Pontiac Repair: 1996 Sunfire, spark plug gap, coolant temp

Question
Help!!!  My sunfire, which I absolutely love..or did until recently has begun to have problems intermittently.  It will run fine and then sputter and try to staul.  When this first happened, there was actually a fire in my exhaust.  Plugs, wires, O2 censor, fuel filter have all been changed.  Lucas injector cleaner has been added.  Nothing has helped.  Someone suggested that one of the coil packs may be bad.  My son seems to feel that this isn't the case as there is a steady and constant spark.  The catalytic converer has been bypassed as well and that wasn't the problem.  Any advice or information you could offer would be greatly appreciated.  It is a 2.2 litre/

Answer
Hi
I would check and see if it did not jump time.
A fairly common occurance on a 2.2.
I would check your spark, kv, it's ability to jump a spark plug gap.
I would ohm out the coils. I would check the towers for rust/corrosion.
I would also check and see if there are any codes stored in the computer.
I would have the data observed and see if the TPS is constant and steady. I would check MAP, coolant temp sensor and IAT for proper readings.
These are just basics I would start with.
I would though REALLY concentrate on TIMING since the backfire out of exhaust.
If it was actually  fire, it MAY be dumping fuel /no spark.
It then ignited in the exhaust, either by heat or a backfire spark.
I would REALLY concentrate on timing.
Pawl