1991 F150 ecu problems?
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4wd Low
Joined: Nov 2025
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1991 F150 ecu problems?
5.0 motor 5 speed
Running terrible! Couldn’t even drive. Will start but very erratic idle or dies. If you give it any gas it backfires. Motor making weird noises.
hooked up an ebd1 tester and got no error codes, everything passed. Then the strangest thing is that I turned off the tester but left it hooked up, and the truck ran perfect!
ChatGPT says this is a ground issue, the meter is acting as a ground. Had me test continuity of all engine ground and battery wires, plus wires to the tps, and mapp. All good. ?????
I zip tied the meter in place and I can drive it just fine now, but I know this is not a solution
Anyone have any ideas??? Computer ?? I don’t know what else to check. If I disconnect the meter the truck barely runs. Thanks for any help!!
Running terrible! Couldn’t even drive. Will start but very erratic idle or dies. If you give it any gas it backfires. Motor making weird noises.
hooked up an ebd1 tester and got no error codes, everything passed. Then the strangest thing is that I turned off the tester but left it hooked up, and the truck ran perfect!
ChatGPT says this is a ground issue, the meter is acting as a ground. Had me test continuity of all engine ground and battery wires, plus wires to the tps, and mapp. All good. ?????
I zip tied the meter in place and I can drive it just fine now, but I know this is not a solution
Anyone have any ideas??? Computer ?? I don’t know what else to check. If I disconnect the meter the truck barely runs. Thanks for any help!!
Fleet Mechanic
Joined: Oct 2025
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From my understanding, test mode runs off a “base” tune taking out any signal from the sensors except the ones it’s testing. I’m surprised you’ve gotten no codes from it. That could be completely wrong, but could account for why it runs that way. If I’m correct that means that it isn’t actively feeding from map, IAC, O2, etc. have you pulled the computer to look at the board?
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4wd Low
Joined: Nov 2025
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No. I only bought the truck about 6 months ago and don’t know the history. Of course it was running fine when I bought it, but upon inspection I can see that the battery, alternator, tps and o2 sensor had been replaced, I’m guessing trying to fix this intermittent problem.
Is it tough to pull the board and what would I be looking for?
Is it tough to pull the board and what would I be looking for?
Fleet Mechanic
Joined: Oct 2025
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https://www.ford-trucks.com/forums/1...ral-years.html
Really good pics in this thread. Removing the computer is easy, it’s behind the driver kick panel. Be careful removing the harness connector(done from under hood), it can be brittle. All you have to do is unscrew the case top and you’ll see the board.
Really good pics in this thread. Removing the computer is easy, it’s behind the driver kick panel. Be careful removing the harness connector(done from under hood), it can be brittle. All you have to do is unscrew the case top and you’ll see the board.
Last edited by 90project5.0; Nov 25, 2025 at 06:29 AM.
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You said you get the system pass code for KOEO and KOER tests? Spending $300 on a “new” computer hoping that fixes it is crazy to me. Did you at least remove the ECM to look at the circuit board?
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4wd Low
Joined: Nov 2025
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I’ll do that first and see what it looks like. I think the only test that came up but went away was something about “spout”??
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Fleet Mechanic
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The spout is the little plug you pull to set initial timing and then put back in. Is that there? Removing it or it being broken removes any computer advancing.
Last edited by 90project5.0; Nov 25, 2025 at 11:31 AM.
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Fleet Mechanic
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Last pic, look at the blue/green cap. It was rust/oxidation look on it. That computer case alone looks corroded. If it were ME, I would get another one. That’s me. The pics aren’t the clearest, but the one cap for sure looks suspect.
