I recently change my spark plugs on my 2000 GMC Sierra 1500 Z71. I Replaced them with ACDelco Platinum, same part number(41-952). A Couple of weeks after replacing them the truck started to run rough, so I pulled the plugs to see if something was wrong there. Turn out two spark plugs had cracked insulators between the terminal and the treaded portion. Since I still had the old ones, I threw those back in and went back to the parts store to get replacements. Turns out the part number had changed so the gave me new plugs with different numbers. I got home and compared them to the original plugs. Turn out the electrodes on the plugs with the "new" part number do not go into the engine as far as the original part number parts. I have been to several other parts dealers with the same results, none of them have the original part number plugs. So in the mean time the truck was running fine with the 6 new plugs and the two old plugs, until a couple of days ago. It started running rough again, so I again began to pull plugs. Two plugs were again cracked in the same region, and came from the _same_ two cylinders as the first two cylinders that had the cracked plugs.
Okay now to my questions:
1) Are the different electrode lengths a problem??2) Is the fact that the all 4 of the cracked spark plugs came from the same
2 cylinders a sign of a more serious problem??Thanks
Lou