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2001 Cavalier new owner CNG questions (problems?)

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  • 2001 Cavalier new owner CNG questions (problems?)

    So I took the plunge and bought a 2001 Cavalier with 116k miles. It runs great on both gas and CNG, but I am have a few questions about the CNG issues I have experienced. For the climate curious, I live Northern California, and my vehicle is garaged when not driven (whether at work or home).

    1. On CNG, the car starts on the first turn of the ignition, but only when the car is cold (sits overnight or longer than 8 hours). If I turn the car off and re-start it, it takes 6 seconds or so to start. After starting the car runs smoothly,with no sputters, misses, or anything else that feels like a poorly tuned engine.

    2. I have never managed to get more than 3.676gge into the car, which was a full fill at the County maintained pump. The pump has a digital display with a 0-100% fill gauge, so I assume that when the digital display reads "full" I have a full tank. I run the car on CNG until it automatically switches over to Gasoline, so I wonder why I am not getting the 6.2gge that I read in the specs. Temperature today was 45 degrees when I got the 3.676gge in the tank (most to date).

    3. Not sure if this is related to #1+2, but the gas gauge seems to go down quickly. I am getting about 21mpg on CNG, but it's frustrating that I'm getting a longer range.

    Any help on the above issues are well appreciated in advance. The car is in great shape, leaks no oil, or has any other annoying gremlins. The CNG items above are concerning to a newbie like me, but I would really like to be educated more than anything else.


  • #2
    Re: 2001 Cavalier new owner CNG questions (problems?)

    The starting issue sounds like a normal 2001 Cavalier to me . First, on a warm start (because it is a fumigation system) there is usually a little residual gas in the intake system. This gets the mixture a little out of wack (rich) when you shut it off and then try to restart. Over time the gas dissipates and the restarts are a bit easier. Just leave your foot off the accelerator and hold the key to "start" until the engine is running smoothly. 21 mpg is OK but on the low end for mixed driving. Highway should be several mpg better. Cold weather, rain/snow and underinflated tires will affect a CNG car just like it does a gasoline car. As to 6.2 gge capacity, 5.5 gge would be a much better target. On a slow fill (which will get you a more complete fill) you should be able to get between 5 and 5.5 gallons in the tank. Your highway range should be about 150 miles to changeover and city range as low as 120 miles. Questions---is the fuel gauge going all the way to empty (including the "check gauges" warning) before changeover? Also is the fuel gauge past the full mark after you complete your fill? Under 4gge is very light for a Cavalier fill. Usually with a full fill the fuel gauge will stay on full for 20 miles or so before starting its rapid descent. Without looking at actual tank pressures, it is hard to determine why you can't get a full fill. In rare cases, the tank can have some unwanted liquids (water, oil, etc.) that displace some of its capacity.


    • #3
      Re: 2001 Cavalier new owner CNG questions (problems?)

      Update: Well, I've filled up 2 more times since my last post, and the fills have gotten better each time. 4.2 GGE on the 12/14 and 4.9 GGE on 12/18 (tonight). Also, the hard starting (cranking for 5 seconds to start) is now once every 5 warm starts instead of every warm start. I'm guessing that being driven every day is getting the car back in shape. The Cav sat for about 6 weeks before I bought it, and it was being run mostly on regular gas before that. I am really happy with the developments over the last week....knock on wood