?Computer Problem or Something Else? Help!!!
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Joined: Aug 2004
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?Computer Problem or Something Else? Help!!!
I have a problem that I have made no progress with. I have recently purchased a 1988 F-150 4WD Supercab with 351 engine and auto trans. It will crank and run normally and idle for as long as you let it. If you take off up the road with it or pat the accellerator, reving the engine, it will run fine for a while and all of a sudden shut off as if you have turned the ign switch off.
When driving it, the harder you drive it, the sooner it quits. The computer is shutting it off, but why, I do not know.
I know this sounds like a classic fuel pump problem, but the fuel pump is only quiting because the computer is disconnecting the ground to the FP relay coil and probably the FI also. After sitting for a few minutes, it will crank and run fine, but the same way (idle forever, but not run log if driving or reving the engine.
I have already done these:
1. replaced the eec and fp relays
2. checked eec pinouts for voltage and/or resistance
3. checked several sensors by disconnecting. I got error codes on sensors that I unhooked, but I had no error codes before.
4. the truck has duel tanks, but with either tank, its always the same.
5. when it shuts down, I can ground the fp relay coil, (where the eec is supposed to ground it, and the fp runs, but will not run on it's own untill after it sits a few minutes with the ign off)
6. the previous owner gave me a new coil and ign module, but putting them on made no difference.
7. I bought a rebuilt eec from autozone, but it also made no difference. (I realize that this kind of problem may be somewhat of a "weakest link" problem, and may be something that a rebuilder may not find)
8. I have tried to find a good used computer, but it has not been easy to come by in my area.
9. I have checked wiring, fuselinks, put on new battery cables.
10. All wiring seems to be in good condition.
Everything I check points me back to eec, but I hope someone who knows more than I do may steer me in the right direction. If you can give me any info as to where I need to check and hav'nt already or can direct me to somewhere where I might find the info I need, I would appreciate it.
When driving it, the harder you drive it, the sooner it quits. The computer is shutting it off, but why, I do not know.
I know this sounds like a classic fuel pump problem, but the fuel pump is only quiting because the computer is disconnecting the ground to the FP relay coil and probably the FI also. After sitting for a few minutes, it will crank and run fine, but the same way (idle forever, but not run log if driving or reving the engine.
I have already done these:
1. replaced the eec and fp relays
2. checked eec pinouts for voltage and/or resistance
3. checked several sensors by disconnecting. I got error codes on sensors that I unhooked, but I had no error codes before.
4. the truck has duel tanks, but with either tank, its always the same.
5. when it shuts down, I can ground the fp relay coil, (where the eec is supposed to ground it, and the fp runs, but will not run on it's own untill after it sits a few minutes with the ign off)
6. the previous owner gave me a new coil and ign module, but putting them on made no difference.
7. I bought a rebuilt eec from autozone, but it also made no difference. (I realize that this kind of problem may be somewhat of a "weakest link" problem, and may be something that a rebuilder may not find)
8. I have tried to find a good used computer, but it has not been easy to come by in my area.
9. I have checked wiring, fuselinks, put on new battery cables.
10. All wiring seems to be in good condition.
Everything I check points me back to eec, but I hope someone who knows more than I do may steer me in the right direction. If you can give me any info as to where I need to check and hav'nt already or can direct me to somewhere where I might find the info I need, I would appreciate it.
Lead Driver
Joined: Feb 2003
Posts: 8,140
Likes: 4
From: Oak Harbor, OH
There are 3 fuel pumps on your truck. There is one low pressure pump un each tank that pushes fuel to the high pressure pump on the frame. I would change the fuel filter first, if that doesn't fix it then I'd go after the frame mounted pump.
Lead Driver
Joined: Nov 2002
Posts: 9,555
Likes: 40
From: Concord, NC
Yes, definitely check that high pressure pump. After it cuts off, turn the key back to the on position and listen for the fuel pumps - this is easier if you have someone to lay under the truck and listen for them while you turn the key. They should come on for about 2 seconds after you turn the key to on. Does the tach (if you have one) still register rpm's when the truck stalls? Another possible problem area is the coil, but I see you replaced that and the module already. I don't think this is a computer problem.
New User
Joined: Aug 2004
Posts: 2
Likes: 0
My truck is somewhat different, yet maybe this info might be of some help. I have a 94 F150 6 cylinder with a 4.9 engine. My truck was operating in just about the same manner. We changed the fuel filter, and was about to tackle the fuel pump (located inside the fuel tank), when lo and behold we found it to be the EGR valve. First we removed & cleaned & reattached the EGR valve. It ran great, but not perfect. Thought maybe it was the EGR sensor (attached to EGR valve) or the EGR solenoid. But we met a machanic who assured us it was the EGR valve. So we bought a new one ($80.) and YEAH ! Its perfect!
Senior User
Joined: Jun 2004
Posts: 291
Likes: 0
My 87 302 did that once. It started shutting off and on while at speed. It finally wouldn't come back on and I had to pull over(on the narrowest shoulder in the county).
After popping the hood I happened to stumble across a short in the lead to the ignition. I only found it because it was a crimped connector that came apart when I touched it.
It was caused by a little rough handling by a young mech. installing a new battery at a local tire shop.
It was fine until the wind started blowing on the wire through the grill. That particular wire was cut and respliced about five times along a 2 foot length. Probably from previous owners attempts to add accessories.
After popping the hood I happened to stumble across a short in the lead to the ignition. I only found it because it was a crimped connector that came apart when I touched it.
It was caused by a little rough handling by a young mech. installing a new battery at a local tire shop.
It was fine until the wind started blowing on the wire through the grill. That particular wire was cut and respliced about five times along a 2 foot length. Probably from previous owners attempts to add accessories.
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