My fuel economy has taken a dump lately, figured it was time again for some maintenance. I replaced the plugs around 95k, I'm at 135k now. The NGK iridium I had put in before we're toast, gaps were worn to over 55 thousand. The active plugs were just a mess again(yes DOD is still active on my car). I gave these NGK Ruthenium Tr5ahx a try, they are more costly but whatever the others didn't last 40k so I wasn't going to use those again. Did the valve cover gaskets, upstream O2 sensor and coils as well. Car for sure runs much smoother, hope that relates to an increase in fuel economy only time will tell. On a positive note the valve covers were clean as could be, Mobil 1 changes since new every 5k is the reason.

 

 

Wow, that's clean.

I did plugs in my LS4 years ago, not iridiums and a set of MSD wires. Last year had a slight misfire, random cylinders. Swapped back to iridiums 90% better. Swapped back to AC Delco wires 100% better.