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Three different leaking experiences

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  • Three different leaking experiences

    I'm hoping someone can point me to the problem spot with my 01 Cavalier.

    A few weeks ago, as I was getting to an exit I heard what at first sounded like a waterfall, but realized it was leaking CNG, coming from under the hood. I stopped the car immediately and the sound stopped. I waited for the gas to dissipate and started the car again.

    It was fine for a little while and then, while driving on the freeway again, I heard a smaller leak from the trunk area, where the tank is. I also heard a rhythmic popping sound coming from the back. That would stop when I let off the gas and stopped completely when I parked the car.

    At that point I disconnected the cng and took it into Sno-Motion in Utah where they couldn't recreate the issue. So after that I drove through two tanks of CNG and then one day, when pulling into my garage I heard a greater leak again coming from the back, maybe underneath where the HPR is. After a moment of leaking I heard a loud pop back there that scared the crap out of me. Sounded like a tire popping.

    I haven't turned the cng back on since and have another appointment with Sno-Motion to possible replace the HPR, because they think that's the problem. But before I drop down 1000+ to get it replaced I'd like some assurance that it is in fact a problem with the HPR.

    Any thoughts and ideas would be appreciated.

  • #2
    Re: Three different leaking experiences

    You most likely have a HPR failure. The "popping" noise you hear is a relief valve opening and bleeding off excess pressure. The relief valve is located on the HPR which is located just inside of the left rear wheelwell. There are threads on this fourm about changing the HPR for much less money then you were quoted if you are able to do it yourself.


    • #3
      Re: Three different leaking experiences

      I posted this how to before at you can do this for about $250 if you do it yourself. There is a company in Florida that sells them if you would like to order from them (I don't know what the wait time is). Let me know if you want the Florida company info. You can also purchase it locally for about $285, it takes about 3 days to get it from them, that company's name is in the how to. Good luck! Let me know if you have any more questions since I have done this work on my '99. Thunderstik is going to send me some update pictures for newer cavaliers and then I will update the 'how to' to reflect that.