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crown vic failed, NOx emission

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  • crown vic failed, NOx emission

    Failed colorado enchanced emmission test, tested 2.68 GPM, spec 1.5. No SES light, never delt with this before, all the cng veh I have e-tested have passed even some real high mileage F150's. Always wondered if 8 new coil packs would wake one of these crown vics up, I sippose this might be the one to try it on, however it does not seem to have a dead cyl at lease at idle.

  • #2
    Re: crown vic failed, NOx emission

    you can have a bad O2 sensor without a Check engine light. you need to take a look at the long/short term fuel trims on a graphing scan tool and see it they are running to the rich side...

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    • #3
      Re: crown vic failed, NOx emission

      What year is the Crown Vic? Is this a factory CNG or a retrofit? High NOx is an indicator of a high combustion chamber temperature. EGR, carbon, high compression are some of the areas to look at when NOx is too high. Throw me some info and I'll look for bulletins.

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      • #4
        Re: crown vic failed, NOx emission

        High NOx is usually an indication of a disconnected EGR valve or a lean fuel mixture. A misfire due to a bad coil will result in low NOx but high HC. A rich mixture will show low NOx but high HC and CO.

        I would look for vacuum leaks first, then check fuel trim numbers for positive values.

        Franz

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