Originally Posted by stir_fry_boy
I put NGKs (yes, they were the correct NGK number) in my XRS instead of Densos. My car didn't like them much and started missing with CEL code P0401. I changed them again to Densos and the problem went away. For some reason my original plugs failed at 66 K in cylinder #1 only.
Seems strange that your #1 plug failed.. and then you replaced it and then got a P0401 (which is a #1 misfire code).
Makes me wonder if there is something else going on... possibly a failing coil or something.
If the P0401 comes back swap the #1 and #2 coils and clear the code. Then drive it until you get a code again. If it's still a P0401 then something else is going on. If it's a P0402 after swapping the coils then the coil at #2 is bad.
Then again it could just be coincidence. #1 plug failed and then the NGK plug you put in #1 just happened to be defective. I can almost guarantee this has nothing to do with the fact that you used NGK plugs though.