you match the number or the truck will not run right.
Hopefully this works for you. Let me know the outcome.
Hopefully this works for you. Let me know the outcome.
#19
05-30-2019, 12:09 PM
Had the same thing going on, after several months of beating my head against the wall and trying everything I could find, I came across your post and decided to check the fuel regulator. With the key on and the pump running, I pulled the vac. hose from the unit, no changes. Then just for the hell of it I had my pliers in hand and I gave the valve a little tap on the side and the fuel pump stopped. Turned the key and fired right up, even with the vac. hose off. So I got a can of WD and squirted in the port and reattached the hose, been starting fine ever since! Might have to replace the regulator eventually, but a lot better than searching for electrical & computer problems!
#20
05-30-2019, 06:32 PM
Same thing was happening to me.
Had same problem, finally found out a light tap on my fuel pressure regulator stopped the pump and allowed me to start my 91 4.9. Sprayed a little WD40 in the vacuum port and hasn't missed a start since.[QUOTE=Dmartin_1;3578657]Sorry But my fuel pump run all the time and the truck wouldn't start pluged the vacume line up pump stopped running and truck started right up. I just done this last Tuesday.[/QUOTE]
However, mines got the 4.9 and only the one tank. It only happens every once every three or so days, not every time I drive the truck.
Anyway, heres what I have done so far, when the truck gets cranky the fuel pump runs and wont allow me to start. I pulled the FP relay and checked it with 12V, the coil pulled in like it should, contacts cycled. Then I checked the terminals in the fuse block where the relay plugs in at and it too had 12V, but in order for the coil to release inside the relay the 12V has to go away. According to the book the EEC has a timer in it that after a second or two opens up the ground and drops out the 12V to the fuel relay, dropping out the coil and interrupting the fuel pump circuit, killing the pump. I checked the fuel pressure @ the fuel rail and had 50PSI, that was witht he pump running(And truck not able to start).
After about 10 minutes of tinkering the truck decides to allow me to start, and the 12V going to FP relay drops to @10V thereby allowing the coil in the relay to drop out and allowed the truck to start. It really sounds like an EEC problem to me, but I dont want to just strat throwing parts at it until I find out exactly which one it is. What do you guys think?
Also, I have checked the EEC relay,and it worked, even swapped the FP and EEC relay, did the same thing.
I have two questions, on the timer in the EEC, is it a strait timer or does it look at other things before it opens up and cuts power to FP relay?
Also, I know the fuel pump in my truck os old and the check valve doesnt work right(As pressure drops off to almost nothing when it stops running) But when it is running I read ~50PSI at the schrader valve. Could this make a difference?
Anyway, heres what I have done so far, when the truck gets cranky the fuel pump runs and wont allow me to start. I pulled the FP relay and checked it with 12V, the coil pulled in like it should, contacts cycled. Then I checked the terminals in the fuse block where the relay plugs in at and it too had 12V, but in order for the coil to release inside the relay the 12V has to go away. According to the book the EEC has a timer in it that after a second or two opens up the ground and drops out the 12V to the fuel relay, dropping out the coil and interrupting the fuel pump circuit, killing the pump. I checked the fuel pressure @ the fuel rail and had 50PSI, that was witht he pump running(And truck not able to start).
After about 10 minutes of tinkering the truck decides to allow me to start, and the 12V going to FP relay drops to @10V thereby allowing the coil in the relay to drop out and allowed the truck to start. It really sounds like an EEC problem to me, but I dont want to just strat throwing parts at it until I find out exactly which one it is. What do you guys think?
Also, I have checked the EEC relay,and it worked, even swapped the FP and EEC relay, did the same thing.
I have two questions, on the timer in the EEC, is it a strait timer or does it look at other things before it opens up and cuts power to FP relay?
Also, I know the fuel pump in my truck os old and the check valve doesnt work right(As pressure drops off to almost nothing when it stops running) But when it is running I read ~50PSI at the schrader valve. Could this make a difference?
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