My mom just bought an 89 yj with an MPI conversion in it.
It appears to be running a bit lean. I think they all do.
Does any one know where I can find the documentation for this setup on the web? Does any one have a copy of it.

I do, but im leaving for school right now so e-mail or PM me and I'll get it to you tomarrow. Its somewhere around here. :D

Just treat it like a 1994 YJ 4.0LI
f it were mine, I'd replace the O2 sensor on the exhaust manifold. When these go bad your fuel mixture can get bad also.
Studying the spark plugs are the best first step in determing an off kilter fuel mixture. Check for manifold leaks too.
It is wise to make sure a 'check engine light' is installed with the MPI kit if this wasn't done.
After the MPI is installed, there is no documentation needed other than a factory manual, including the check engine light blink codes. The blink codes will tell you when the system needs some help.
The fuel mix is adjusted by the computer so if everything is in working order then there isn't much you can do except to take it to a Jeep dealer and hook it up to their computer for diagnostics.
I've been told a tecnician can 'tweak' it a little. I believe the timing can be adjusted by 4 degrees.
If you will go to my Jeep web site (below) you will find links to the MPI installation instruction manual on the HESCO site plus a link displaying all of that system's error blink codes and how to activate them.
If you need a diagram of how to install the check engine light, just let me know and I will try and scan it for you.

My Jeep Site (http://www.monsterslayer.com/jeep)

Thanks for the info guys.
Rockbuggy I got the email.

I think I will be replacing the 02 sensor to see if it does antything.
The spark plugs are telling the tale of a motor ran too lean.

The jeep does have a check engine light on the hood.

What about the spark plugs?

Originally posted by Rocktoad
What about the spark plugs?

Try Champion RC-9Y-C4 plugs gapped at .035" They are one step colder.

Plus, you are probably exeriencing the classic MPI "lean & ping" syndrome. Sometimes this can be somewhat cured by having a dealer tech or someone else with the equipment retard the computer the timing by (the max.) 4 degrees.

The other alternative fixes are expensive ....
1. Install an adjustable fuel regulator from HESCO $ 185.00
2. Install a 4.0 head $ 300.00 - $500.00*
*This is the absolute best mod you can make.
It fixes the lean/ping and adds mucho HP.

Notes:
1. A 4.0 head install usually does not need the adjustable fuel regulator.
2. Some sucess has been had by going up one injector size.
... those from a 5.0 if I recall correctly ...

Hmm I have a 5.0 motor sitting around the house maybe I'll try them injectors in moms heep.