This is a 1996 MC with the 3.1 engine. The car was throwing codes P0171 and P0300. The symptoms started with the car not idling smoothly and longer than normal cranking to start intermittently when fully warmed up. This progressed to a no start condition when fully warmed up, then try to restart.
After an hour of cooling off, it would again restart. It always started and ran cold. (This is with average around 40 degrees at the time)

Replaced the upstream 02 sensor, no change.

The fuel pump was the problem, and had to be replaced. It was not able to maintain the correct pressure as it warmed up after operating for 25 to 30 minutes. (I had a mechanic troubleshoot this for me) It would drop the pressure just enough so the car would run, but poorly. The fuel filter was replaced also.

Hope this helps anyone facing the same issue.

 

A good rule of thumb in a random misfire, if the plugs and wires check out okay, check your fueling.

 

Don't forget about the coils too. Watch misfires on the scan tool and if you see 1/4, 2/5, 3/6 dropping together, replace the proper coil.

 

It is quite rare that a coil goes bad (from what I've seen) but yes a good point

 

More often than you think. Seems like Chrysler vans are the worst though.

 

In the case of GM coils, yes, I agree. I've work on enough of GM's modern engines (that use the same coils) and maybe ONE out of 100 happens to be a bad coil.

 

This is a Monte forum, my information is basically only related to GM stuff

Chrysler stuff just falls apart without reason