son has a 1998 jeep cherokee sport straight 6. He replaced the gasket and filter on transmission and now it will not start. It turns over but acts like it doesn't want to fire. Held down gas pedal to see what would happen, slight fire almost like backfire, then nothing but turning over. Are there any vacuum hoses he may have unknowingly unplugged? other things to check?

 

Check the connector for the crankshaft position sensor, located on the transmission bellhousing.

Without that sensor input, you will have no spark and the engine will absolutely not start.

 

its pouring rain right now n we're under a tornado watch but I did manage to pull the code. Then it started, rough but running. P0320. I think you're right TJ, I'm going to check that as soon as this storm blows over. Thanks! He did say that its ran rough and stalled in the past so I'm thinking maybe the actual sensor

 

P0320 is "no crank reference at PCM", so this really points to the crankshaft position sensor circuit.

Good luck and keep us updated!