Hey all,

I was reading a post about a 99 F250 with a V10 wondering about fuel mileage and some posted that they were getting 14mpg with a V10. I would actually love to get that with my super duty. I've had it since November of 2010 and the best that I have ever gotten was 9.8 mpg. I drive sensibly between 55 and 60, use cruise cont. alot. I shift around 2000 RPM'S and don't beat it what so ever.

A little history on the truck: 99 F250 super duty, 5.4 gas, 5 spd, 4WD, 4" lift with 35x12.50x16.5 tires. The truck has roughly 108,000 miles on it. I know smaller tires will help and I actually need tires so I'll be getting new one later on this month.

Any other insite to the problem would be greatly appreciated.

Thanks
Scott

 

Are you up to date on maintenance? Spark plugs being the big one. If not swap them out for some E3s. I've always noticed an MPG boost when E3s were swapped in. Also just check for other misc fuel burns, like exhaust leaks, clogged filters (Air, Fuel.. Etc).

 

The lift & tires are definitely not helping.

But, I've noticed with mine that cruise control actually hurts my mileage. There's one interstate stretch of a trip we take that I can get 17mpg if I don't use cruise. Using cruise I get 13.

 

Another thing you didnt mention was what gear ratio you are running. Were they changed for the tires size difference just asking. It does seem like more work for that tires size and a 5.4L

 

Add 9% to your miles covered since you have oversized tires. Your speedo is off causing you to get erroneous mpg readings unless you've corrected it. if you have 3.73 gears install 4.56 or 4.88 to recover some additional mpg since your engine has to work harder with the poor gear ratio.

 

With those 99 2V non PI heads, Id also be looking at changing the setup. Maybe going to a set of PI heads and cams(Will raise compression). Or even looking at doing a topend Navi swap for the 4V heads, cams, intake, etc. This will also pick up the power production by a good little bit as well.

 

Hey, thanks for all the good input, I really appreciate it.
I'm not sure the gearing in the axles in overdrive what I think is 55 or 60 the RPM's are roughly around 2000 or 2100 as far as plugs go I haven't changed them yet but am planning on it. I was also wondering about the idle air control. It seems sticky, when I come up to a stop sign it seems to idle really high and takes abit to come down to idle. Let me know what else you think could be the issue.

 

The IAC is a cheap replacement. If that doesn't fix the hanging idle, then check for vacuum leaks and check that your TPS sensor is adjusted to read .99 volts at idle. You can loosen the bolts and turn the TPS sensor alittle bit to get it dialed in perfectly. You will need a way to datalog in order to do this though.