gas mileage is still down

2008 GMC SIERRA
108,000 MILES
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GYAKUBIK
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  • 3 POSTS
I have changed the spark plugs and cleaned the throttle body. the gas mileage is still down about 3 miles per gallon. Should I change the oxygen sensors and why. It has a 5.3 L in it
Feb 24, 2012 at 5:54 PM
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CJ MEDEVAC
  • ✓Experienced Mechanic
  • 11,000 POSTS
IS YOUR CHECK ENGINE LIGHT ON?

THE MEDIC
Feb 24, 2012 at 6:38 PM
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CJ MEDEVAC
  • ✓Experienced Mechanic
  • 11,000 POSTS
DOES YOUR RIG SHOW ANY OTHER ABNORMAL SYMPTOMS?

THE MEDIC
Feb 24, 2012 at 6:40 PM
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GYAKUBIK
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No, The truck is running fine. It's just gas mileage is down. I also keep tire pressure up to about 40 - 42
Feb 24, 2012 at 7:09 PM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,248 POSTS
Not related to the MPG, but with air pressure that high, you are going to wear the centers out of the tires.

As far as the MPG, make sure the air filter is clean, there are no vacuum leaks...
Feb 24, 2012 at 7:16 PM
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GYAKUBIK
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  • 3 POSTS
KN filter and has also been cleaned. not sure on checking for vacuum leaks. how can I tell if there is a leak
Feb 24, 2012 at 7:40 PM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,248 POSTS
For directions, go to our homepage under the DIY section.
Feb 24, 2012 at 8:14 PM
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