Hi fellas. After searching for some time now (here) I can't seem to find the answers I am looking for.! I recently had my head machined back to factory specs because of exhaust valves being a little sunk. We noticed this during a head gasket replacement. Head was machined as well just to be sure. The car never overheated. It was pushing coolant under boost. Now that that has been fixed and my head is basically new I am having a sputter after 200-250 miles on new plugs. Using proper gap .26 or so. The car recieved a fresh tune after the work by the super Evo genius Ron at RS motors in Burnsville Mn. I am running E85 with supporting bolt ons and a old school fp green that is still pulling strong. I put new plugs in and viola! All is good for a couple hundred miles ot so. Then like clockwork the past 3 sets of plugs they start to sputter/buck at mid rpm's all the way up. Example: start a full pull in second gear at 2500 rpm's or so and at roughly 3800-4200 rpm's the car will sputter and buck. Drives fine in all other conditions except lower rpm pulls. Another example: Driving 70 mph and drop her into 4th and put the foot down. Again the same result. None of which happens prior to the 200 mile mark on the plugs. Check the plugs and they are a bit black on one side and not the other. All consistantly irregular in color. Car has 40k on her and is a 05 Mr. It has never had these issues. Any ideas would be great. Thanks in advance fellas and ladies. Merry Christmas, Rick

 

I have also tried moving the gap up and down from .22-.28 all of them had the same result above.

 

sounds alot like mine, but i dont have clue to whats causing it.

 

.26 is very huge gap maybe you mean .026 which is still huge. Black plugs mean rich AFR which causes fouling.

 

afr guage? what are your ratios like both while cruising and then under WOT ?

 

What plugs are you running? You may want to try a plug that is a step hotter.