I know that our truck don't get very good mpg's but it seems the more parts i replace i get slighty worse mpg. I've replaced both O2's,IAC,MAP,PLUGS,WIRES,CAP/DISP,180 T-STAT and only get 11.3-11.5 city and a 160 mile highway trip doing 65 i was able to get 11.7 i been very lite footed also have a superchips 3865 on the milage xs setting and run a botttle of octane booster along with 93 octane gas. I've looked down my TB with a flash light and a little dentist mirrow and my plenum still looks okay.



01 1500 CC 5.9L auto 4x4 ORE 31's

 

Hhhmmm..... You should be able to do better than that. Quite a bit better on the freeway. What brand O2 sensors did you install?

 

Same thing i thought i've seen post with others reporting 12.5-14 city and 16-19 highway. Bothe are NTK

 

Well, that shouldn't be it then.....

Hows your cat?

I might be tempted to put the PCM back to stock, and see what mileage does.......

Is your truck an Off-Road edition? Do you have the 4.10 gears??

 

I replaced the pre cat O2 friday and it looked a little chalkie but okay. I have'nt pulled the 8th spark plug to see if its fouled i will tomorrow and report back. but the cat seems fine. I only got the tuner 5 days ago and had the truck for almost a year and it's been the same mpg but atleast with the tuner i can feel the HP and Torque. yes its the Off-Road edition with the 4.10 gearing.

 

So much for that thought.

Look at the rear plugs on the even side. See what they look like.

 

The higher the octane I run, the worse the mpg gets. Also, if it's getting cold there, it will take longer to warm up. I turn the heater to OFF until the t-stat is up to 180. After a drive, check the wheels to see how hot they are in case there's a sticking caliper or drum.

 

Pulled all the plugs (NGK) and all looked good and gapped to 40. Yes it's getting sorta cold here (georgia) but truck warms up within 15 mins of driving. I replace the front rotor's (drilled & slotted) and they are free the drums i had turned and there also free.

 

If your only engine modifications from stock are the ones you've listed, I have two thoughts:

1) Stop adding octane booster and stop using 93 octane gas. Gasoline is a mixture of hydrocarbons. The "octane rating" at the pump is not a measure of the octane in the gas; it is actually the Knock Resistance Index which is measured in units called "octanes" because octane is one of the hydrocarbons in gasoline and has high resistance to pre-ignition. High octane gas is not higher quality gas. It does not burn cleaner nor does it produce more energy, it is simply more resistant to preignition due to its higher flash point. It is more expensive due to additional fractionation procedures to yield a different mixture of hydrocarbons. Sports cars and race cars use high octane gas because their high compression engines (11:1 to 16:1) need gas that will not spontaneously ignite under the higher pressure before the spark plug fires.

Your engine has a 8.9:1 compression ratio and was designed to run on gas with a minimum octane rating of 87. Adding octane booster to 93 octane gas is giving you around 108 octane gas (could be more or less depending on brand) which is far, far outside of what your engine was designed to run on. Your "super gas" is killing your fuel economy because it doesn't burn well in your low compression engine. Your 180 degree thermostat lowers the temperature of the engine which adds to this effect.

The next time you fill up your tank, run it as close to empty as possible, then fill it up with 89 octane, don't add anything, and let us know how it goes.

2) You have the off road package so maybe you're running tires which are very large (heavier), very wide, or have very aggressive tread. All three of those things increase rolling resistance which will hurt fuel economy. What tires are you running?

 

Yeah im stock just the superchips manual said run 91 octane with almost every tune but 87 and mileage xs. okay i'll run it till emity and try 87. My tires are 265/70/17 and are not aggressive at all. I have the K&N air filter in the stock air hat and been thing about adding a K&N cold air intake style unit.