New spark plugs, worse mpg

Bought truck used and just did a tune up after driving it a year. 92k miles and it had the original plugs in it. Mpg avg before was 18.5 mixed. The old plugs were worn to about .050 to .060. Gapped new plugs to .043. I bought the oem densos from the dealer. Installed a new oem air filter also. I have filled it up twice since the new plugs. Now getting 16.0-16.5 mpg. Wtf gives?

 

Try resetting the ECU?

 

Do you know when the MAF sensor and Throttle Body was cleaned last?

That's an easy one to do and is never a waste of time. I don't know if the new/better spark is related to that via the ECU making new adjustments to your air intake... it's worth a shot and 1.5 hours of your time anyway.

 

Bigger gap = more thorough of combustion = more efficiency = better gas mileage. I always gap my plugs as wide as I can without having issues. As long as the rest of your ignition system is good, go big. Manufacturers set the gap in a neutral zone of efficiency and reliability. If you don't mind a few days of testing, find where your maximum gap is (goes for any car) and you will have max fuel efficiency and power. You won't hurt anything on your truck.

 

I know this seems sort of counter-intuitive, but when I filled up my truck with Premuim (93) after cleaning the MAF and throttle body I got about 16mpg. When I went back to regular (87) about 3 tanks later I jumped to 17.something. To some people's taco it doesn't make a difference, to others premium runs better. For mine, the cheap stuff is the way to go.

Didn't know about that, I may have to remember that when I change out my plugs soon.