i have a 2012 Harley f150 with 6.2 i just bought it and get terrible mpg it came with roush exhaust,cai kit , toyo m/t open country mudder tires 33/12.5/22 . im showing 10.6 mpg on dash

 

The first thing I would check is if the odometer is accurate.

 

Not surprising with those mods and tires.

 

Yep. If the tires are taller than stock and the PCM has not been recalibrated, you are going a greater distance than is being recorded

 

I have an '11 Lariat with the 6.2 in her. I'm running the stock size rubber, 275/65-18. I have the Stainless Works long tube headers, X-pipe, high flow cats and the Stainless Works performance exhaust. I'm also running an SCT Livewire with custom performance and tow tunes. On my trips out to West Virginia from Delaware, by tune: Stock/SCT 93P canned tune I regularly average 19.5-20.5 mpg or so at 65 mph.. All my custom performance tunes weather 93P or 91P average 18.5-19.5 mpg. Once I tried an economy tune, but we won't go there.....Been deleted. So, The trip average usually ends up being around 17-17.5 mpg once I arrive. That's a 265 mile trip, starting out on mostly level roads. Then about half way I get into the hilly roads then mountains. In bad, windy (crosswinds), rainy weather it suffers. Now, around town is much different. Most of my "'Round Town" driving consists of short 10 mile or less trips to the P. office, market, Walgreens, etc.. On those, yea-----11-13mpg if I stay out of it, 10-11mpg if I don't. When I go to visit my nephew, he lives about 35 miles away. Most of the trip is rural roads and small towns. On my MPT 93P I average 14-16mpg. On the SCT 93P canned tune I do the best at 17mpg, but that's if I STAY OUT OF IT, nice weather, etc.. Over all average last time I checked was around 13.5-14 mpg. Now that we are into winter blends, it really goes down. My last trip out I was getting just 9-10 mpg on my errands.



A trip out to West Virginia





I was running on the MPT 93P tune this trip





Halfway point was at about 134 miles, so now I am on the down swing.

 

are my tires bigger than stock to make that difference

 

Look how much heavier your current tires are over the stock ones. Typically the stock tires are in the 39 pound range. Now add in the difference your odometer being off causes and you're probably close to what your numbers show.

 

I'm sure the OP got the answers he needed by now, but for future reference, I just bought a 2011 SCrew Platinum 6.2 2WD with stock sized wheels and drove 600 miles to get it home from the dealer.

I averaged 15.0 MPG @ 80-90 MPH for the trip; sometimes bumping the 100 MPH limit (ECU would start modulating engine power around 96-ish). This was on the onboard computer set at the 5 minute interval, and MPG was confirmed with hand calc.

Still just under half on my second tank of gas and the onboard computer now shows 14.2 without resetting, just putting around city streets approximately a mile or so round trip from home to the TMC 4 days a week.