Failed smog test - high CO
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HT4100 4.1, 4.5, 4.9 Discussion, Failed smog test - high CO in Cadillac Engine Technical Discussion; Need some help please. My 89 Allante w/4.5L won't pass emissions due to high CO. HC and NoX are fine. ...
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    jpetera@cableone.net's Avatar
    jpetera@cableone.net is offline Cadillac Owners Member
    Automobile(s): 1973 Eldo convertible, 89 Allante, 03 DTS
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    Failed smog test - high CO

    Need some help please. My 89 Allante w/4.5L won't pass emissions due to high CO. HC and NoX are fine. Diagnostics show numbers for both O2 sensors constantly fluctuate from low to high. Replaced the front one, no change. Getting 30 mpg on freeway. Tried nearly empty tank with quart of denatured alcohol with no change. Anybody know what a likely cause would be? Most posts refer to high HC emissions instead of CO, so I'm at a loss. Help!

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    noahsdad's Avatar
    noahsdad is offline Cadillac Owners Connoisseur
    Automobile(s): '87 SDV
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    Re: Failed smog test - high CO

    Quote Originally Posted by jpetera@cableone.net View Post
    Need some help please. My 89 Allante w/4.5L won't pass emissions due to high CO. HC and NoX are fine. Diagnostics show numbers for both O2 sensors constantly fluctuate from low to high. Replaced the front one, no change. Getting 30 mpg on freeway. Tried nearly empty tank with quart of denatured alcohol with no change. Anybody know what a likely cause would be? Most posts refer to high HC emissions instead of CO, so I'm at a loss. Help!

    When the engine is at normal temp the o2 sensor reading should fluctuate. It's in a closed loop operation then, giving the ECM data to adjust fuel mixture.

    Usually high CO and HC appear together, due to a rich condition. Are you getting a rich smell? Check for leaky injectors, fuel pressure, stuck or blocked PCV valve, plugged air cleaner element, or possibly the converter.

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