misfire

[MasterofDisaster]

About a week ago my 08 NA GT was stumbling and running rough. I replaced the plugs, and it ran better, but still had the roughness. On the way home CEL illuminated, and the scanner said P0303 cylinder #3 coil.

Just installed 8 new coils this morning, and it's still running rough with a little misfire. Indeed, I thought I heard a backfire. I stopped and checked, and all the electrical connectors are firmly attached to the coils.

Is there any sort of engine analyzer that would tell me the source of the misfire? Do I just have to wait for a code?

 

[Juice]

You already determined it is cylinder 3.
You changed plugs and coils, problem still present.
Do you have fuel going to #3, is the plug wet with fuel?
Do you have good compression on cylinder 3?
Must have all three for an engine to fire:good mechanically, have spark, and have (the right amount of) fuel.
Try a different coil?

 

[MasterofDisaster]

Thanks, Juice. I should check that.

I did not notice that plug 3 was wet when I changed it. I thought it was a little darker than the others.

When AutoZone gave me the printout last week, I took it to mean that the coil was bad. They probably should have a standard suggestion to check the coil, rather than imply the coil should be replaced.

CEL illuminated again tonight, and again it came back to P0303, misfire cylinder 3. I'll have to look some more.

 

[Juice]

When my daily 4.6 2v loses a coil, I always do coil and plug. Tried just coil, it never worked.