I recently picked up a 98 4x4 Super Cab with the 4.6. The reason I bought this truck over a 5.4 truck was for better gas mileage. The best mileage that I have gotten out of it is 13.0X the day I bought the truck. The truck has about 110k miles and seems very sluggish. To give you an example, I pulled an empty 16ft utility trailer and had the truck floored for roughly 30 miles and I never got over 75mph, and even with it floored in 3rd gear, it would drop down to around 60-65mph going up gradual hills. Please tell me that this isn't normal for this truck. I just changed the plugs and air & fuel filter. I also had a mechanic run some induction chamber cleaner through it. It didnt smoke at all after running the IC cleaner through, so I figured it was fairly clean. Like I said, the day I bought the truck, it got 13mpg, over the next couple months, it has slowly gotten worse and worse. I check the mileage everytime I get gas and it has consistantly gotten worse. BTW, I do pretty much all highway driving, with maybe 10 or so city miles on a full tank. What do I need to do? Oh, and thanks for the great website! I have been lurking for a while but this is my first post. Thanks in advance for your help.

 

Any CEL? i got gas mileage like that on m 4.6 when my front O2 sensors went bad. But i had a CEL. Hope i helped and keep us updated.

 

Nope, no codes at all. Thanks

 

I would suggest checking some basics first, engine compression. tire pressures/alignment, dragging brakes, restricted intake (in CT. we have a problem with field mice/they love setting up home in the air filter housing/I don't know about OK.), dirty air filter, intake leaks, restricted exhaust system (I have heard of catalytic converters disentegrating and causing restrictions)and as a long shot incorrect cam timing/ignition timing.
I hope this helps
Steve

 

I havent yet checked the compression. I keep my tires at 32psi and judging by the wear pattern and the way it drives, I dont think it is out of alignment. The truck has recieved new brakes on all four corners since I noticed the power/mileage problem and coasts fine when I let off of the gas, so I dont think it is a brake issue. There is no debris in the airbox, being as how I was just in there changing the filter, but I havent checked the inside of the intake tube, I guess it is worth a shot. I dont think there are any leaks between the maf and the tb since it idles great and pulls smooth. I have been contemplating gutting the cats, but I hate to lose any backpressure, plus they look like they would be a Mother Bear to get to. As far as the timing, I guess it is worth a shot, if I cant figure it out.

Wouldn't you think there would be a trouble code?

Thanks guys for your help. I think I am going to go ahead and pick up some o2's tomorrow. I will let you know how it goes.

 

with that many miles it wouldnt hurt to change O2 sensors. You should be able to get them for about 40-50 bucks with warranty. Good luck. Easy change also. Did you say the throttle body and plenum(egr ports, etc) were clean?. My truck runs like new after i cleaned mine about (about 2 hours). Keep us updated.

 

Definetely check the Throttle Body/EGR ports/IAC .
Lots of threads on it
Do a search for "Rough Idle Problem" under my screen name
Green_98 youll find all the tips and pictures youll need

youll need a few tools, 10 bucks worth of gaskets from FORD, and 4-5 cans of 'throttle body' cleaner, and a couple-three hours work

Keep us posted, we'll help ya out!!