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What's Causing a Strong Gas Smell near Exhaust

This is a discussion on What's Causing a Strong Gas Smell near Exhaust within the Technical / Maintenance forums, part of the General Discussion category; Howdy, When I startup my '03 GMC Sierra, 5.3L, Z71 4x4, there's a strong smell of Gas around the exhause ...

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    Question What's Causing a Strong Gas Smell near Exhaust


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    Howdy,

    When I startup my '03 GMC Sierra, 5.3L, Z71 4x4, there's a strong smell of Gas around the exhause pipe.

    It has 72,000 on the original tune & plugs and runs quite well.

    Anyone know what's causing it...?

  2. #2
    Get in sit down hang on. SolMan98's Avatar
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    Re: What's Causing a Strong Gas Smell near Exhaust

    Sounds like it's running rich. Bad O2 can cause that.

    Or do you mean you actually smell gas without it running? That sounds like a leak.
    Last edited by SolMan98; 02-23-2006 at 08:17 AM.

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    Re: What's Causing a Strong Gas Smell near Exhaust

    There is alway a small amount of unburned fuel during startup. Truck may be running well but not perfectly. It is likely that with 72K miles there is something that is no longer functioning at it's designed efficiency.

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    Re: What's Causing a Strong Gas Smell near Exhaust

    Quote Originally Posted by 1996Silverado
    Sounds like it's running rich. Bad O2 can cause that.

    Or do you mean you actually smell gas without it running? That sounds like a leak.

    i've had alot of people tell me it smells like mine is running rich, i have never smelled anything, i hope to god its not an o2 sensor, cause i got like 6 or 7 of them. although i have got o2 sensor codes before, but they were always acompianed by running lean codes, and low cataylst codes and an awful working truck, only happened a couple times since i gutted the cat.
    2003 Chev Silverado 4x4 4.10 gears and it has a 4.8L
    1997 GMC Sierra 4x4 4.3L 4L60E KOSS CD player,16mpg,3.73 gears z71 skid plates <<<sold

    4th year apprentice at Chev Dealer

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    Get in sit down hang on. SolMan98's Avatar
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    Re: What's Causing a Strong Gas Smell near Exhaust

    Quote Originally Posted by kenman1717
    i've had alot of people tell me it smells like mine is running rich, i have never smelled anything, i hope to god its not an o2 sensor, cause i got like 6 or 7 of them. although i have got o2 sensor codes before, but they were always acompianed by running lean codes, and low cataylst codes and an awful working truck, only happened a couple times since i gutted the cat.
    You should only have three I believe. My 5.7 has four.

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    1996 Silverado, 5.7, FIPKII, Elect Fans, S/S Headers, Duals, Wait4Me, 4/5 drop on 18" Weld Evo Velosity's. STOLEN ON 9/9/2006

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    Re: What's Causing a Strong Gas Smell near Exhaust

    Guys - It smells bad only while running. Must be real bad since my sense of smell is low.

    I do not get any codes. The temp is cold, about 15-20 degrees F nominally.

    Would you think the original spark plugs need changing - maybe they are not firing well enough and the gas is not burning efficiently...?

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    Get in sit down hang on. SolMan98's Avatar
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    Re: What's Causing a Strong Gas Smell near Exhaust

    Quote Originally Posted by tpitcher
    Guys - It smells bad only while running. Must be real bad since my sense of smell is low.

    I do not get any codes. The temp is cold, about 15-20 degrees F nominally.

    Would you think the original spark plugs need changing - maybe they are not firing well enough and the gas is not burning efficiently...?
    Plugs could probably use a changing. But if it running fine, then I think you problem is elsewhere. You could always pull a plug ot two and take a look at them. When mine was at about 95K-100K I noticed mine had a strong "rich" odor when I back my boat in the garage. Swapped the O2's and it went away. I was getting the occasional check engine light, but maybe 3% of the time it was on. Since I swapped the sensors, never had a light either. It can be starting to go bad, but still within limits so not to throw a code.

    D/D-2006 HHR 1LT 5-Speed.
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    Re: What's Causing a Strong Gas Smell near Exhaust

    Quote Originally Posted by 1996Silverado
    You should only have three I believe. My 5.7 has four.
    i just counted, 5 pre cat, and 1 post cat.
    2003 Chev Silverado 4x4 4.10 gears and it has a 4.8L
    1997 GMC Sierra 4x4 4.3L 4L60E KOSS CD player,16mpg,3.73 gears z71 skid plates <<<sold

    4th year apprentice at Chev Dealer

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    Get in sit down hang on. SolMan98's Avatar
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    Re: What's Causing a Strong Gas Smell near Exhaust

    Quote Originally Posted by kenman1717
    i just counted, 5 pre cat, and 1 post cat.
    six O2's for a 97 4.3?

    D/D-2006 HHR 1LT 5-Speed.
    1996 Silverado, 5.7, FIPKII, Elect Fans, S/S Headers, Duals, Wait4Me, 4/5 drop on 18" Weld Evo Velosity's. STOLEN ON 9/9/2006

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    Re: What's Causing a Strong Gas Smell near Exhaust

    Quote Originally Posted by tpitcher
    Guys - It smells bad only while running. Must be real bad since my sense of smell is low.

    I do not get any codes. The temp is cold, about 15-20 degrees F nominally.

    Would you think the original spark plugs need changing - maybe they are not firing well enough and the gas is not burning efficiently...?

    I would say that it is probably normal for 15 degrees. The computer has to really richen up the fuel mixture for the cold engine to idle when the temperature is that low. Wait for some warmer days (40+) and see if you can smell anything then.

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    Re: What's Causing a Strong Gas Smell near Exhaust

    Quote Originally Posted by kenman1717
    i just counted, 5 pre cat, and 1 post cat.
    Should only be 4...3 pre-cat and 1 post-cat.



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    Re: What's Causing a Strong Gas Smell near Exhaust

    Quote Originally Posted by 1996Silverado
    six O2's for a 97 4.3?
    you now see why i don't want to replace any.
    2003 Chev Silverado 4x4 4.10 gears and it has a 4.8L
    1997 GMC Sierra 4x4 4.3L 4L60E KOSS CD player,16mpg,3.73 gears z71 skid plates <<<sold

    4th year apprentice at Chev Dealer

 

 

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