Ive had two trucks do this now. the first was 05 5.4 crew cab, the only thing done to it was duals and drop in k&n... it was wrecked around 65k miles and replaced with at 06 5.4 crew cab that has a gryphon, lt headers, highflows, x'd duals, efans, and cai. Both trucks have had a significant loss of mpg around the 60k mile mark. idk the actual numbers on the 05, but my 06 just hit 60100 and over the past month ive noticed the mpg drop from about 18 to 20 on the highway and 15 in town to 13 on highway and 12 in town. any ideas to why this is? or any solutions to it?

 

Clean the MAF especially if you are running an air filter that requires oil. 60k sounds about right for a much needed bath for the MAF.
Use the search and it should turn up a DIY for cleaning.

Post up the results.

 

the cai has been on for only 1k or so and the maf was cleaned during install.

 

Might be time to bite the bullet and change the spark plugs.

 

Might as well disconnect the battery for a few minutes to reset the PCM...

 

yeah i wasnt sure ppl were making it on plugs and fuel filter. i know a lot of people wait the 100k but i didnt know if they could notice any difference.

and i have a gryphon so the pcm has been reset recently on my last update of tunes

 

thomabro

You might want to check out your locking hubs, they might be sticking or gone bad if you have 4 wheel drive.
Today I found my left front locking hub (actuator) was bad would not disengage, my front axle was turnig all the time, that will hurt your gas milage......

 

I definitely noticed a difference when I changed plugs at about 75K...

 

nope its a 2wd, thats a good idea though i never would have thought of that if it had been 4wd, and thanks minus.... unfortunately it will have to wait till i get my student loans in aug.

 

Plugs will cost you $65 to $75. It will take you the better part of a day to do, though.

 

If you change them yourself, do some research here so you know what you are getting into. Some will likely stick and break.

 

Might also want to look at those upstream O2 sensors. When they start to go bad, you can lose fuel mileage. And no, they do not throw a code when they gradually go bad, only when they completely fail. I know changing them on my 2003 at 65000 miles improved fuel mileage from 13 to 15-16 in city driving.

Just a thought.

 

how can i tell if they go bad? i cleaned them and what not when i took them out for the LT header install

 

Fuel mileage deteriorates, especially in closed loop situations (part throttle cruise at speed and warmed up). The only way I know to test them is to replace them, unfortunately. I have heard that they can be tested using a scan tool that reads the feedback generated from the O2 sensors, but those testers usually are dealer only, or run in the $10,000 range for independent shops. I have usually just changed the upstream sensors at 60,000 to 75,000 miles, or whenever I mess with the exhaust system, whichever comes first (the 'in the neighborhood' excuse).

 

Don't think you are supposed to "clean" the o2's. That might be the problem, IDK.