91' F-150 Computer Problems
 

My dad got in his truck one day and the truck would not start. After some trouble shooting we discovered the fuel pump was not running and there was no spark. The fuel pumps are good, it would not energize the fuel pump relay. More digging turned up a totally fried computer, I mean burned up bad. I am scared to buy a new computer, I'm afraid it will do the same thing. If anyone has ever experinced this or knows what could be wrong please let me know. Any help is greatly appreciated.

Have just had the same thing happen to mine. No power from ECU to fuel pump. ECU fried. Was told by F truck spares salesman that I had to check for an electrical short and if none was found then a reco computer would be ok. ( mechanic stuffed my ECU in my opinion ).
I'm not an auto electrician so maybe a senior user can offer more advice.

The general consensus in the majority of threads is bad grounds for electrical problems. Your grounds can never be too good.

Next would be direct shorts to ground via a piniched or abraded line.

There are capacitors that go bad. (Do a search here.)

I believe you can send your ECU/PCM for repair or diagnosis. But not sure where.

Last, I would guess would be testing individual components.

Pehaps some one here will provide a flow chart for you to follow.

Good luck.

Sounds like we have other problems to solve before we plug in another EEC Module.

With the computer unplugged we need to find out why you do not have any spark.
Turn on the key and see if we have power at the Ignition Coil Positive side (+). If not we need to check fuses and fuse links.
If we have power move your test light to the other side of the coil and crank the engine, does it flash? If not we need to check the TFI module, Ignition Coil and the pickup inside the distributor.

At any rate we need to have spark before we try another EEC Module (computer).

Is it possible that something went wrong in the ignition and caused the computer to fry? Does the computer control the ignition or is it seperate? I now have the truck at my house so hopefully this week I can really get into trouble shooting this truck, by the way thanks for all of the advice that has been given. It will come in very handy this week.

No but you may have some open fuse links. Explain what you mean by fry, did you take it apart and it is all black inside or did the truck just stop running. Both but while cranking the computer is not controlling the spark and you will have spark while cranking without the computer in the truck. It would be the same as if you had pulled the SPOUT out.
It will not start because the injectors will not be firing.
Did you read my post above?

The computer is FRIED it looks like it burnt a capacitor on the board. I read your post just wasn't sure how it worked. Thanks for all of the info though, it should make the trouble shooting go better.

The capacitor you are talking about in more than likely one of the bigger filter capacitor for the 5 Volt Supply. Capacitor will do this on their own and the capacitor may have shorted the 12 Volt input to ground and taken out the Fuse link supplying the EEC power Relays contacts. If so this would be why you have no spark, check for 12 Volts at the + side of the coil with the key on.

I do have power at the coil with the key on and my test light does flash on the other wire when I turn the motor over. My brother had the truck before me and said he had the module in the distributor checked and it was supposed to be good. Subford, thank you for all of the help and direction you giving me on this problem.

If you have power on the + side of the coil and the other side is flashing you should have spark, if not change out the coil. That is all a coil needs to fire the plugs.
Try sticking another coil wire into the coil and check to see if it arcs to ground. Hold it with insolated pliers.

Okay with a new coil we now have spark. I have a friend that is supposed to bring me another eec. Should I try it or should I start looking to see if there was cause for this one burning up?