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CNG part inop(tank full, while fuel guage LED on switch indicates lowest level)

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  • Techie
    replied
    Re: CNG part inop(tank full, while fuel guage LED on switch indicates lowest level)

    It sounds to me that you have a Factory System. 1999 did use a 'fumigation' type of CNG delivery, it worked well, it just did not get as good of a fuel economy.

    Here is how it works: (This is from a GM service manual)

    The alternative fuel engine control unit (AF ECU) controls the fuel system while the vehicle is operating on alternative fuel. The AF ECU receives signals from various engine sensors and determines the correct amount of fuel required by the engine. The fuel is stored in a cylindrical fuel tank. A full tank can contain fuel at 3600 psi (24,820 kPa). A high pressure lock-off (HPL) solenoid in the tank and a low pressure lock-off (LPL) solenoid in the fuel line prevent fuel flow. The AF ECU commands ONLY the HPL open for 1 second at every ignition ON for a CNG prime pulse. The CNG prime pulse is performed in order to charge the fuel line and also allows the fuel pressure sensor (FPS) to monitor the amount of fuel pressure in the tank. The AF ECU commands BOTH the HPL and the LPL open when engine RPM indicates the engine is cranking or running on CNG.

    This fuel delivery system utilizes three different pressure stages in order to lower the fuel pressure from tank pressure down to a delivery pressure which is slightly above atmospheric pressure.

    High Pressure (tank) Stage

    When the AF ECU commands the HPL open fuel begins to flow (at up to 3600 psi) through the high pressure regulator (HPR). The HPR reduces fuel pressure to between 115-220 psi. The outlet of the HPR is the intermediate pressure stage.

    Intermediate Pressure Stage

    With a pressure between 115-220 psi the fuel exiting the HPR flows through the intermediate fuel line to the low pressure lock-off (LPL) solenoid. The LPL is controlled by the AF ECU. Fuel flows out of the LPL through another portion of Intermediate fuel line and into the low pressure regulator (LPR). The inlet of the LPR is the Low Pressure Stage.

    Low Pressure Stage

    The low pressure regulator is a two stage regulator. The fuel enters the LPR at the intermediate stage pressure of 115-220 psi. The Primary stage of LPR operation reduces the fuel pressure down to between 2-4 psi. The fuel pressure is then again reduced in the Secondary stage of the LPR down to between 2-5 inches of water column. The fuel exits the LPR and flows through the low pressure hose and into the gas mass sensor/mixture control valve (GMS / MCV).


    I would check for any Powertrain DTC's that may be stored. If anything other than P1202 is stored, I'd troubleshoot those first.

    It sounds like you either have a restriction in a line (look for very cold or frozen spots) or your pressure sensor signal is incorrect. Check those BEFORE you throw a High Pressure Regulator at it. If you PM to me with an e-mail address, I could probably e-mail you a copy of diagnostic sheet. If you got access to AllData, it is better yet. Check at your local library, some have it, some do not.
    Last edited by Techie; 07-16-2008, 10:15 PM.

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  • krnorth
    replied
    Re: CNG part inop(tank full, while fuel guage LED on switch indicates lowest level)

    Wow...this post baffles the cruddles out of me....what the tarnation are you guys talking about? I can't understand it or I would try to be of some help.

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  • siai47
    replied
    Re: CNG part inop(tank full, while fuel guage LED on switch indicates lowest level)

    What year and model vehicle are we talking about here?

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  • CNG part inop(tank full, while fuel guage LED on switch indicates lowest level)

    The car is a 1999 Chey Cavalier 2.2L eng. Mounted on the firewall under the hood is a EFS 100 (electronic feedback system controller), which i assume is for the CNG System. The Gasoline/CNG Switch with the integrated fuel gauge display is a LRENZO brand (its mounted on the dash by the steering wheel).

    The car starts and runs great on gasoline, but the CNG system is not working. The pressure guage under the hood reads 3000psi, but the electronic light displaying the CNG fuel level thats on the Gas/CNG Switch is lit at its lowest level (indicating either no CNG or a very low level). Someone told me that its an aftermarket CNG System.

    The Gasoline/CNG Switch with the integrated fuel gauge display is a LRENZO brand. Under the hood it has a "ventury" type CNG feed system that is mounted over the throttle intake (I believe its called a mixer), and is fed the natural gas via a 2-3 foot long flexible hose type of line, from the Pressure Regulator Assembly.

    Anykind of charts, diagrams, discription of operation, and or suggestions/tips would be greatly appreciated.

    Thank You Very Much
    Last edited by cng; 07-14-2008, 11:14 AM. Reason: added info
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