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2001 GMC Sierra 2500 Question: O2 Sensor and poor MPG's

 

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alsaaron, Gasoline, Brighton, MI, January 02, 2011, 21:59
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I have a 2001 GMC 1500 4.8l and I am getting 11-12 mpg's on the highway, could this be an 02 sensor? My air filter is new, plugs, wires, and fuel filter are also new.

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    DaveJHM January 02, 2011, 22:20
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    If you had an oxygen sensor causing that much of a fuel economy loss, your OBDII check engine light would come on based on a "lean" fuel trim issue.

    A good diagnostic test is in order to see what is going on with your truck. A solid fuel economy test should be done. Make sure there is nothing causing an issue aerodynamically.

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    alsaaron, January 03, 2011, 07:43
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    There is a check engine light on, I will shoot up to Autozone and have them check the code.

    Thanks Dave!

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    DaveJHM, January 03, 2011, 19:53
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    OK, yes, check the check engine light - and if you have P0171 and P0174 together, you have a vacuum leak, air intake leak or something like that...which will make the engine ask for more fuel.

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    alsaaron, January 03, 2011, 20:07
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    I checked the code today, it said engine cylinder misfire...

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    DaveJHM, January 03, 2011, 20:33
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    This too can consume more fuel, if fuel is unburned by a misfiring cylinder.

    Or, worse yet, you could have a fuel injector on the misfiring cylinder sticking open. Check your oil level - does it smell like fuel at all? Is it high at all?

    These are just thoughts. A good diagnosis is in order, otherwise it will be lots of guesswork. Good luck.

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    alsaaron, January 03, 2011, 21:29
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    Thanks Dave, I will have too look into it a bit deeper.

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