I have a 2002 F150 Fx4 with a 5.4L V8 and 3.73 rear end. I'm getting not so great mpg (last I calculated, about 9.5 mpg). So I'm just trying to narrow down any possibilities. Plugs were changed recently. One of the possibliites I thought was the O2 sensors. I hooked up my OBDII reader and noticed that both sensors on bank 2 are not flucutating very much at all. Bank 2 Sensor 1 and 2 are both consistently around 0.5 - 0.6V. The bank 1 sensors jump from 0.08 to 0.7V so they seem to be working ok.

So my questions are:

Are the bank 2 O2 sensors not working if the voltage isn't moving?

I've attached a video of the OBD II reader and a pic. Sorry the vid and pic are sideways.

 

I think I already found the answer to my own question....Is it correct that bank 2 sensors after AFTER the catalytic converter? If yes, then I presume a steady value would be normal...so, if I understand correctly, the O2 sensors are working ok.

I'll check the air filter and PCV soon...not sure what else I can do to improve the mpg to be better than 9!

I'm coasting to stops.
I'm driving the speed limit.
I'm accelerating from stops such that the RPM doesn't go over 2000.

 

Fuel Consumption depends on fuel level. When your fuel is below 85% more than 50% of your fuel is evaporating.

 

Tire size? If its stock clean the MAF and throttle body. How's idle? Smooth as butter? If not I'd change the coils. I did when I did the plugs and I get almost 14 city. I was getting 7 at best ( 3 or 4 original plugs with 248,000 miles on them. Changed all the coils with new motorcraft ones. Also run some injector cleaner in the gas and change the fuel filter.

 

tires are stock size (LT245/75R16) but not stock load range. OEM calls for load range D tires. The tires on it are Michelin LTX AT2 tires, which are load range E. After doing a bunch of reading, I realized I never checked the air pressure (doh!)...so I did that, and the pressures were low (35 -40psi!). That might change things with respect to fuel economy right there. Boy oh boy, is tire pressure a hot topic...loads of threads...hard to get a proper idea of what is the best pressure. Anyways, the door sticker says 50psi front and 60psi rear. 60psi for the rear is surprising for a D load range tire (max is 65psi). Anyways, I put the air in the tires last night at 50/60 for front/rear.

Idle is smooth. I bought the truck from a used dealer (not a dealership) and it had a misfire in cyl 4. The used dealer changed the coil on cyl 4 and claims to have changed the plugs, but I wasn't given anything to prove the plugs were indeed changed. So I may have to go ahead and change the plugs. Note: I didn't start calculating fuel economy until after the misfire condition was fixed.



Thanks for the MAF/Throttle body and fuel filter suggestions. I'll work on getting that done. Not looking forward to changing the fuel filter though..but you're right, I'm sure it needs to be done.

PS. after some more research, I believe because the truck has the upgraded payload package (7700), the mpg will be lower than base model. Hopefully, I can improve mileage by a couple mpg though...

 

if it's an FX4 it has 265/70/R17's. How many lugs are on each wheel? 5 or 7? The tire size sounds like a 7700.

 

It's an FX4, but no, it does not have 265/70/R17s (I thought that was weird too). It definitely has 245/75/R16s; 7 lugs. A pic of the door sticker (and the truck) is attached.

 

that's a 7700 with fx4 stickers you couldn't get both packages

 

Ahh! lol well then. I bought it used, so what do I know lol. Anyways, why the hell would someone put FX4 stickers on a truck if it isn't? What's the point lol.

 

to look cool I guess. Anyway no the 7700 package wouldn't effect mileage. Just adds more payload and even harder to find wheels for because only the 7700's and 8200's ( 04-14) have 7 lugs. Anyway the decals on the sides aren't stock just the tape stripe at the bottom on the 2 tone. But looks like you found a good one.