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2001 Cavalier noise issue

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  • 2001 Cavalier noise issue

    I have never owned bi-fuel CNG vehicle. I just bought a 2001 Cavalier and filled it with about 6 gge. It had been ran previously mostly on unleaded regular, I think. After filling, it switched to CNG and ran fine. At $2.12 gge I thought it was great. No problem stopping and restarting the car. Next day after sitting overnight in cold weather, I thought the car was going to explode. A loud venting or popping noise seemed to come from the fill nozzle/ tank area just when the key was turned on, no starter being engaged, just the key moved to the on position. This happened for two days but only prior to the initial morning start. It seemed to not happen after the third day but I only had half a tank of CNG left. The Chevy dealer wants $120 just to check it out but I'm not sure I have a problem or was it just a sticking regulator. Since it is over 50 miles to the closest Fill station, I have ran 3 tanks of unleaded after the empty CNG switchover and not sure if it will do the same thing when I fill it with CNG again. Any advice other than dishing out $120 and go to the dealer.

  • #2
    Re: 2001 Cavalier noise issue

    The noise you hear is most likely the high pressure regulator (HPR) relief valve venting. This happens when the HPR sticks or fails. It is located under the car near the left rear wheel. There is no problem with re-filling the CNG tank to see if it happens again. Sometimes, the HPR will clear itself, or on occasion, the regulator has failed. After refill, turn on the ignition switch to see if the noise happens again--the noise should be a popping sound, not a continious hissing sound. If you hear either, turn off the ignition switch. Otherwise start and drive the car as usual and monitor the situation. If the noise happens immediately on the re-fill or happens again, remove the fuse marked "CNG" in the fuse box behind the battery to prevent CNG operation and the noise will stop. There are several members on this site that can provide a new HPR and/or install one if you are near their area. And remember, you are already $120 ahead because you know what's wrong !

    BTW--this is problem is sometimes caused during cold weather from mositure in the natural gas fuel causing the internal parts of the regualtor to freeze up. In your case, you mentioned the first start in the morning was the only problem. After you run the car, antifreeze from the cooling system goes through the regulator warming it up, thawing it out. You could test this by pulling the CNG fuse in the morning and replacing it after you have run the car for a while and see if that changes the problem.
    Last edited by siai47; 01-09-2010, 08:17 AM. Reason: note about freezing operation.

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    • #3
      Re: 2001 Cavalier noise issue

      Where in Washington are you?
      2002 Cavalier
      2003 Cavalier
      2004 Cavalier

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      • #4
        Re: 2001 Cavalier noise issue

        I live in the Tri-cities area in eastern WA. I am visiting the Sacramento area and that is where I get my CNG.
        I will try to refill with CNG again tomorrow. What is the difference between the popping noise and the constant hiss and I have encountered both but neither last over a minute.

        Thanks
        Last edited by nibac; 01-11-2010, 08:40 PM.

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        • #5
          Re: 2001 Cavalier noise issue

          I used to live in Seattle, and moved to SLC, Utah last year. I've driven through the tri-cities numerous times, and hope they get a filling station sometime!
          2002 Cavalier
          2003 Cavalier
          2004 Cavalier

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          • #6
            Re: 2001 Cavalier noise issue

            i just had the same issue, at below zero here in n. utah I had the car on ramps just about to change the oil and the car running for several minutes starting making a noise like it was going to explode. I shut it off, pushed it off ramps, then noise went away. put it back on ramps, changed oil/filter, car was fine, moved out of garage and the next morning car did same noise. it automatically switched to gasoline and is fine, when warm switched back to cng and it is fine, did it two mornings in a row but real cold temps here, manual says problems can occur if below 10 degrees farh. Im hoping its just the cold weather, will run gas only for a month or so and hopefully will resolve issue due to temps?? how much is part and labor if this continues to occur? any good cng mechanics in logan, ogden or slc. utah?

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            • #7
              Re: 2001 Cavalier noise issue

              You are experiencing freezing in the regulator due to mositure in the natural gas. As I posted earlier on this thread, the regulator is sticking either shutting off the supply of CNG or allowing too much CNG to flow which activates the PRD (pressure relief device) on the regulator. Until the regulator gets warmed up by the engine coolant or the moisture level in the gas reduced this will happen in very cold weather. There is nothing wrong with your Cavalier, its just the way it is .

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