The exact thing happened to me when I side gapped my plugs, decrease in fuel mileage. And just to be sure that it was not caused by me I tried 3 different sets of plugs with different amounts trimmed off on each set. Went back to a new set of stock plugs and the fuel mileage was back to normal so I thru the iridiums back in which I had been running for the past 2 years and mileage remained normal. All these tests were done using brand new Nology coils and wires.
