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Old March 11th, 2007, 09:16 PM   #1
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Default 97 chevy 5.7 L

Just bought this truck a bit a go . Runs great , mileage is way below what it should be . 8.6 mpg pulling the Grand . Iv owned Silverados like this before and they all did 11 to 13 mpg towing .

It had a code for o2 sensor when i bought it . wiped out the code to see if it came back on but it has not .

question , will a bad o2 sensor kill fuel mileage ?

Same 3:73 Gears as the other had , New tires 45 psi .

New air filter , plugs are good blah blah . What else may be killing its economy ?
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Old March 11th, 2007, 09:28 PM   #2
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yes a bad O2 sensor will kill fuel mileage. and about every other emission thing will kill fuel mileage. Sometimes a Fuel pump that is on the outs can cause it too. Lots of things can kill it

what does it get not towing?
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Old March 11th, 2007, 10:08 PM   #3
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yes a bad O2 sensor will kill fuel mileage. and about every other emission thing will kill fuel mileage. Sometimes a Fuel pump that is on the outs can cause it too. Lots of things can kill it

what does it get not towing?
I hae not checked it on a truck only run yet .
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Old March 11th, 2007, 10:18 PM   #4
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I know when my O2 went on the blazer, it dropped 3-4 MPG's.
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Old March 12th, 2007, 01:51 PM   #5
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Spoke to a local shop today about plugging it in . Said to change the fuel filter first . Said it is common for them to plug up and go lean then the pc will compensate and get bad economy .

Filter was indeed pretty plugged . Ill see where it goes from here .

Thanks for the ideas guys .
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Old March 12th, 2007, 01:52 PM   #6
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I know when my O2 went on the blazer, it dropped 3-4 MPG's.
Thats what i figure im off by , 3 to 4 miles to the gallon compared to the other identical silverados i have owned .
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Old March 12th, 2007, 06:30 PM   #7
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sounds like your on the right track. I would put it in the air and check everything. the idea is make sure you eliminate anything that could drag a brake or cause undue load. I have even seen busted engine mounts cock an engine and the load on the driveline was enough to drop a couple miles off. have you checked the parking brake and stuff yet?
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Old March 12th, 2007, 06:36 PM   #8
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sounds like your on the right track. I would put it in the air and check everything. the idea is make sure you eliminate anything that could drag a brake or cause undue load. I have even seen busted engine mounts cock an engine and the load on the driveline was enough to drop a couple miles off. have you checked the parking brake and stuff yet?
Ya it had new rear brakes just before i bought it . Took care of that issue as they had the self adjuster screwed up and it would over tighten the D side rear brake . That was an early find

being i just bought it iv been going over and under it often . Ill see where im at now . If its still low ill take it in for a scan .
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Old March 16th, 2007, 11:35 PM   #9
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Catalitic converter plugged up?
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Old March 17th, 2007, 05:11 PM   #10
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when i put the new muffler on my 94 gas milage when up but had blak smoke 2 mpg turns out i needed a fuel fiter and a new o2 sener
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Old March 18th, 2007, 10:19 AM   #11
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Ran 15.2 on a trip yesterday 60 and 70 mph run , most of it 60 on a 2 lane so its still down from what i think it should get . Fuel filter helped .

This truck should run 16.5 to 18 on that type of run i think .
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Old March 18th, 2007, 01:32 PM   #12
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This truck should run 16.5 to 18 on that type of run i think .
it should, maybe the higher mileage of the motor has something do with it?

At best I can only get 16.5mpg out of my '99 Suburban w/5.7L(112k) and 3.73 gears. I have 265/75/16 tires.
But the 'Burban is carrying about 800-1000lbs more body weight than your Pickup.

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Old March 18th, 2007, 02:06 PM   #13
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Do you know what your compression is?
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Old March 19th, 2007, 01:23 PM   #14
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Do you know what your compression is?

I have not put a gage on it but it starts and runs strong , no oil consumption . No reason to think the motor has any internal issues .
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