starting problem
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New User
Joined: Jun 2004
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starting problem
Help!!!!!! I Have A 91 F150 That Doesn't Want To Start. Problem Has Been Intermittent For Some Time And Now Seems To Be Full Fledged. Started Out As Just Going Dead Driving Down The Highway. After Some Time It Would Start. Changed Ignition Module On The Distributor And Fuel Pump Relay. When I Turn The Key On The Fuel Pump Relay Sounds Like Morse Code, Replaced It But Still No Joy. I Can Get The Truck Started Sometimes After Trying For About Ten Minutes But When It Starts It Is Running Real Rich. When I Turn The Key On The Pumps (dual Tanks) Just Keep Running, They Don't Shut Off And The Check Engine Lite Stays On. Bought A Reader But That Doesn't Tell Me A Thing. Have Heard Everything From Computer To Fuel Pumps. Took To Ford Once After It Acted Up And It Cost Me 100 For Them To Tell Me It Was A Good Truck. Any Help With This One I Would Appreciate. Thanx
Tuned
Joined: Apr 2003
Posts: 394
Likes: 13
From: 13th Colony
The fuel pump should run for a couple of seconds when first turning the ign switch to run. If it continues to run, either the fuel pump relay is sticking, or the computer is telling the pump to stay on (maybe bad comp or comp thinks engine is running). There is no other reason for the pump to stay on. Are you sure you replaced the fuel pump relay and not the ECU (computer) relay? They are mounted side by side. I think the fuel pump relay has a green plug on it and the ECU is black. If you can not get the computer to give you codes, then I would have to say you have a bad computer. The computer should tell you why the check engine light is staying on.
New User
Joined: May 2004
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I just got my 90 running today ('bout time too) and I threw this up on another post, so try this...
First try unplugging the vacuum line from the MAP sensor then try starting truck - mine would at least run but rich.
Second unplug the the electrical connector from the MAP sensor then either reattach the vacuum line or leave it plugged - mine started again but still ran rich ( at least it was running though).
I replaced the MAP sensor and everything works fine, I just wish I would have replaced it before the ECM >
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First try unplugging the vacuum line from the MAP sensor then try starting truck - mine would at least run but rich.
Second unplug the the electrical connector from the MAP sensor then either reattach the vacuum line or leave it plugged - mine started again but still ran rich ( at least it was running though).
I replaced the MAP sensor and everything works fine, I just wish I would have replaced it before the ECM >
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computer location
am going to change the computer on my 91 ford but where is it? pulled one unit and parts store looked at me like i lost my mind. someone said it is on the passenger side under the dash? thanx in advance
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
On my truck, when you pull the vacuum line to the MAPS, the truck dies immediately. I don't know why yours would run without it connected.
The computer is near your left foot while you're driving. I think it's on the firewall on the inside of the cab.
The computer is near your left foot while you're driving. I think it's on the firewall on the inside of the cab.
Tuned
Joined: Apr 2003
Posts: 394
Likes: 13
From: 13th Colony
buddy,
There is a 10mm bolt on the engine side that holds the wiring harness to the computer. Loosen the bolt and then pull the harness back. The computer is held down on the inside with a bracket under the driver kick panel. Remove the bracket and then pull the computer out from the inside. There is a dust boot/gasket around the computer, be sure to put it back in when you put the computer back in.
There is a 10mm bolt on the engine side that holds the wiring harness to the computer. Loosen the bolt and then pull the harness back. The computer is held down on the inside with a bracket under the driver kick panel. Remove the bracket and then pull the computer out from the inside. There is a dust boot/gasket around the computer, be sure to put it back in when you put the computer back in.
Posting Guru
Joined: Jun 2004
Posts: 1,781
Likes: 1
From: Central NY
Hi,
I was just thinking that maybe you have more than one problem.
The dual tanks had a recall as one tank would try to fill the other tank so that may be why your pump stays on.
The intermittant problem sounds like a power problem to me, like the computer was loosing power, and if it stayed off for like 10 minutes I think that would clear the codes too. I would check the 5v and grounds at the computer.
I was just thinking that maybe you have more than one problem.
The dual tanks had a recall as one tank would try to fill the other tank so that may be why your pump stays on.
The intermittant problem sounds like a power problem to me, like the computer was loosing power, and if it stayed off for like 10 minutes I think that would clear the codes too. I would check the 5v and grounds at the computer.
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Tuned
Joined: Apr 2003
Posts: 394
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From: 13th Colony
Popa, the recall on the tank was a result of the selector switch/valve not functioning properly. I don't think it had anything to do with the fuel pump running all the time. If the pump is running when the engine isn't, the relay has to be on, that is the only way it can get power.
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Posting Guru
Joined: Jun 2004
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From: Central NY
Hey Bronco,
I see that the original post said the pumps would run continuously when the key was turned on. Do they not shut down when their is adequate pressure in the line? Which is what I always thought...
If not, why do they shut down when the engine is not started but the key is on? Some kind of startup sequence initiated by the computer?
Popa Tim
- never to old to learn something new -
I see that the original post said the pumps would run continuously when the key was turned on. Do they not shut down when their is adequate pressure in the line? Which is what I always thought...
If not, why do they shut down when the engine is not started but the key is on? Some kind of startup sequence initiated by the computer?
Popa Tim
- never to old to learn something new -
Tuned
Joined: Apr 2003
Posts: 394
Likes: 13
From: 13th Colony
Popa, there is not a pressure sensor on the fuel rail. The computer has no idea whether there is pressure or not. The program tells the fuel pump to run for a few seconds when you switch ignition on to build up pressure. I think I just figured something else out. The turning of the distributor is detected by the tfi (control module) and that tells the pump to run. I found that by turning the distributor with the ignition switch on, the pump will run a few seconds, you turn it again, it will run again.