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  • Cavalier Venting From Rear

    My 2001 cavalier is venting from under the rear in cold weather. It sounds like a paint ball gun. It starts when I turn on the key. If I pull the cng fuse it starts on gasoline and runs fine. Any ideas?

  • #2
    Re: Cavalier Venting From Rear

    habilis1,

    It sounds like it is the high pressure regulator. I have a friend how had the same problem in his 1999 Cavalier. At first we thought it was the pressure relief valve, but that did not fix it. He finally replaced the high pressure regulator (I've heard those are expensive), and that fixed it.
    Jared.
    Mountain Green, Utah
    2003 CNG Cavalier
    2003 CNG Silverado 2500HD

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    • #3
      Re: Cavalier Venting From Rear

      Try to listen and locate the leak then spray some soapy water at the site to see if it's in a fitting or a failed component. I haven't been under mine yet to see what's back there along the fuel delivery line but I believe the filter is back there somewhere. Keep us posted on what you find.

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      • #4
        Re: Cavalier Venting From Rear

        If you lower your back seat, you will see a large black rubber hose going from the tank to the floor. Inside this rubber hose where it meets the floor is the high pressure regulator. You can also see the high pressure regulator from underneath the car located by the driverside rear tire. Check and see if this is where the noise is coming from.
        Jared.
        Mountain Green, Utah
        2003 CNG Cavalier
        2003 CNG Silverado 2500HD

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        • #5
          Re: Cavalier Venting From Rear

          Most of the time when you have venting from the Pressure Relief Device (PRD), the High Pressure Regulator is to blame. The IMPCO HPR3600 is known for having discharge pressures in excess of the set pressure of the PRD, most of the time 250 psi. Almost all of the OEM designed systems incorporate an electronic shutoff valve at the fuel pressure cylinder, when the ignition is off, the fuel is usually off, making one notice the "popping" when the key is switched on, my advice is to have a qualified shop replace the HPR with the proper unit and then see what other issues rise up. I have a couple of new HPR3600's here in AZ, if interested, Kevin

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          • #6
            Re: Cavalier Venting From Rear

            I agree with the above comments. My 2000 was doing the exact same thing. Replacing the High Pressure Regulator fixed the problem. Verify the leak as mentioned above. When it's venting, crawl under the car and look directly above the muffler (at least that's where it is on my 2000). You'll see the HPR there. Mounted on the side of it is the thumb-sized brass relief valve mentioned earlier. The popping sound is likely the relief valve opening. I also thought the relief valve might be bad, and found some on e-bay with the same part number. Replacing it didn't help, but replacing the entire regulator did.
            2000 Cavalier

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            • #7
              Re: Cavalier Venting From Rear

              I had the same problem but I don't think it had anything to do with cold weather in my case. I turned the manual shut off valve located on the side of the tank a few turns (closing) with an alan wrench. The next time I started it up it worked fine. Sorry I can't explain why this worked but hope it helps

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              • #8
                Re: Cavalier Venting From Rear

                What are the part numbers for the High Pressure Regulator and the Pressure Release Device?

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                • #9
                  Re: Cavalier Venting From Rear

                  I took my car in to have the HPR diagnosed and replaced, so I don't know the part number for it. The PRD part number is: PV3865 Made by Sherwood

                  As mentioned earlier, I found some on e-bay. I bought them since I found out (after removing the PRD and testing it on my garage compressor) that it leaked with just 100psi on it, even though it's rated at 400 psi. It still didn't fix the problem, so I opted to just replace the whole HPR.
                  2000 Cavalier

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                  • #10
                    Re: Cavalier Venting From Rear

                    Mine is venting directly out of the nozzle where you fill it up right after the tank is filled and then it doesn't switch to CNG. Any ideas? (it is a 1999 Cav)

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                    • #11
                      Re: Cavalier Venting From Rear

                      Mickael,

                      That sounds like it is the check vavle. I have had that happen a few times with my '01 Cavalier. When I notice it venting out of the fill nozzle right after I fill up, I put the filling nozzle from the dispensor back on and pressurize the system then depressurize the system and remove the filling nozzle and then it stops leaking out the fill nozzle on the car. Of courese, the last time I had to do this, I had to did it several times to finally get it to stop leaking.
                      Jared.
                      Mountain Green, Utah
                      2003 CNG Cavalier
                      2003 CNG Silverado 2500HD

                      Comment


                      • #12
                        Re: Cavalier Venting From Rear

                        I had a similar problem on two different occasions in my 2001 cavalier. After fueling, there appeared to be slight ice build-up in the fuel receptacle and it failed to close completely allowing lots of gas to vent. In both cases though it only lasted half a minute or so (just long enough for me to start to panic) before it corrected itself. Once, I just re-attached the filling valve, and then when I removed it it was fine. If you are experiencing this constantly I would definitely get it looked at, I would assume the seal must have gone bad, or maybe the spring mechanism...

                        good luck though,

                        KIRK
                        Last edited by kirkbenge; 02-12-2008, 07:46 PM.

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                        • #13
                          Re: Cavalier Venting From Rear

                          Hi Mickael,

                          Did you ever get this fixed? Mine leaks when I start it up or turn it off. Also, when I step on the break it will make all types of noisy leaking sounds.

                          Thanks.

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                          • #14
                            Re: Cavalier Venting From Rear

                            No I have not taken it in yet. It did it again just today. Actually it did both things listed in this treat. It vented from the nozzle where you fill it up. (I tried the recommendation of attaching the nozzle again and pressurizing the system and then vent and remove it. After a few tries it worked.

                            Then driving it made the "paintball gun" noise described in this forum and vented from the high pressure regulator. I think it is time to get the system looked at. I will look at the forums for recommendations on good CNG mechanics in Salt Lake. If anyone wants to makes suggestions here they would be appreciated.

                            Thanks!

                            Comment


                            • #15
                              Re: Cavalier Venting From Rear

                              There's only one legal place (you have to be certified to work on CNG systems, if you're a mechanic) to take it in Utah that I know of and that is SnoMotion. Phone: # 801-281-4766.

                              I was going to take mine off and see if I can figure out what the problem is and see if I need to replace it or not (they're $400, I believe so I hope I don't need to).

                              It sounds like you're having the same problem I'm having. I'll let you know once I get it fixed. If you beat me to it let me know. I should get mine done within two or three weeks.

                              Does anyone on the forum know where I could get new seals? The CNG repair manual says any time you disconnect parts you should put a new seal in. Don't know if it's really necessary but I would like to go by the book, even if they're a dollar a pop.

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