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2000 GMC bifuel CNG. How to switch to CNG and back to gasoline?

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  • 2000 GMC bifuel CNG. How to switch to CNG and back to gasoline?

    I have a question about a 2000 GMC bifuel CNG truck. The truck is a factory IMPCO conversion that was done in 1999.

    I am looking at buying this truck. I am trying to determine if the CNG is operable. I believe the CNG tank was empty (I cannot find a presure guage on the truck). I have filled the cng tank for 3 hours with a FMQ2. The truck has a push button switch on the dash to the right of the steering wheel. When I push the button it rocks upward and springs back to the original position. I noticed that the gas guage changes level when I push the switch (I think to reflect how much CNG is in the CNG tank). The gas guage stays to this position for about 30 seconds and then reverts back to the original level (I think the gasoline level). I think it switched over to CNG after the engine was warmed up. The gas guage would then stay on the CNG level. At this time I pushed the switch again and the gas guage displayed the gasoline level for 30 seconds and then reverted back to the CNG level. I thought that if I removed the fuel pump relay that if the truck was running on CNG it would keep running. When I remove it the truck shuts off even when I think it is running on CNG. I then decided to remove the CNG fuse when I believe it is running on CNG and the truck quit running but would start back up without the CNG fues installed.

    Does anyone know how these factory CNG kits are supposed to work?
    Does the above sound correct? There is a little green light on the rocker switch but it never lights up. When should it light up? I did find another cng switch that has been removed laying in the truck (or maybe it is a new switch?).

    I think that the truck runs like below.
    It seems that the truck starts on gasoline and will switch over to CNG if the engine is up to operating temp after pushing the button (as long as there is ample CNG in the tank). It also seems that the truck wil then run on CNG until the CNG tank is run out of CNG. It will then automatically switch over to gasoiline. There is no missfire or change in RPM when it switches over though.

    The original owned has passed away and left the truck to the daughter so she does not know anything about the CNG. he stickers on the truck refer to a CNG manual supplement. Does anyone know where I can get a copy of this manual? I have searched the internet with no sucess.

    Thanks

    Art
    [email protected]
    907-892-1630

  • #2
    Re: 2000 GMC bifuel CNG. How to switch to CNG and back to gasoline?

    First, many people are confused about what that switch on the dash does. One thing it does not do is control which fuel the vehicle runs on. When there is CNG in the fuel tank and there are no problems with the alternative fuel system, the vehicle will start and run on CNG. The only purpose the switch serves is to determine the fuel level in the non operating fuel system. The more important thing is the light in the switch. When the engine is running (provided the bulb isn't burned out) the bulb will be out when running on CNG and be lighted when running on gasoline. The bulb should illuminate for a moment when the key is first turned on to check the bulb and circuit. If you really want to buy this vehicle, you need to fill the CNG tank and take the vehicle to a dealer who can run a full check on both fuel systems with a Tech2 scan tool to determine the health of the vehicle. You can buy the CNG supplement from www.helminc.com for $30. The item number is GMT00CKNGV.
    Last edited by siai47; 07-19-2009, 08:05 AM. Reason: additional information

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    • #3
      Re: 2000 GMC bifuel CNG. How to switch to CNG and back to gasoline?

      Hi I also have a 200 bi fuel chevy pu. If you would like to check the cng just start the truck and watch the fuel level then shut it off count to ten and restart and if the fuel level is different then the truck has switched over. The truck will always pick the cng first but sometimes it doesnt and you have to restart it like I described. You can also remove the fuel relay in the box under the hood and make sure the two cng fuses are there and start the truck. if it runs then the cng works and you are ok. If you have any other questions let me know. thanks brent

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      • #4
        Re: 2000 GMC bifuel CNG. How to switch to CNG and back to gasoline?

        Hello I know this is an old post but I am hoping someone will respond. We just bought a 2004 Chevrolet Express 2500 bifuel and are so excited about CNG. But I have a question. Does The CNG not work well in cold weather. We live in Eastern Utah and have pretty cold winters. When we brought the vehicle home it did fine, but now it won't run on CNG. I have tried starting it up, warming it up and turning it off to try again. When I restart it, it starts up fine, but the check engine light comes on and it continues to run on gasoline. Is this just because it is cold outside, or do we have other problems. Is there a filter or something that we need to check? I am afraid we bought a bad vehicle for our climate. Please help! Thanks so much!

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        • #5
          Re: 2000 GMC bifuel CNG. How to switch to CNG and back to gasoline?

          Originally posted by newbie9 View Post
          Hello I know this is an old post but I am hoping someone will respond. We just bought a 2004 Chevrolet Express 2500 bifuel and are so excited about CNG. But I have a question. Does The CNG not work well in cold weather. We live in Eastern Utah and have pretty cold winters. When we brought the vehicle home it did fine, but now it won't run on CNG. I have tried starting it up, warming it up and turning it off to try again. When I restart it, it starts up fine, but the check engine light comes on and it continues to run on gasoline. Is this just because it is cold outside, or do we have other problems. Is there a filter or something that we need to check? I am afraid we bought a bad vehicle for our climate. Please help! Thanks so much!
          I also have a 2004 Express bifuel but I don't have a lot of experience driving it in really cold winter weather yet to know whether at a certain low temperature, it will default to gasoline like some of the Fords (13° F. according to Ford literature). Nothing in the CNG manual says that low temperature is an issue while starting but it IS harder to start on CNG when it's cold out. And, the Chevy is designed to start on CNG but will default to gasoline if the engine starter turns over more than 4 seconds without starting. So if your ignition system isn't performing 100% it may not start on CNG when cold. But you would think when you warm it up on gasoline and then try to restart it on CNG that it would run. If the Check Engine light is coming on then there must be a problem somewhere that is setting a diagnostic trouble code. You may want to have a CNG-capable shop pull the codes with a Tech2 (or equivalent) scanner and find out what is going on. Also, check fuses 21, 23, 33, 35 & 63 in the fuse block located in the engine compartment to see if one of them is blown.

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          • #6
            Re: 2000 GMC bifuel CNG. How to switch to CNG and back to gasoline?

            I did get manual on ebay for 10 dollars, you just half to keep checking .

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            • #7
              Re: 2000 GMC bifuel CNG. How to switch to CNG and back to gasoline?

              Originally posted by a1hotwash View Post
              I did get manual on ebay for 10 dollars, you just half to keep checking .
              I advise anybody looking for something on eBay to use the "save this search" option for the item they are looking for and subscribe to "email me daily" so that eBay will automatically notify them whenever the item is placed up for auction...

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