I replaced the coil with a used one and car ran great for about a week. But now its back. Do you thing it was a fauly coil? Or perhaps an injector?

Fyi plugs are new.

 

It's possible. Why don't you swap that coil with another cylinder and see if the code changes to the other cylinder.

 

I had my car parked up for awhile and I forget the basics lol. Thanks Dennis

 

Here are some misfire troubleshooting basics. 1. swap the plug with the plug from another cylinder and see if it moves. while you have the plug out you can see a lot of things. You can see if its burnt, if the cylinder is getting too much fuel or too little for that matter.

2. Check the ignition wires if the miss does not move. they may look ok but may be cracked and causing the spark to ground out. I would spray the wires with water while the car is running as well as the coil and see if you see any arching or sparks.

3. If all appears ok you may need to do a compression test and see if your cylinder is not sealing properly (bent valve ). PM me if I can be of any assistance.

Best of Luck

 

looking to see what was the outcome of this issue

 

I love it when people answer their own questions... Was it a gray dot coil? If not do some research on the forum here and you will know why...

 

Used coil I got from buddy is fine. I didnt realize he swapped 4 to 6. His used coil went into 6. Did a test and 4 is now gone (not the used one I got). I guess I might as well order a new set and change em all.

 

If you have a misfire it is most likely spark plug or coil. The ECU and wiring hardly go bad.

 

This seems to be more serious. Changed coil 4 yesterday with new coil. Light went off right away. I guess after driving (prepping for emission test) and a 8hr cool down. Car is throwing p0304 again in pending. Car started rough this morning but drove fine. Going to have to take it into a shop as I have no time to diagnos further.

 

Also now get P0420. Test O2's. Rear O2 is dead. Could this or even a bad cat cause misfire?

 

P0304 just went on its own again. Not showing as full or pending code now and car starts fine. Changing dead rear O2 today. I have until Tuesday the latest now to do a drive cycle and have car ready to pass emissions

 

So now it seems as if the P0304 issue is only on cold starts. After 5 minutes of driving it goes away!!

 

So I let the car idle. Drive slowly not to trip a code and passed emissions tests. However this is still an issue on cold starts.