99 Cavalier Not Always Starting on CNG

[jasonjsimon]

Hi all. I've been lurking in the forum for a while and purchased a bifuel 1999 Chev Cavalier last weekend. The car is in decent condition, but I've had no exposure to CNG before so didn't know exactly what to check for. Anyway when I test drove the car it was just fine running on CNG. On a few drives this weekend I have noticed that it isn't always starting up on CNG. I'd say that it starts on regular gas about 30% of the time. I did refill the CNG tank and the gauge shows plenty of CNG and gasoline, but it still runs on gasoline rather than CNG occassionally. Is there a trick to starting the car up? Do I need to turn on the ignition for a second before starting to allow the computer to check the CNG level first? Are there any other things I can check. I'm pretty mechanically inclined.
Thanks in advance for any help.

[nttrainer]

Re: 99 Cavalier Not Always Starting on CNG

That's pretty common with the 99s. They tend to start on gasoline more often than later years. Something that has worked well for me is to wait and see if the light on the switch goes out when you first turn the key. It it stays on longer than about 10 seconds it will start on gasoline. Just start it on gasoline and drive a couple of blocks. When convenient, turn it off and start it again. If you have enough fuel the light should click off and it will start on CNG. There seems to be a bit of a delay in the sensor realizing that there is enough CNG in the system to run it. A quick start and drive on gasoline seems to take care of it.

There have been some other threads in this section about starting issues with the '99 - '02 Cavaliers. It would be helpful to read through those too.

[jasonjsimon]

Re: 99 Cavalier Not Always Starting on CNG

Thanks for the response.
I've read through this entire Chevy forum, but didn't come accross many threads with the same exact problem. Anyway, I went out for lunch and tried to get it to start on CNG by turning on the ignition for a few seconds and/or waiting for the gasoline light to go off. In this case, the light didn't seem to be going off even after 30 seconds. I started and stopped the car about 4-5 times but it stayed in gasoline mode, so I just drove off on gasoline. I pulled over after going about a block and turned the car off. When I started it back up this time it went right to CNG. On my way back it also started right up on CNG. Very weird.

[nttrainer]

Re: 99 Cavalier Not Always Starting on CNG

That's exactly how mine behaves. That short drive on gasoline seems to do the trick. It starts better on CNG as the temperature warms up. It's less of a problem in the spring / summer.

[jasonjsimon]

Re: 99 Cavalier Not Always Starting on CNG

Okay, I can live with that. This morning I tried the same trick to get the car back onto CNG, but it just wouldn't. The CNG level was at the 1/4 mark, so I went and refilled it and it went back to CNG. I guess there are others that are experiencing the same thing - something to do with a 600 psi threshold. So for me, I could only get about 110 miles out of a full CNG tank - which I can't complain about too much for only $5 of gas. Is that typical?

[Highmarker]

Re: 99 Cavalier Not Always Starting on CNG

I could only get about 110 miles out of a full CNG tank - which I can't complain about too much for only $5 of gas. Is that typical?

Technically your tank is not "full" when you fast fill. There are many reasons for this. The main two are temperature and pressure.

CNG is a gas not a liquid. When you fill your tank up (i.e. increase pressure) you also increase temperature. This increase in temperature makes the gas expand and fill more area in your tank and thus less gas is allowed in. If fast fill (i.e. at a fueling station) and then allow your tank to cool off (i.e. overnight) and then come back and fill again you will get more CNG in your tank. Or you can just slow fill all night long.

If the fueling station is low on pressure, then maybe you only filled to 2,500 psi instead of 3,600 psi. Most fueling stations in Utah have pressure gauges on the dispensor. It is not for sure if the pressure on the gauge is the actual pressure in your tank, but at least it is an indication of whether or not you have a full fill.

You will also need to calculate your actual miles per GGE. You will find that the '99 Cavalier is not the greatest on fuel mileage. It has a 3 speed transmission and a fumigation CNG system. 110 miles per tank is a little under average. I had a '01 Cavalier (4 speed transmission and fumigation system) and I averaged 120 - 140 miles per tank.