I bet this will stump you as it does me..

[skyhigh350]

Thanks for the link. I am using the 90' engine in the 91' eclipse. With the 90' ecu.. I will check the link.

[niterydr]

Alright.
So what did you do about the cas sensor? That is different at times as well.
You'll want to swap on the 91 cas, 91 tb, 91 transistor, and then move a few pins in the ecu.
Go to http://www.dsmchips.com/1990ecu.html for more info on the ecu stuff.
I don't think it is on vfaq anymore, sorry for the bad link.
Your best bet?
Swap in the 1991 ecu (if it is a good ecu, check the caps). And also swap in the 1991 transistor, coil pack assembly, tb, and cas