Possible Bad Engine Control Module
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Junior User
Joined: Jan 2007
Posts: 84
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From: Virginia
Possible Bad Engine Control Module
My truck is a 1990 F150 with 4.9. A couple days ago my starter went out. It seemed to have shorted out, when I cranked the engine over it would not engage and after a couple seconds the electrical system shut down. No power to anything with the key on. I knew it couldn't be the battery but I put the battery charger on anyhow. I eventually set the charger to boost, 50 amp, to see if I could get the engine to crank over. When I went to start it again the power came back on and it tryed to crank again, this time when it stopped and the electircal system shut down again and there was smoke from the engine compartment. I replaced the starter and reset the computer and it started up and ran. Now the engine runs rough when first started and cold. After warming up it misses once in a while. I pulled the codes and have two, 536 (Brake On-Off) and 632 (Overdrive Cancel Switch). I have a feeling that I fried the computer, does anyone have any suggestions. Don't think either of these codes have anything to do with the engine running the way it is. The way it is running reminds me of first starting up the truck after the computer has been reset but it runs like that all of the time. It does run good 55 and above, doesn't seem to be missing then.
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Junior User
Joined: Jan 2007
Posts: 84
Likes: 0
From: Virginia
Can't get the computer out, any suggestions? I have had it out before with no problems but now I can't get the connector off and the location of it makes it difficult to get a grip of it. The connector is in the firewall and you can't get a grip on it to pry it off.
Elder User
Joined: Feb 2002
Posts: 504
Likes: 2
From: Saddle Brook United State
The computer plug should back out when you loosen the bolt holding it to the computer, that is unless you cross threaded the bolt. The plug is connected to a wire harness and is not attached to the firewall in any way, after the bolt is all the way out you should be able to move the plug out of the way slightly. You shouldn't have to do any prying. The computer is held in with one bolt and a plastic clamp. I have a 90 and have removed the computer several times looking for a problem similar to yours. Getting it back in is a little tricky , but if you lube the weather seal with soap it slides right in without folding the seal. It turned out to be a burned capacitor (47 mfd -16 volt) on the computer board. The bad cap was easy to detect by looking carefully at the vertical electrolytic caps. There are several of these on the board. I replaced the cap and repaired the damage on the board and the problems are gone. See the post----https://www.ford-trucks.com/forums/746958-i-think-its-the-computer.html---for a picture of a burned cap.
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