I KNOW I KNOW I'm sure this has been talked about to death about the bad gas mileage that we have. I just finished my heater core replacement man that sucked...but I was just thinking I'm getting 9-10MPG in the city and 11.5 on the HWY I've been racking my brain to try and figure out what could be the problem because I hear about people getting 15 on the hwy. Is there anyway I have a bad o2 sensor without it triggering a CEL? Thanks for any help.

 

When was the last time you did a tune up: such as plugs, cap/rotor, wires.

 

Here is one way to figure out if your O2 sensor (Or any part on your vehicle) is bad/worn:

"When is the last time you changed it?"

"I dont know."

 

well for one you have 4.10 gears, and it is my understanding that running at 70mph on the hwy, you will be turning around 2500rpms, but with 3.55s like i have at 70 im turning right at 2000rpms.

gears do make a difference.

 

My truck has 4.10's as it is an offroad package, and I have still gotten about 15 or 16 mpg on a roadtrip where most the drive was on the highway cruising around 70mph.

 

Plenum gasket may be blown

im currently getting 13-14 city, and around 17 highway... that is no joke. i also have take very well care of my truck, and im basically replacing everything with new parts. 65% of the parts on the truck have been replaced in the last 30K. i also ont hammer on it that much, and i hardly do any 4 wheeling.

and i have 4.10's and tach about 1900 at 70 mph

Takes time, effort, lots of new parts, and lots of money to get them going good, but its worth it.

 

thats weird cause i have 3.55s and have not done the plenum, and i got 15 hwy this past weekend.

all i have done is MSD SF 8mm plug wires, bosch copper plus plugs, and a k&n drop in. though i did my my 3815 on mileage xs.

and you both have to remember you have 360 with 4.10s he has a 318 with 4.10s

 

What size tires do you have.
Cause that kinda affects you're odometer.
(I see you got skyjackers so I assume you don't have stock tires)

 

Well I did a tune up less than 6K ago, cat back exhaust, brand new 265/70/17 tires I did go down a size from 275 but that's just width. I've never changed the O2 sensor since I've only put 9K on the truck since I bought it almost 2 years ago. It has new brakes, rotors, I do know it needs new tie rods but other than that the truck is in great shape just bad gas mileage. I drive 1.2 miles to work each day but I do drive about 60 miles once every other week and once in a while a road trip. But the gas just sucks. The plenum gasket is ok I believe I looked down the TB and did not see any oil.

 

yes it is possible for an O2 to be bad and not trigger a CEL right away, mine went bad along with my cat and never knew till it was replaced, my mpg went up 2mpg!!!