Question about 1993 Chevrolet K2500

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I pass every test for smog except for the emissions (HC) part. The limits are 120 at 15mph and 95 at 25 mph. I'm at 155 and 160. I've replaced the catalytic converter, entire exhaust from tail pipe to manifold, oxygen sensor, MAP sensor, throttle body gaskets, fuel filter, air filter, changed the oil and put in 20/50 weight oil, used sea foam to clean out fuel system and still not passing. I've also replaced spark plugs, spark plug wires, distributor cap and rotor as well.

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  • incognito619 Feb 09, 2010

    Yes I do have a TBI. The year is a 1992 chevy pick-up and I have a 350 small block. 5.7 liter k2500.

  • incognito619 Feb 09, 2010

    How do I adjust the fuel air mixture?

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Has anyone tried adjusting the fuel air mixture?

Based on what I am reading this is a gas engine and I am also assuming it is fuel injected. (Or does it have throttle body fuel injection?)

I suspect a case of dirty fuel injectors at the moment. They will need to be removed and cleaned.

If you have throttle body fuel injection then you will need the fuel air mixture adjusted.

If you respond can you let us know the "engine size" that is installed please. It would help us to help you in troubleshooting.

Thanks for using Fixya. Kelly.

Posted on Feb 08, 2010

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  • Kelly
    Kelly Feb 10, 2010

    Hi again,



    After digging into the books your fuel air mixture is controlled by the ram air damper door position sensor. The sensor should be near your air filter outlet. You might be able to cheat the position of the sensor by losening then screws and turning it clockwise and re-tightening the screws. The sensor regulates the fuel air mixture at 14.7:1 by controlling the amount of fuel introduced into the throttle body by the throttle body injectors. If you can't tweak the position of the sensor then your probably going to have to replace it.



    BEFORE replacing the sensor I would MAKE sure there were no vacuum leaks on the engine.



    I can NOT tell you to do this but... some of us have been known to take an UNLIT but partially on hand held propane torch and sweep it across the intake and vacuum lines listening for an increase in engine RPM. (away from the air filter inlet) Increased RPM = vacuum leak



    Kelly

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Change spark plugs,wires,cap and rotor if they are over 24,000 miles
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Make the smog check appointment for the EARLY MORNING. Colder air will help the fuel burn better.

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Clean or change the air filter and pcv valve.

Clean Mass Air Flow sensor with CRC Mass Air flow cleaner or electronic part cleaner.

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Do a quick wipe down on the wires and cap to take the moisture off.

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Check spark plug wire contacts for corrosion.

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Fill the tank to around 3/4.......just in case your fuel pump is weak.

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Do not carry excessive cargo on the truck bed.


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Please post more information on the comment window.

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