So there has to be something wrong with my truck. I know a lot of you guys are getting like 12mpg in town and up to 16 on highway. I am getting 8 in town and 12 on highway. I have a 2000 quad cab 5.9 auto 4x4. Tires are 285's so nothing big really. I have gutted cat, super 44 si/do, and mopar air cleaner. Nothing has made it better. It seems to run just fine, maybe a little high idle idk. It usually is 700 or so idk it moves around i think. No cel, so can it still be o2 sensor? Let me know what you think.

 

I think a few people have replaced the 02 sensor and got better gas mileage. I am going to replace mine this spring.

 

Can an o2 sensor be bad without a CEL??

 

Mine never has thrown one but when I replaced it I got alittle better mileage started to get 400 miles to the tank agian which averages out to arounf 12 mpg but I do alot of mixed driving and and like to go fast

 

You might be getting getting more than what you think. If your speedo hasn't been calibrated for your tire size.
go to this site.
http://www.miata.net/garage/tirecalc.html
stock tires are 245/75/16 (at least for my 98). Assuming you are running 285/75/16, you are off by 7.8% (slower). When your speedo reads 60, you are actually going 64.7.
That doesn't really measure up to much of a diff, roughly .6mpg, BUT it also changes your gearing and is more of a load on your motor to get up to speed.
I am running 265/75/16, its under the 3% variance, so i am close to real numbers.
but I would check all the typical RAM issues, CAT, O2 sensor, and plenum.

 

Its a Ram, they are great trucks don't get me wrong, but i don't think they put fuel mileage into play when being designed. My V10 in a dually i recently got the best ever and that was 13MPG and that was after i cleaned the injectors, dropped the tank and cleaned the tank and put a new sock assembly on it. But i also got the common bolt ons. I like to play with it. Dodge great trucks, great power, but bad fuel economy something most of us got used too.

 

If you are trying to run the stock O2 sensors
with a gutted catalytic converter
that is probably making your engine run very rich
or at least highly confusing your PCM computer.

Either go back to a high flow catalytic converter
so the oxygen sensors will get valid signals
or take out your stock PCM computer and install
an aftermarket PCM like the
MegaSquirt or FAST

 

It runs just the same when the cat wasn't gutted. My oil level hasn't change in a month so I don't the the plenum is that bad if it is at all. I know I won't get great gas milage but I know most are getting better than I get.

 

10 MPGempty or full, single or with a trailer. I'd be grateful for 12.