p0442 and bad gas mileage

[joshwho44]

Hey, my name is Josh and I'm new to the forum although I have been reading around on here for a while. I'm in college and I've been driving a light blue '97 Explorer Sport SOHC for the past year now. It currently has 31x10.5x15s on black Pro Comp 15x8s. It also has a cone air filter and dynomax turbo muffler with 2.5" piping that exits behind the axle. I'll post some pictures in the next couple of days...

It has been a good vehicle with the exception of the transfer case going out last summer, but now I have a new problem. My dad had it for a few weeks in October and when I got it back from him I noticed the CEL was on. I got autozone to pull the code and it was a p0442.

This has been problematic because my gas mileage has plummeted and I need to pass emissions as my tag is expired now. My mileage has dropped from 18-20 to 15-16 on the highway and from 15 to 10 in the city. I've replaced the gas cap and some leaking vacuum lines with no result. I've also cleaned a sticking IAC valve and repaired a disconnected manifold tuning valve also with no luck...

At this point I really need to fix this problem while I'm home from college but I'm reluctant to take it to a shop and pay a fortune to have it smoke tested as I don't want to borrow any more money from my dad. Any advice?

 

[Cobraguy]

This is probably a leak in the fuel tank fill tube. But it can also be in a multitude of other places. This can be easy and cheap, or expensive. It just depends. Personally, if you don't have the time or resources to search this out, I would pay to have it located...even if you do have to go to Dad. If you have a shop that you can work in, drop the tank, etc, then you can look for the leak yourself. Keep in mind, some of these leaks can be VERY small.

After it's fixed, you will need to complete a drive cycle to pass emissions. That can sometimes be forced, but usually can take up to three weeks to complete.

 

[joshwho44]

Would the p0442 really be responsible for the large drop in gas mileage? I can get it smoke tested for $100 which I may do later this week.

The larger tires wouldn't be the cause of the gas mileage would they? It has 4.10 gears and the p255/65/16s that used to be on the truck aren't much smaller than 31s.

 

[Cobraguy]

Tires can cause a loss of mileage two ways. One, you are actually traveling farther than your odometer says you are, so when you calculate your mileage, you are using an incorrect (lower) mileage figure. (assuming you have not corrected the speedo) and two, you have changed the way the car is programmed to be driven. The shift points and torque curves are all different than factory. If I were to change tires/gears, I would have a tune done to correct for all the changes.