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"Clicking noise" near tank

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  • "Clicking noise" near tank

    Sorry about being 'techno-phobic and just as inept. This is a great site. Wow! You all are on top of things.

    I have a 2002 Cav that had a new HPR, GMS, and computer (in bumper?) replaced right before I got it. It has run fine for about 5 months now, but the other day it died at a stoplight and has slowly started stalling worse until it only runs a few hundred yards on CNG, stutters, stalls, and dies. It starts right up for another hundred yards, then stutters and dies. I ran it out of CNG and it ran fine on unleaded for a day, now it has a clicking or percolating sound I can hear from the trunk. The 'check engine' light and the red light on the fuel gauge switch flash in unison with the clicking sound. I took out the 20 amp CNG fuse under the hood and now it runs fine (on unleaded). It doesn't throw a code when we hooked up the scan tool. Thoughts? THANK YOU!

  • #2
    Re: "Clicking noise" near tank

    The clicking sound you hear might be the high pressure lockout valve in the CNG tank. You will hear a click when the valve opens. You should hear one click when you turn the ignition key on. The red light on the fuel switch should come on for a couple of seconds and then go off. First, check if this is happening. Does the car start and then run on CNG before you start to drive? It sounds like there is a loose electrical connection somewhere as repeated transfers from CNG to gasoline usually will set a DTC (diagnostic trouble code) and light the check engine light on the dash if a sensor is causing it. The fact that you see the red light flashing and the clicking indicates that the car is transferring operation from CNG to gasoline and that the AFECU (the computer you think was changed) is still operating---the red light receives power from that computer. I would first look at the wiring for any areas that might be chafed or cut and look at the connectors and relays located behind the drivers headlight (must be removed to access them). When you get the headlight out, start the car and start wiggling the harnesses and see if you can get the problem to occur. There is a 30 pin connector that goes into the coumpter and four relays mounted above it that control CNG operation. Pay close attention to the 30 pin connector. Remove it and make sure that all pins are in place in the connector body and that no pins are bent inside the computer itself. Make sure there is no moisture inside the cavity where it plugs into the computer. When you plug the connector back in, make sure it is fully seated and locked. The AFECU usually fails completely, however someone might have changed this one and not found the underlying problem.


    • #3
      Re: "Clicking noise" near tank

      Was there any CNG smell when it was stalling? Has any one checked the pressures off the LPR?
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      • #4
        Re: "Clicking noise" near tank

        Look on the bright side...clicking is better than ticking.

        If you hear a ticking noise and you have recently informed on a crime boss, run!


        • #5
          Re: "Clicking noise" near tank

          I do know that when the AFECU was replaced, they had to put in a new end clip for the wiring harness due to severe corrosion on the existing one. I will check there, for sure. I will also go back to the tank and do so. I do on occasion smell a whiff of CNG when I am at high speeds and then , say, come to a stoplight. Mostly when the blower motor is on. The mechanic said it was likely just a puff coming out of the vent, so I am just going off of his lead.

          Also, I am curious: Is there a pressure relief valve to purge any pressure left in the system?

          Thanks, you guys...humor, and all.