FAQ:

Possible PCM.Powertrain Control module electrical “issue” on a 1988 ford f150?

Thanx in advance for any help with this I’ve been dreading the mysterious electrical probelem for along time now and it finally hit….started when it would rain..truck ran like crap and it took about ten minutes to get her running smooth..been that way for a while…one day after a night of heavy fog I went out to start it..nothing..long story short.I had no spark.I replaced the coil, magnetic pickups and eec module, cap, rotor, eec relay, fuel pump relay…checked all the wires everything seemed fine…turned her over and with a lot of hesitation she started… ran for about 5 minutes and just shut off…we fiddle with stuff cheched for power ..no spark…no fuel pump…hmmm.. to make it clear ..I started out with no spark and now I have no spark and no fuel pump…..but we were both suspect of the fuel pump operation to say the least. I could hear it click on when I turned the key but once you start to turn the truck over or it starts you can’t hear it….but I know I’s not getting spark cause i checked it with a timming light I used to time the truck when it DID start earlier that day.. funny thing is it started, ran for 15-20min then shut off. like someone turned the key.. checked buch of stuff …turned key… started, ran for 5 min shut off . hasn’t started since….so the Q is there any way to test the power control module or any thing else I should be looking for?I’ve been at this for a few days now and it’s really starting to wear me thin. it wierd..the truck has spark, starts up perfect, runs smooth as could be for 5 minutes, then shuts off…no spark….pull the plugs, check wires, test ohms, volts, things seem ok, get her running again…boom shut off…so it seems I have an electrcal problem with power to the ignition and power to the fuel pump.could this be the “PCM”?like I said thanks again for any help!!!

Answer by helpful bob
The thing is that vehicle is so old the wires will end up rotting/corroding not just where they connect to but internally.From what you’re saying it sure sounds like you’ve some type of sensors/connections or wiring that is being shorted out by moister especially if it started when it rained.I’d go over all the wiring harness’s both under the hood and under the vehicle look for anything that maybe frayed/damaged or cracked or bare or subject to moister/water.

Any of the old connections such as the grounds can act up bec of the weather or extreme temperatures so check all the ground junctions bec any major sensor ground even can mess up the system, especially fuel pump grounds.Get yourself a full ground local chart and ECM diagram/schematic sometimes part source has these diagrams that they’ll print out for free, just don’t forget the ignition and fuel system schematics.Autozone.com has some schematics for that vehicle so look on their site bec I found a few on there for it myself just now. Note the sensors are usually grounded via a common ECM ground circuit and the grounds going to the ECM could be faulty.

Hope that helps and best of luck.By the way those old wires really can end up rotted inside and changing the grounds and other wiring may help but it also does sounds like you could use a good original factory service manual or manual.Plus from all you say it could be a faulty ECM bec I’ve seen and heard of them causing many weird problems and shutting the engine off is one of them.Note if you’ve any relays in the fuel pump system or shut off control valves these could be also causing your problem.

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