Misfire cylinder 4 (P0304)

[StuckChuck]

2002 Pontiac Bonneville SE. I was about to head to work, when I started the car, it sounded terrible. Bad missing, and some backfiring sounds at the valve cover area.

I recently changed plugs and wires, they were looking pretty rough. Replaced with AC Delco professional plugs, and Duralast Gold wires. It ran fine for a few days. In fact, it seemed to run better than it had in the year I've owned it.

Anyways, after the misfires, I checked the codes and got the P0304, misfire cylinder 4. I checked the plug, it looked good, it did have a bit or dry black on it, possibly from the misfires. I changed the plugs around. Same problem. Changed plug wires around, changed coils around, changed fuel injectors around. No change at all, still the same code for the same cylinder. Sounds the same as well. I do know that the coil was sparking, although I'm not sure how much it is.

I've changed both the water pump, and battery in the past couple of months, just due to different reasons. Ran fine afterwards. This just started suddenly a few days ago. I am at a loss as for what to do. I only own this one car, and I need to get it fixed to make it back and forth to work. My entire livelihood rests on being able to figure it out. Any suggestions on what I should do next? I appreciate it in advance for your assistance.

[AnthonyK]

Sorry you're having trouble, I know the feeling of having to greatly rely on having one car. Sounds like you started with the right things to check and switch around to isolate it to cylinder #4. I dont think you could have accidentally put the wrong wire on the wrong plug if it ran fine after changing plugs ??. The next things I would check is the ICM (ignition control module) that is under the coil packs..could have gone bad. Could also be a malfunctioning crankshaft position sensor. Do you have good fuel pressure ?

[StuckChuck]

I triple checked the wires. I am unsure about fuel pressure. I believe it is okay, as all other cylinders work fine. I suppose it could be an icm. I have no way to the junkyard to get one yet though.