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CNG stopped working

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  • CNG stopped working

    I have a 1999 Cavalier, and over the last month the CNG started to slowly die.
    Sometimes it would start on CNG other times it wouldn't. Usually on a full tank I would get 180 - 220 km but now if it starts I might get 20-60km before it changes to regular gas.
    I am assuming it is either the regulator or CNG filter.
    Any ideas out there.

  • #2
    Re: CNG stopped working

    first check the 20 amp fuse in the fuse box under the hood on the drivers side fender. The turn the ignition on and listen for the tank valve to open, flip down your rear seat if you have to to listen for it/ It should sound like a "tink" you would have hear this while it was working. No tink means bad tank valve or no power to the valve. If you smell a natural gas leak in the front of the car your low pressure regulator is shot (very common), if you smell it coming from the left rear of the car, your high pressure reg is shot (very uncommon and expensive). If it's none of these it's your gas mass sensor (that box next to the low pressure reg)


    2003 Hummer H2 bi-fuel
    2000 GMC Yukon XL bi-fuel
    1999 International 4700 dual-fuel
    2007 Chevy Avalanche bi-fuel

    FMQ2-36 Fuelmaker w/ 24 GGE cascade


    • #3
      Re: CNG stopped working

      Thanks Murf,
      20 amp fuse is Ok, and I can hear the tank valve open each time.
      I don't smell any gas, so I am going to assume it is the gas mass sensor.


      • #4
        Re: CNG stopped working

        I'm wondering if you corrected this problem. I have a similar problem with my 2002 cav. The car only runs on CNG when it's cold, first thing in the morning. It will stay on CNG for ten or fifteen minutes then you feel a momentary power drop and it switches over to gasoline. It only starts on gasoline after that, until the next morning. Any Ideas?


        • #5
          Re: CNG stopped working

          I am having a similar problem with a 2001 cavalier. It only recently started, and isn't quite as severe as what you have described, but lately if I am anywhere below the 1/4 tank mark, my CNG will start alright, but just as you described, it will suddenly lose power and switch to gasoline once the engine warms up. I know it isn't empty because when I refuel, I will only get about 4 gallons. It definitely seems temperature related though, because on very cold days, I can get all the way to work (about 8 miles) without a problem, but if it is warmer in the afternoon, or a warm morning, I can never make it 8 miles if my gauge is at or below the 1/4 mark. It also tends to only be a problem when I am driving in town... stop and go. If I am on a steady stretch of freeway, I will always get down to the "check gauges" light before I switch over. In fact, the loss of power and switch to gasoline almost always occurs when I am accelerating after a light. Anybody else notice these types of issues?



          • #6
            Re: CNG stopped working

            I took my car into the shop yesterday and they said they diagnosed the problem as a bad low pressure valve. I have to wait several days for them to receive the parts. The repair will cost $400-$500 dollars. I'll let you know if this fixes it. Additionally my check engine light was coming on in weeks prior to this and it has finally come on steady. Chevy said this is associated to the problem.