Cavalier CNG only starts after pulling and replacing fuse.

[jclancy]

I have a Bi fuel Chevy Cavalier 99. Not sure what kind of CNG kit is on it but i know it was factory installed. This vehicle was an ex fleet car. My problem is that it was running great, then suddenly it would not turn on with CNG anymore. All it wants to do is turn on with Gas. even after i have switched off the engine from starting from gas the light stays on wanting to start on gas. But i found that if i pull out the CNG Fuse from under the hood. start the engine then switch off and put the fuse back it will then start on CNG.

I have replaced the fuse now and still this problem occurs. Once on gas or CNG the car runs great.

Help!!!!!!!!!!!!!!!!

[John Mitton]

Re: Cavalier CNG only starts after pulling and replacing fuse.

Welcome to CNGchat jclancy!
I will move this over to the GM Forum for the experts to chime in there.

[Highmarker]

Re: Cavalier CNG only starts after pulling and replacing fuse.

jclancy,

Allow me to explain a little bit about the CNG system on the Cavalier.

The light indicator/switch on the dashboard next to the dome light switch works in the following manner. If you are running on CNG and you press the switch it will show the level of fuel in the gasoline tank. If you are running on gasoline and you press the switch it will show the level of fuel in the CNG tank. The switch is only for checking the level of fuel in the tank you are not using at the current time.

Now onto the light. The light will come on momentarily at start-up. This is part of the check system that the alternative fuel control unit (AFCU) and the light are working properly. If running on gasoline, the light will stay on. If running on CNG, the light will go off. If you pull the CNG fuse from under the hood, you are essentially shutting off the AFCU and therefore it is not working. With the AFCU not working, the light will be OFF and you will be running on GASOLINE. In other words, pulling the CNG fuse makes the car run on gasoline with the light on the dashboard off.

Couple of things to check.
1. Make sure there is CNG in the tank. The car is designed to run on CNG until it runs out of CNG at which time it will automatically switch over to gasoline. The car will not run on CNG again until you put CNG in the tank.
2. If there is CNG in the tank, make sure that when you turn the key to the "ON" position you hear a "tink" coming from behind the rear seat. This is the tank valve opening to allow CNG to flow to the engine. If you don't hear a "tink", then most likely your tank valve is bad or you have a bad connection.
3. If you hear a "tink", come back and let us know...your problem could be from a number of components.

[jclancy]

Re: Cavalier CNG only starts after pulling and replacing fuse.

Thanks for the reply. I had a 1/4 tank of CNG fuel after refueling the car it went back to working, I guess there was just not enough pressure in the tank. i don't what to say. But it is working as long as i keep it above the 1/4 tank mark. we will see how it all goes.

[Highmarker]

Re: Cavalier CNG only starts after pulling and replacing fuse.

jclancy,

You might want to look back in this forum (GM/Chevy Forum). There have been some other people that have had the same problem of the car switching over to gasoline when the CNG tank gets to 1/4.

[siai47]

Re: Cavalier CNG only starts after pulling and replacing fuse.

The Cavalier is designed to switch over to gasoline when the tank pressure goes below 200 PSI--when the car is running on CNG. If the car is shut off and then restarted and the tank pressure is below 600 PSI, it will not switch back to CNG until the tank pressure exceeds 600 PSI

[Philster]

Re: Cavalier CNG only starts after pulling and replacing fuse.

jclancy,

Allow me to explain a little bit about the CNG system on the Cavalier.

The light indicator/switch on the dashboard next to the dome light switch works in the following manner. If you are running on CNG and you press the switch it will show the level of fuel in the gasoline tank. If you are running on gasoline and you press the switch it will show the level of fuel in the CNG tank. The switch is only for checking the level of fuel in the tank you are not using at the current time.

Now onto the light. The light will come on momentarily at start-up. This is part of the check system that the alternative fuel control unit (AFCU) and the light are working properly. If running on gasoline, the light will stay on. If running on CNG, the light will go off. If you pull the CNG fuse from under the hood, you are essentially shutting off the AFCU and therefore it is not working. With the AFCU not working, the light will be OFF and you will be running on GASOLINE. In other words, pulling the CNG fuse makes the car run on gasoline with the light on the dashboard off.

Couple of things to check.
1. Make sure there is CNG in the tank. The car is designed to run on CNG until it runs out of CNG at which time it will automatically switch over to gasoline. The car will not run on CNG again until you put CNG in the tank.
2. If there is CNG in the tank, make sure that when you turn the key to the "ON" position you hear a "tink" coming from behind the rear seat. This is the tank valve opening to allow CNG to flow to the engine. If you don't hear a "tink", then most likely your tank valve is bad or you have a bad connection.
3. If you hear a "tink", come back and let us know...your problem could be from a number of components.

Jared,

I have a similar issue... I have a full tank.... I do hear the clink when I turn on the key but the light does not go out. What components should I check? I live in Central Utah so it is not like a small thing to come up to SLC to have it looked at, but I am willing if I can't find a resolution. I am mechanically oriented and am willing to take things apart. I also have a 2000 cavalier that runs great so I can swap parts if needed. I do need instructions and guidance if you would be so kind. Thanks

Phil

[siai47]

Re: Cavalier CNG only starts after pulling and replacing fuse.

You must have refueled to assure you have a full tank. Try starting the car and after it is running with the red light on, press and hold the fuel switch for a couple of seconds to see if the fuel gauge starts to move. If it is moving towards empty it is possible the fuel pressure transducer has failed or is stuck. The "tink" or "clink" you hear is the high pressure lockoff valve opening to prime the fuel system. At that point the transducer is pressurized and if there is 600 psi at the transducer, it will allow CNG operation. A system check is also performed by the AF ECU when the ignition is first turned on but it would set a code and a check engine light if it failed the test. So, see what happens and report back.

[lylepoulsen]

Re: Cavalier CNG only starts after pulling and replacing fuse.

I really appreciate this thread. The part about the "tink" may be the solution to my 01 Cav blowing the cng fuse. I cannot hear the "tink". Is that because that valve is trying to open and draws to much power resulting in a blown fuse before it can "tink"?