cherokee90

I have a 90 Cherokee where is the computer located on them? I think mine may be bad and got a free one from a 88 so y not try it.

5-90

Look under the IP, down by your right knee.

It's just difficult enough to replace that you don't want to do it very often - the screws are difficult to reach. What are your symptoms? Why do you think it's the ECU? It's good that you got a replacement gratis (I'm assuming the condition is "worked when pulled?") but figure it's going to take the best part of an hour to dismount/remount the ECU, unless you have rather small hands.

(It's only three screws, but three screws that are a pain to reach...)

Also, you should note that the automatic and manual versions are different - the connections are the same (the TCU is separate - on the other side of the IP, under the glove box, behind the lower trip,) but the fuel injection and timing curves are slightly different due to the extra requirement of running the slushbox.

So, what are your symptoms? It may not be the ECU after all, and I'd like to save you some work if I can...