hi there gals and guys i am new to this forum and looking for help i have a 1991 jeep cherokee that runs fine for days on end then all of a sudden will not start it seem to fire and die then after i leave it for a time sometimes it will start then run for days on end fine then do the same i have changed the pcm which seems to work but after a time it fails i then put the old one back in it runs fine so i dont think thats the problem any hints as to what it might be thanks

 

Welcome.
Posting your vehicle details helps since approach to your problem could be different.
This ' no start' is very very (very) common thread on this forum, and I think that doing a search will give you a lot of ideas.
Yes,we can go over them, but getting some ideas yourself and do some basic testing will not only give you more insight in this problem, but will also be helpful for us trying to help you.

The basic rule of a no start is: finding out if you have a no spark situation or a no fuel situation (or both).