TieRod

My 03' 8.1l is getting some really bad gas mileage. The 01' I had got 13+mpg. With a HIC it still got 12mpg. This 03' I have now is getting 9mpg.
I need to figure out what the hell is causing it to be so bad. Anyone have an idea where to start?

hirdlej

iTrader: (31)

What's the final drive ratio/tire height/ body style of the 01 vs the 03 you have now?

TieRod

Both trucks are ECSB 4x4 3.73 gears. Same tires and wheels on the 03' that was on 01'. The 03' is 500lbs lighter then the 01' was.
Sense I bought the 03' I've done pugs, wires, o2s, rocker arms, and tuning. It had a K/N CAI on it and flowmaster mufflers.
Tuning didn't help the fuel mileage at all but the truck does run great.

nightrunner

iTrader: (4)

how about the fuel filter? maybe clean the air filter

lady3bglover

iTrader: (3)

Do you have a performance tune on it?

ZZebes

iTrader: (10)

Won't make a diffence since most tunes are close in the cruising/driving sections

the "performance" tune has more to do with WOT performance

Envelope Man

Hey Man, I have had the same issue with my 00 Sierra in the past. You said you changed plugs. What are they? If the are not ACDelco Uridiums I strongly suggest swaping them out. What grade fuel do you use? I used to run BP mid grade 89 oct. When I switched to Shell "V Power" my mileage went up by almost half. Believe it or don't, it's the truth. I would try these things first, you mite be surprised. Padre

TieRod

First things I did when I bought the truck.

I'm ran NGK tr5 in both trucks and use the same gas stations.

MeanZ71

iTrader: (6)

I'd suggest changing mufflers since flowmaster is a chambered exhaust and a straight-thru muffler is less restrictive which could help a lot since your big block wants to breath. For example: Dynomax bullets or Magnaflow

fastnblu

iTrader: (2)

Start w/ 8.1L. What is HIC?

Seriously, now...did it have a stock tune? How radical is that now?

Are u running same ratio rockers?

Did the other have a tonneau or some huge difference that you're forgetting or not currently using?

I'd think the Cd on the 03 would be slippier. I also thought the '03 would be heavier. Beyond that, I don't know.