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Oxygen issue

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  • Oxygen issue

    Got a call from a fellow with a 2015 2500 HD bi-fuel pickup.
    He's had the truck into the chevy shop several times as I gather.
    He gets an error code for too much O2 but only when he time fills at home. Doesn't seem to be an issue with public fueling. Public fueling is 15 miles up the road or 35 miles down the road. He does have a gas dryer inline ahead of the compressor. (van air cartridge) He is in a small rural type of community.

    I suggested that he contact the utility company as there is no way oxygen can be introduced through the compressor (Fuel Maker Q2 3600 psi)

    The question I have is - Anyone had issues with GM and excess O2 codes or have knowledge of getting O2 introduced in the utility gas line???
    The utilities up here relax the quality of gas in the summer and improve the quality during the winter because of our bone chilling temps.


  • #2
    That is an interesting situation. I'm with you that the culprit has got to be gas quality at his home vs. what is provided at the public station. Suggest you contact the gas utility and ask for a recent gas quality report at both locations. All utilities are required to publish these and here is, for example, what Dominion Energy publishes daily for Utah:

    This page may be helpful in reading the reports:

    If you can post the actual OBD error code that the truck is setting it could also help us figure out what is going on. My sense is the code is showing O2 Rich. Which indicates a rich fuel mixture at the house due to a low methane count (under 90%) with high ethane, propane, butane, etc.


    • #3
      P0171 and po174 code. Lean bank 1 and 2. (relayed information from the owner - I'm not an auto mechanic)


      • #4
        Running lean means not enough hydrocarbons in the air/fuel mixture...
        So I'm betting that you will find the gas report for his area will show high nitrogen levels, low methane. Running lean usually causes high catalyst temperatures, and premature cat failure.


        • #5
          I don't know if they still do it but the old propane peaker plants really screwed up pipeline gas in some areas. When there was a natural gas curtailment in an area served by a utility, some had stored propane that would be mixed with air and put into the natural gas distribution system. With the vast amounts of true natural (methane) gas we now have, I can't imagine any of these plants still existing.


          • #6

            same truck, same year, exact same issue, replaced MAF 3-4 times, each time solved the issue for about a year, lifetime replacement from Autozone. If it doesn't cure the issue he can take it back and get a refund, The CNG injectors have a much harder time compensating for various engine demands and atmospheric conditions, anytime the variance is off (however slight), the computer "protects" the engine by shutting down CNG and goes back to gasoline. He will need to disconnect the neg. battery cable for a few min to clear the codes and or a code reader to do the clear.

            Spoke to a service manager @ Chevy and was told this information after a few trips to the dealer. MAF gets a little bit contaminated its not a big deal when on gasoline, the gasoline fuel injectors can easily compensate especially in the L96 engine as they have oversized injectors, on CNG it can not compensate so it throws a code and reverts back to gasoline, fresh (new) MAF cures the issue, I never tried the MAF spray cleaner but it may work, since i have lifetime MAF replacement i dont mind doing this once a year, its a 5-10 min job max.

            Most recently I increased the fuel pressure on the GFI regulator, we will see if that makes it easier for the CNG injectors to keep up, so far so good. Pressure regulator increase is a bit tricky, if he doesn't know what he is doing he can really screw things up. he should be running a GFI P214-990 regulator. It is located between the driver side rear passenger seat and the rear driver side tire under the truck behind a steel plate secured by 2 bolts, if he takes the shield off he can verify the regulator part number.

            There may be a gas supply issue but this is a free fix to test that takes 10 minutes. Ive thrown the code both on road trips and when I home fuel, my compressor inlet pressure is 5 PSI with a AC630 supply meter, I've filled dozens of vehicles from home all but my Chevy were dedicated CNG vehicles and thus didn't have the option to switch back to gasoline. I was halfway across the country and stumbled into a large Chevy dealership with vast amounts of experience with these bi-fuels and thats when the service manager told me what was going on.
            Last edited by trdscfjc; 09-05-2018, 08:30 AM.