ggbwg

Hello all, I replaced spark plugs 6 weeks ago, with ac delco iridium plugs. 120,000 miles on the car, no issues so far. I am getting random p0301 and p0304 misfires. I can only feel the misfires at idle, the car is still running great, getting same mpg as before the miss. I haven't changed the coils yet, and i have tried seafoam in the last tank of fuel. I am wondering if the new plugs and old coils are my issue. Any help would be appreciated, thanks all.

Oldblue

Check the wiring harness connections to the coils!

RJ_RS_SS_350

Hi GG, to the forums!!

If the misfire is new, starting after you changed plugs, I would be swapping plug 1 with 2, and 3 with 4, and clear the codes. If you get new codes, P0302 and P0303, then you have 2 bad plugs. If the codes do not change, I would be swapping coil pack 1 with 2, and 3 with 4, clear the codes, and check again for new codes as above.

If you had these same codes before the plug change(sounds like this is not the case), go straight to swapping the coil packs as above.

ggbwg

The miss was not present before changing plugs. I will swap the plugs and coils after the rain stops this weekend. Thanks for the advice, will let you all know how the drama unfolds!

donbrew

Did you try to "gap" the plugs? Never touch the whisker on a iridium plug, they are pre-gapped.

ggbwg

No, never touched em, just installed. They are quite sensitive plugs. Thx

Oldblue

Just an idea, as it has happened to me before, are the new plugs AC 41-103's??

ggbwg

Yes, they are. Hence you had trouble with those?

Oldblue

No , those are the correct plugs, I bought 4 at my local parts palace , bellied up to the counter , gave him the Year, make model engine size , transmission , told him the 41-103 AC Delco number, was distracted by an old friend in the store, got home noticed he gave me 41-105's!

That's why I asked, sometimes the computer parts books are wrong!

donbrew

41-105 are correct for 2006 models. 105 is slightly hotter than 103