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Discussion Starter · #1 · (Edited)
I just bought a 2004 f150 4.6 stx (new body style). I should be getting about 18mpg on the highway, maybe more with a tune up right? When I for checked the mpg I was getting 11.5. I don't usually drive with my foot in it, so I started running down different things to try and fix the problem.

-I cleaned the MAF sensor.
-I replaced the Air filter.
-I removed the throttle body and elbow and cleaned both spotless, and cleaned all the EGR ports. Some were pretty clogged
-I noticed the EGR valve was missing the cap and the vacuum port was clogged, so i replaced the EGR valve altogether. (I thought this would fix my problem)
-I cleaned the fuel injectors.
-I replaced spark plugs
-I replaced the fuel filter

After I finished, now its thowing an o2 sensor code P0053. It wasn't throwing a code at all yesterday. And I'm still only getting 14 mpg, which will drop back off after a few hundred miles.

Right this second I'm waiting for my truck to cool off then I'm going to check the fuses and wiring, if those are good I will replace that o2 sensor.

Any one got an idea about what else I need to try if the o2 sensor doesn't fix the mpg? I'm at a loss if replacing the o2 sensor doesn't work.

At the moment its not throwing any other codes?
Should I try... Coil packs?
Catalytic converter?
Replace injectors?
Replace maf sensor?
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