computer problems

[rocket7824]

I just swaped bodies on my two 91 explorers, but did not swap computers. after about 50 miles of driving my cel came on and it started to run rough. my question is is it the diffrence in the computers or do i have a bad computer

 

[MrShorty]

I suppose either one of those scenarios (differences in computers or bad computer) are possible. However, there isn't nearly enough information given to know. A couple of suggestions:

1) When the CEL comes on, that means the computer wants to tell you what problem it is seeing. I think the best first thing to do is pull codes and see what problem(s) the computer is seeing. If you want to try pulling codes yourself, review my "notes on pulling EEC-IV trouble codes"

2) Regarding the differences between computers, do you know if there is a difference between the computers? I don't know how many different "computers" Ford put into a '91. Obviously if one was an auto tranny, the other manual, they would have different computers. I don't know how many different calibrations Ford supplied. Best way to know if there is a difference between computers is to look at the part number and calibration code on that should be attached to the computer. If the two computer have the same codes, then there should be no difference between the two. If they have different codes, then there may be some minor differences, and we can explore that possiblity.

 

[rocket7824]

koeo codes 51,53,54. koer codes 98,54 53 51. I had no problems with this engine in my other truck, only diffrence is computer and body wiring harness. hope this helps.

 

[MrShorty]

51 refers to the ECT signal, 54 refers to the IAT signal, and 53 refers to the TPS signal.

Because KOEO faults are set when the engine isn't running, they are almost always electrical in nature.

ECT and IAT are basic thermistors. TPS is a basic potentiometer. They all feed off of the 5V Vref signal generated by the PCM. Perhaps somewhere in that wiring, you've mis-connected (is that a word??) the Vref wire that feeds these three sensors.

 

[rocket7824]

so if it is not getting the 5 v from the pcm the computer is bad perhaps?

 

[MrShorty]

Perhaps, but don't get ahead of yourself. Computer do go bad, but not very often. Usually, a bad computer is diagnosed by process of elimination. You test every other possible cause and, if everything else checks out ok, then the computer must be at fault. You haven't even begun to diagnose any of the other possibilities. Do you have a wiring diagram and a DVOM? Start with those and check for Vref at each of those three sensors. If you aren't real skilled at this kind of diagnosis, I would suggest locating a good repair manual (I've seen them at libraries) where you can get a copy of the circuit "pinpoint" test for each of those codes. This will lead you systematically through the diagnostic tree for each of those codes.

 

[rocket7824]

The only reason i think it is the computer is all the sensors stayed on the moter when i changed out the bodies. I also had problems before i changed bodies in the body that is on the truck now. thats why i think it is either the computer or the harness.

 

[rocket7824]

Ok I replaced my pcm with the one off my other truck (thank god for great dads- he took it out and sent it to me) and unpluged and repluged all connectors, dont know witch one fixed it, but only code i get now is 11 which is system ok. Now i have another problem. I have a terrible miss I think. Just put new plugs and wires on it today. Checked my coil pack it read 1 ohm on all the primarys so thats in the tolerance. The secondary checked at 14k ohms, the tolerance for that is between 6k and 11.5k ohms. Is that reasonable? I also checked the ignition modual. Everything checked out alright except the resistance on the crank possition sensor. It was supposed to be 2k to 3k ohms and it was 600 ohms. Any ideas. I'm thinkin either the cps or the coil pack.