1997 5.7 only 9 mpg

[travis mattson]

I have a 1997 vortec thats getting 9 mpg in town mostly. I was getting 12 mpg. Thinking about doing a ignition tune up and maybe a blackbear tune to help with MPG.
373 gears
4l60e
285 75 r16
New fuel pump
New mpfi injectors
Rebuilt rear diff
Reman trans
New upstream O2s
Downstreams on the way

is there anything I should like certain plugs, tune, tire size etc or is 12mpg the best ill get.

 

[kennythewelder]

I have a 1997 vortec thats getting 9 mpg in town mostly. I was getting 12 mpg. Thinking about doing a ignition tune up and maybe a blackbear tune to help with MPG.
373 gears
4l60e
285 75 r16
New fuel pump
New mpfi injectors
Rebuilt rear diff
Reman trans
New upstream O2s
Downstreams on the way

is there anything I should like certain plugs, tune, tire size etc or is 12mpg the best ill get.

Well, that's about what *m getting in my 97. 373 gears, with 285-60-15 tires. IMO, it has a lot to do with the ethonal in the gas. Alcoholic burns at a different rate that gasoline, giving less MPGs.

 

[L31MaxExpress]

Has to do with a heavy foot. My heavy ass 97 van always got 12-13 mpg around town if I kept my foot out of it. Got closer to 14 before 10% ethanol hit. Even my Q-Jet fed 400 hp Vortec 350 G20 van would get 13 mpg in-town. 9 mpg is not good.

 

[Old Bear]

My 2000 K2500 with 5.7L and 4.10 gears averages 9.5 MPG around town and 9.5 MPG down the interstate. At least she is consistant

 

[kennythewelder]

Last fill up and the few before I was at about 9.8 MPGs. Yes I have a lead foot.

 

[wirlybird]

My '97 Tahoe 4X4 LT 2 door 5.7L consistently gets about 16-17MPG. Computer was tuned when it was new but other than that nothing else done. 322,000 miles currently.
I only run non ethanol 87.

 

[MIHELA]

My truck gets 14-15 mpg mixed with 87 ethanol blend. 9 seems pretty low for a Vortec.

 

[GMCTruck]

Sometimes a change in fuel mileage can be something simple like a fuel filter or air filter getting plugged up.

 

[Dariusz Salomon]

I have a 1997 vortec thats getting 9 mpg in town mostly. I was getting 12 mpg. Thinking about doing a ignition tune up and maybe a blackbear tune to help with MPG.
373 gears
4l60e
285 75 r16
New fuel pump
New mpfi injectors
Rebuilt rear diff
Reman trans
New upstream O2s
Downstreams on the way

is there anything I should like certain plugs, tune, tire size etc or is 12mpg the best ill get.

Wow man-that's way off -I got 99 tahoe z71 with 3.73,265/17 and I get about 11.2 on lpg(propane) mostly short,5 mile trips to work-and you usually use way more of this stuff. On gas I used to get around 13 city-14.7 highway. And that was on 285s. And I have all those extra seats,barn doors and a massive chunk of roof to play with too.

 

[spf1268]

My 1996 C1500 single cab long bed with the 5.0 Vortec and 3.42 rear gears got 20.5 MPG going from CA to AZ and 19.5 MPG coming back home last week. Around town it gets 16-17 MPG. All on 87 octane.
My old 1997 5.7 RCSB with 3.73's was about 2 MPG down from those numbers.

You have a very heavy foot or something is wrong...