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'01 Cav Probs with CNG and Reg Gas

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  • '01 Cav Probs with CNG and Reg Gas

    Fist off, greetings to everyone in the forum, this looks like a great place to get info about my car.

    I have an '01 Cavalier that has run great since I bought it in January, it had 47k miles on it. Car ran perfect on CNG and regular gas, nothing strange about the car.

    First Problem:
    Within the last month and a half the car has started having problems starting on CNG. The car would at random start on regular gas or CNG. It seemed to me like it would just skip the check process of whether or not there was CNG in the tank and go strait to regular gas. I could see the indicator light on the dash wouldn't come on for the few seconds like normal and would stay off (indicating it was on CNG) but it would run on regular gas even though I know the CNG tank was 3/4 the way full.

    Second Problem:
    So I am driving the car home Christmas Day and near my home the car dies and refuses to start again. It was running on regular gas, and I know it has 1/4 of a tank of regular gas but it refuses to start. I removed the battery cable and let it sit overnight, plugged it back in and tried it to see if that would make a difference but nothing. After the car sits for a little while, I can try starting it and it will seem like it wants to start but doesn't run more than a turn or two. It seems to me like it isn't getting fuel, but that is just my guess.

    I'd like to fix this on my own. I have access to a full shop and some close friends that are mechanics that will let me bother them with questions, but none of them have much experience with CNG. If anyone could give me some guidance on what I should check to weed things out and narrow down what is happening to my car, I would very much appreciate the help.

  • #2
    Re: '01 Cav Probs with CNG and Reg Gas

    Try removing the fuse marked "CNG" in the fusebox under the hood and see if it will start and run normally on gasoline. If that works, then there are a couple of other things to check. With the fuse removed, there will be no indicator light on the fuel switch and it will be trying to start right away on gasoline. This will tell if the problem is in the gasoline system or some other common system and will rule out the CNG system. Report back .

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    • #3
      Re: '01 Cav Probs with CNG and Reg Gas

      Originally posted by siai47 View Post
      Try removing the fuse marked "CNG" in the fusebox under the hood and see if it will start and run normally on gasoline. If that works, then there are a couple of other things to check. With the fuse removed, there will be no indicator light on the fuel switch and it will be trying to start right away on gasoline. This will tell if the problem is in the gasoline system or some other common system and will rule out the CNG system. Report back .
      A friend of mine suggested just putting regular gas in the tank (I didn't think it needed gas since the dash gauge said it had a quarter of a tank), but that fixed it. Car started right up and works great. So I am thinking my fuel sensor is bad as far as gasoline goes. I'll look more into that.

      That narrowed my problem down real quick though. But that doesn't help with the problem I am having with CNG. What would you suggest I check next now that my car is running on gasoline again?

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      • #4
        Re: '01 Cav Probs with CNG and Reg Gas

        OK, now that you are running on gasoline--lets see why it doesn't run on CNG. First, does it try to start on CNG, I.E. does the red light on the fuel selector come on when you turn the key on and then go back off? Next, does it start right up on gasoline or do you have to crank for 8 seconds before it starts on gasoline? When running on gasoline, is the red light in the fuel selector switch on and what happens when you press and hold the fuel selector switch? Does the gauge move to reflect what you think you have in the CNG tank? Can you now get the CNG tank refilled and see how much fuel it takes to fill? Is the "check engine" light on? This will help narrow a couple of things down---Report back !

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        • #5
          Re: '01 Cav Probs with CNG and Reg Gas

          I have been having the same problem... as far as it not running on NG, when I start up the car it goes straight to gas not even trying the NG. It doesn't do the red light at all and I have checked the fuse and it is still good. When I bought my car about a year and a half ago it didn't show how much NG was in the tank but this has not caused a problem before.
          I also have a '01 Chevy Cavalier.
          Thanks for your help

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          • #6
            Re: '01 Cav Probs with CNG and Reg Gas

            To member DSteenblik, If the red light never comes on when you first turn on the ignition and the fuse is OK, then you have one of two problems. The cheap problem is that the bulb could be burned out in the switch. The expensive problem is that the AF ECU is malfunctioning. If the ECU is functioning and has power, it always does the bulb check. You also stated that the fuel gauge didn't read CNG levels but ran OK on CNG. If this is the case, the tank pressure transducer may have failed and the ECU may think there is no CNG in the system and goes directly to a gasoline start. Take the car to a dealer and have them scan it. Verify that the AF ECU can be accessed. If it can, it is working. With the scan tool, they should be able to force the bulb to light to confirm if it is good. Next have them access the data screen and look at the fuel pressure the transducer is reporting. If it is under 600 psi, the vehicle will not try to run on CNG. If the tank isn't full, try filling it as sometimes the transducers stick and the pressure change might get it moving again. If you live in an area where there is corrosion from road or sea salt, and the AF ECU appears to be dead, you should remove it, check the connectors for any corrosion and clean them. Also, this system requires good grounds to operate correctly. Look at all the ground wires around the ECU and battery area. Remove the grounds, clean and re-install them and spray a protective coating over them.

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            • #7
              Re: '01 Cav Probs with CNG and Reg Gas

              Siai47-
              Thank you for your help.... The problem turned out to be different than both of those solutions. My low lights on my drivers side went out and it was an electrical problem. While fixing it we found some of my wires were not connected to the ground and this was causing problems, We fixed the wires and the ground and now everything is working like it was before.
              I think its great that I was able to get this fixed while working on other problems cause now I feel like I got my moneys worth trying to get another problem fixed.

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