Bought a '04 F-150 Lariat crew cab 4x4 5.4L with 223,000. The only 2 Mods are a cold air intake and single inlet/ dual outlet flowmaster. I get about 12.9 city and only about 12.6 Hwy caculating it myself at fill ups. The message center says 12.8 all the time. I know 13 is about right for the city, but whats wrong with the Hwy mileage.

2 things wrong: P0420 code and a slight skip in overdrive under load running mid-grade.

So what can I do to correct these without buying new cats and why do you think my hwy mileage is so bad. Thanks in advance!!

 

Anytime you have an active code for exhaust/o2, your mileage is going to go down the tube. Either get your cat replaced or cleaned (or gutted ).

I have a 5.4 with 192k on it Fx4 supercrew. I can get to a max of 15 or so mpg with my cold air, single in/dual out flowmaster and SCT tune.

 

How would you suggest cleaning them? If I gutted them, that would throw a code too, right? Been hearing about spark plug foulers. Have you ever used them? What is an SCT tune?

 

Here's a pretty good video on cleaning them. He's very enthusiastic, but good.

***VIDEO REMOVED AS I CAN NOT VOUCH FOR THE PROCESS***

I've never used a spark plug fouler, maybe somebody can chime in on that for ya.

SCT is the brand of tuner that I use on my truck to reprogram the computer for performance, etc. I had a custom tune made.

Gutting them could lead to codes. I generally don't recommend it unless you want to invest in O2 simulators

 

Did that dude just tel me to pour lacquer thinner into my gas tank?


Some how, I find that to be ill advised. But I cant say as to why...

Better not spill any on the paint in the process...

 

Very Interesting! Has anyone on here personally tried the laquer thinner in their tanks?

Also, Do you think the Cold Air Intake could be changing the fuel mixture and causing the P0420 code?

 

Apparently it eats up all the gunk and whatnot pretty nicely. Also, it shouldn't be very dangerous if you don't put it back in sopping wet in thinner. I've never done it, but it doesn't seem too bad if done correctly. I had the same "WTF" moment at first.

As far as your CAI, I don't think that would be the cause. I drove mine for a good six months before I got my tune done.