First off its a 99 ECSB Z71 5.3, only mods are a cat-back exhaust. I've been noticing i'm only getting about 11mpg in this thing and thats driving fairly conservetively. Is this normal? Recently I replaced plugs, fuel filter, air filter- the regular tune up stuff and didn't seem to notice much of a difference. So what I'm wondering is if it has to do with being a cheap *** recently and only runnin 87-89 Octane gas and possibly having a boat load of KR. Any ideas? At first I thought it might have been a 4wd issue, but then found out that all the autotrac front driveshafts rotate in 2wd mode-the thing that lead me to believe that could be an issue was the fact that it seemed like the front steering was stiffer when parallel parking the beast.

Thanks
J

 

Add some electric fans, and a computer tune, and you will get some increase in milage.

 

Somethings definatly not right. My old 99' used to get 16-17mpg w/ 265's when I first got it.
Hell even the heavy Nitto 285's only dropped it down to 15.

 

I'm totally lost as to what it could be, especially since i've changed all the regular tune up crap, even did the tranny fluid & differential fluid. I'm going to have to run some better gas in it once and see what kind of mileage I get out of that.

 

You sure its not stuck in 4WD or Auto 4WD some how?

 

Yeah I get 350 miles to the tank or about 14 MPG and that running a 5.7, Lunati cam and 8 psi on the whipple. I would say you just need a good tune it sounds like its running way rich. Give allen a call 210-626-0278 he will get you a good tune on your truck. Hope you get it figured out!

lator

Yellow

 

How many miles?
Maybe some new O2 sensors?

 

I'm sure its not stuck in 4wd, i've test that theory and roasted the rear tires-which im sure didnt help the gas mileage.

The only other thing I can think of is maybe its time to replace the two up-stream O2 sensors there are 74k on the originals.

 

Have you checked your fuel pressure. Could be your fuel pressure regulator has gone bad causing you to run too rich.

 

Haven't checked the FPR, is there a schrader valve on our trucks? I haven't ever noticed one, but can't say i've looked & now its a bit to dark out-but i have a fuel pressure guage sitting here.