98 z-71 bad gas mileage

johndoe17d · 04-13-2009, 11:34 AM

I have a 98 z-71 Ext. cab i'm only getting about 9.5 to 10 miles per gallon. i have have on idea why but it seams to run fine.
If someone can help i would appreciate.

stumpuller454 · 04-13-2009, 12:41 PM

may need a tune up(Including compression test), if it already hasn`t, and probly check to see if the cats are plugging up, plus making sure your tires are set to proper pressure, should be good!

Erock80 · 04-13-2009, 12:47 PM

Lots of factors come into play when you consider fuel mileage... Tires, brake drag, tune-up, air filter, alignment, driving habits and distance are a few that come to mind.

I have basically the same truck, just without the Z71 option. But I drive her easy and keep my foot out of it, and on the open highway I've seen a hair over 20mpg. However, through town and in the stop and go of the burbs, I'll easily cut that right in half and it'll drop down to 10-12mpg.

There's lots you can do to improve your mileage, some are gimmicks and some are proven. Biggest, easiest and least expensive trick... keep yer foot out of it.

Look into how well your motor is running, your tires (are the under inflated, misaligned, aggressive tread), even bad shocks can eat up mileage. But if you're mostly driving it a short distance, with stop and go traffic, I hate to tell ya, but I don't think there's anything you can do. Except maybe, get a Geo.

Good luck

bradrhale · 04-13-2009, 02:14 PM

is this a recent thing or has it always gotten this mpg?? what size engine??

johndoe17d · 04-13-2009, 05:49 PM

Its got a 350 with 3.42 gears and its like its slowly gone down hill on mileage. I replaced the plugs, plug wires, and dist. cap and rotor not long ago. I'm not driving it hard i keep the the rpms under 2000. On the highway the best i got was about 12 mpg with the cruise set 65.
I have a 84 k20 long bed with 8 inchs of lift and 35 boggers 4.10s. I get 10-12 mpg in town with it.

passport · 04-13-2009, 05:56 PM

That truck should do better than that. How many miles do you have on it? How big are the tires? Is this a lifted up 200k mile truck?

johndoe17d · 04-13-2009, 06:02 PM

Its got 156000 miles no lift running almost a 33 inch tire.

bradrhale · 04-13-2009, 06:38 PM

i dont know how mechanically minded you are so i apologize if my questions sound kindergarten type. 33s are not stock for your truck. did you have the speedo adjusted when the new tires were installed?? are you getting a service engine light in the dash?? when was the last time you had a fuel filter change??
i owned a 00 silvy with the 5.3, 3.42 gears. i avg about 12 and 13 mpg too. what mileage did you start out with??

passport · 04-13-2009, 06:43 PM

Quote:

Originally Posted by johndoe17d

Its got 156000 miles no lift running almost a 33 inch tire.

Thats gonna cost ya some, but 9.5 to 10 still seems low, what gears again?

johndoe17d · 04-13-2009, 07:13 PM

no the speedo wasn't adjusted. no check engine light. I'm goto get it scaned at advance to see if it has any codes in case the bulb has been removed or is out. also to pick up a filter. I'm not sure what the mpg was before. my last tank of gas i only got 197 miles out of it.

04-13-2009, 11:34 AM	#1
johndoe17d Junior Member Join Date: Apr 2009 Posts: 6	98 z-71 bad gas mileage I have a 98 z-71 Ext. cab i'm only getting about 9.5 to 10 miles per gallon. i have have on idea why but it seams to run fine. If someone can help i would appreciate.

04-13-2009, 12:41 PM	#2
stumpuller454 Senior Member Join Date: Dec 2007 Location: Grande Prairie, AB Posts: 2,206	may need a tune up(Including compression test), if it already hasn`t, and probly check to see if the cats are plugging up, plus making sure your tires are set to proper pressure, should be good! __________________ SUPERCHARGED 454 K2500 GMC! Watch My Youtube Videos!!<<<

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04-13-2009, 12:47 PM	#3
Erock80 Senior Member Join Date: Oct 2008 Location: Rochester NY Posts: 166	Lots of factors come into play when you consider fuel mileage... Tires, brake drag, tune-up, air filter, alignment, driving habits and distance are a few that come to mind. I have basically the same truck, just without the Z71 option. But I drive her easy and keep my foot out of it, and on the open highway I've seen a hair over 20mpg. However, through town and in the stop and go of the burbs, I'll easily cut that right in half and it'll drop down to 10-12mpg. There's lots you can do to improve your mileage, some are gimmicks and some are proven. Biggest, easiest and least expensive trick... keep yer foot out of it. Look into how well your motor is running, your tires (are the under inflated, misaligned, aggressive tread), even bad shocks can eat up mileage. But if you're mostly driving it a short distance, with stop and go traffic, I hate to tell ya, but I don't think there's anything you can do. Except maybe, get a Geo. Good luck

04-13-2009, 02:14 PM	#4
bradrhale Senior Moderator Join Date: Apr 2006 Location: Texas Posts: 9,512	is this a recent thing or has it always gotten this mpg?? what size engine??

04-13-2009, 05:49 PM	#5
johndoe17d Junior Member Join Date: Apr 2009 Posts: 6	Its got a 350 with 3.42 gears and its like its slowly gone down hill on mileage. I replaced the plugs, plug wires, and dist. cap and rotor not long ago. I'm not driving it hard i keep the the rpms under 2000. On the highway the best i got was about 12 mpg with the cruise set 65. I have a 84 k20 long bed with 8 inchs of lift and 35 boggers 4.10s. I get 10-12 mpg in town with it.

04-13-2009, 05:56 PM	#6
passport Senior Member Join Date: Mar 2009 Posts: 62	That truck should do better than that. How many miles do you have on it? How big are the tires? Is this a lifted up 200k mile truck?

04-13-2009, 06:02 PM	#7
johndoe17d Junior Member Join Date: Apr 2009 Posts: 6	Its got 156000 miles no lift running almost a 33 inch tire.

04-13-2009, 06:38 PM	#8
bradrhale Senior Moderator Join Date: Apr 2006 Location: Texas Posts: 9,512	i dont know how mechanically minded you are so i apologize if my questions sound kindergarten type. 33s are not stock for your truck. did you have the speedo adjusted when the new tires were installed?? are you getting a service engine light in the dash?? when was the last time you had a fuel filter change?? i owned a 00 silvy with the 5.3, 3.42 gears. i avg about 12 and 13 mpg too. what mileage did you start out with??

04-13-2009, 07:13 PM	#10
johndoe17d Junior Member Join Date: Apr 2009 Posts: 6	no the speedo wasn't adjusted. no check engine light. I'm goto get it scaned at advance to see if it has any codes in case the bulb has been removed or is out. also to pick up a filter. I'm not sure what the mpg was before. my last tank of gas i only got 197 miles out of it.