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Need insight on 99 gmc c2500 5.7L

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  • #1

    Need insight on 99 gmc c2500 5.7L

    Trucks great....in gas mode. So I'll go fill up on CNG and drive 20, 40 sometimes 60 miles then bam it will switch to gas like it would when I run out of nat gas. My check engine light comes on naturally and it comes up as my maf sensor. It has been doing this lately when I fill up with cng. When I turn off the vehicle and turn it back on it will run on cng fine with my check engine light on. If I reset the code it just does it again. Do I have some kind of underlying problem with my cng kit which is an impco kit or should I just spend the $300 and get a new maf sensor? The light never comes on in regular gas mode just when I am running on cng. Any ideas other than the obvious? I've cleaned the sensor with electronic cleaner and replaced my air filter with new and it is still unchanged.

    Thanks!
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  • #2
    Re: Need insight on 99 gmc c2500 5.7L

    What is the code you are resetting?

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    • #3
      Re: Need insight on 99 gmc c2500 5.7L

      Sorry if I didn't make myself clear with the check engine light and my maf sensor. Its po1o1

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      • #4
        Re: Need insight on 99 gmc c2500 5.7L

        Have a close look at the wires going into the maf sensor connector. I have seen several that have had the wires broken inside the insulation right up next to the connector. You can lightly tug on each individual wire. If the copper is broken inside the insulation it will pull apart and you will have found the problem.

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        • #5
          Re: Need insight on 99 gmc c2500 5.7L

          Originally posted by karlhafen View Post
          Have a close look at the wires going into the maf sensor connector. I have seen several that have had the wires broken inside the insulation right up next to the connector. You can lightly tug on each individual wire. If the copper is broken inside the insulation it will pull apart and you will have found the problem.
          But wouldn't this also occur in gasoline mode as well as cng mode? It does not happen in gasoline mode just cng.

          Thanks so far

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          • #6
            Re: Need insight on 99 gmc c2500 5.7L

            So I bit the bullet and replaced my mass air flow sensor last week and everything is fine again. Runs perfect in both modes. Thanks for the replies

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