Alright here's the skinny. I have a 1990 4.0, Cherokee. I have spark, fuel, and the motor just turns over and won't fire. Could the timing have jumped that bad ? Don't know what's going on . I must say I am perplexed.

 

compression? bring the #1 to TDC on the compression stroke and check to make sure the pointer is on the #1 position on the cap...that will tell you if it jumped timing....

 

you say you have spark.. do you have a spark plug plugged in to the spark plug wire and holding it to the motor block?

ppl say they have spark but the actual plugs are bad.. maybe replace the plugs with new just to be sure their not fouled

 

Yes, I have spark. I pulled the plug out, hooked it back to the plug wire and grounded it to the block. It sparked but not as fast as it should have. You know how it should spark in rapid succession, well, it sparks but really slow. I'm trying to get as much out of this thing until I have to drop in the 95 4.0L I have for the Jeep. I am just not looking forward to putting an HO motor in place of the Renix. It sounds like it is going to be a PITA. I was just hoping you guys may have experienced this before. I am a mechanic by trade, I'm a retired AirForce Jet Engine Mech/ Acft Maint. I have an A&P license and all that useless crap. I just don't have alot of time around the 4.0 L. I truly appreciate any input.