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2002 Cav switches to gas at 1/4 tank CNG

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  • 2002 Cav switches to gas at 1/4 tank CNG

    Anyone have a recommendation on this? The car switches to gasoline consistently at 1/4 tank CNG. There are no other symptoms. I think, from reading another thread, it might be the pressure transducer...?

  • #2
    Re: 2002 Cav switches to gas at 1/4 tank CNG

    Might be. Do you fill at public fueling stations and if so how much fuel will the tank hold? When empty the tank should take at least 5 gge of fuel. Depending on conditions you should be able to travel between 120 and 140 miles on a tank. A tank that switches at 1/4 full will take around 4 gallons and around 100 miles of range (more or less). If this is the way your car is acting, it's most likely a pressure transducer. If you are getting the fill and/or range numbers I stated above, it's something else. The transducers are not cheap and there is a work around if the unit is bad and you don't mind having a non-operational fuel gauge on CNG. The transducer has a 5 volt reference voltage applied to it and there is a chart that shows voltage vs pressure I will try to dig up. That way you could verify if it is the transducer or something else like the tank temperature sensor. Fuel level is a combination of pressure and temperature---the pressure transducer actually causes the changeover to CNG at around 200 psi, but if the terperature sensor is faulty, the fuel gauge would be inaccurate. Keep in mind, unlike a Honda, the fuel gauge in a Cavalier is not very linear. A quarter tank on the gauge plunges like a rock and won't get you very far anyway .

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    • #3
      Re: 2002 Cav switches to gas at 1/4 tank CNG

      Thanks for the help. This car is only going around a hundred miles or so on CNG, so it might be the transducer. I will look at the CNG maintenance supplement and see what it takes to change the part, unless you have another suggestion.

      I actually have another cavalier (year 2000) with a cng guage that never reads full even when it's full, but I get the full tank (130 miles) usage from it, so I haven't bothered to attempt a repair on that car.

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