Re: Replacing distributor with an HEI in a MPI 4.0?
I must add that the 4.0s distributor doesn't do anything regarding timing. It's a disstributor only timing is set in the computer. It uses the CPS as a TDC mark. Load (MAP), rpm (CPS), temp, O2, and throttle (TPS) are input on which the computer decides the timing and fuel amount. A HEI wouldn't make any difference. 4.0's are not notorious for cross firing or weak sparks. The HEI brings a CJ ignition on the strength of an original XJ ignition.
Your problem might be a wrong distributor. Do you run a 4.0 distributor? If not, yours is adding advance on the advance it allready gets from the computer. Twice the advance should cause some severe pinging!
I guess you used the entire electronics from an XJ or Wrangler with TB, computer, harness and O2 and (almost) everything. Where is your CPS? On the bellhousing or on the pully? What kind of dist you have? The original 4.0 has no advance mechanism in it.
Keep us informed.