This is follow up to a question I posted a couple of months ago but
can't get to anymore for some reason, and google doesn't allow you to
respond on an old thread.

Found Here:
http://groups.google.com/groups?hl=e...com%26rnum%3D1

Ok guys thanks for all your help, but the problem came down to the
computer. I bought the engine, wiring harness, and computer from a
salvage yard and was told that I was given an engine from a 94 YJ no
problem right? Well after pulling many hairs we went and got a book
on the Grand Cherokee (we had a hunch) from a friend and were able to
identify the wiring harness and computer as a Grand Cherokee's by the
color codes on the wires. The Grand Cherokee has that security lock
system which of course my Jeep does not, so the computer was turning
off the system because it could not find the key's chip. Very
frustrating. I called the salvage yard and was less than diplomatic
but I got the right computer (I found it myself) for no additional
charge, and now my YJ runs quite well. So once again thanks.

Oh and for anyone considering a 4.2L to 4.0L swap, DO IT! However
save yourself some headaches and just figure on getting the swap kit
from Hesco. I was trying to be cheap and it ending costing me a lot
of time I could have been four wheeling. The price isn't really that
bad and they are EXTREMELY helpfull.

Mike