94 Computer into a 91 truck

[redranger4oh]

I have a truck with the engine and harness from a 91 explorer that I swapped into it. I just finished swapping the auto out for a manual. For the transmission swap I used the computer and transmission out of a 94 explorer. I am able to start and drive the truck, but both the tach and volt guages don't show anything. Also, when idling the truck starts to sputter and and will die after about 30 seconds. I am guessing that the issue is that the computer is not compatible with the engine, but before I go trying different computers, I figured it would make sense to ask around here for some pointers. Initially I thought it might just be the computer having to reset itself, but I have driven it around for about a half hour and it doesn't seem to have changed anything. Also, I made sure and plugged the vacuum line that used to go to the auto. Thanks

Dan

 

[fireguy12117]

There are differences between computers 91 and 94. is the check engine light on? if it is, start there...i would imagine that it should be though and if its not, double check that its not burnt out.

i am little confused with what you did!? according to the title though you basically have a 94 computer on a 91 motor, in which case there are a few differences in the sensors used over the years. i discovered this when trying to replace my 93 PCM with junk yard finds before i knew there were differences- the major one i found was gen 2 (your 91) seemed to have a combo of BAP and MAF sensors, the gen 3 (your 94, my 93) went solely with MAF sensors. i got my information from reading Haynes and Chilton manual electrical diagrams so if i am incorrect, I’ll have to revisit the diagrams.

i don’t recall exactly if there were differences between explorers and rangers in that same regard (different sensor set ups in the same year btween ranger and explorer) but i think there might be. Also, i never got more detailed info about differences such as different fuel trim tables to account for the extra weight of a sploder.

i've never been convinced that swapping PCM's works and i still run rich even with a 93 PCM made for a 4.0/auto which is what’s supposed to be in there.

if you can get the part number of the PCM, you can google it and with a little searching you can find the year, and set up for each PCM and try to match up whether your PCM is looking for a sensor that’s just not there. i had a 91 PCM run my 93, but it sure ran like poop...