01 Cavalier blowing up??? Help!!

[morgancox2002]

So here is the problem - see if you can help me diagnose it, it is scaring me.

I have had my CNG cavalier for over a year now, it is a 2001 with 60,000 miles on it. I haven't had many problems but over the past month it has really started deteriorating. First the car started switching over to gas early - it gets down to about 1/4 tank of natural gas and then the next time I start it it starts up on regular gas. It also sprays out natural gas after I fill it up - is sprays for 4-5 seconds out of the fill up valve.

The biggest problem occurred a few days ago and then again today. When I turn the key to start the engine I hear a really loud exploding/whining sound. Last time it happened I took the key back out, looked under the hood, nothing looked wrong so I tried it again and it worked. Today I went to start it up and it did the same thing. I don't even have to crank the engine, just turn the key to the on position and it makes this terrible sound, it really sounds like it is going to blow up. ANY IDEAS??? Please help if you can.

[Lancer Automotive Group]

Re: 01 Cavalier blowing up??? Help!!

Our bet would be a bad high pressure regulator. Just be very carefully that is a lot of pressure there. Give us a call maybe we can help with some advise.

Lancer Automotive
801-268-8863

[afvman]

Re: 01 Cavalier blowing up??? Help!!

Morgan, et al,

Sounds like three problems?

1. Spraying NG during fill up. Bad or stuck check valve at the fill receptacle?

2. Premature switching to gasoline. See Lancers suggestion. Find the pressure sensor for the dash gage. It may be on the HP Regulator and see if that's the problem.

3. 'loud exploding/whining sound'. The 'exploding' part (although we don't like to use that term in this business) or 'loud noise' sounds like an intake backfire. [I have no idea what the 'whining' could be.] If it is an intake backfire, which is not uncommon, there's an accumulation of NG building up in the intake plenum. Could be a leaking injector?

Get a training technician to look at all of these possibilities and let me know how many I hit on.

Good luck,

afvman

[Highmarker]

Re: 01 Cavalier blowing up??? Help!!

Morgan,

Is the "exploding" sound coming from under the hood, or from behind the rear seat? If it is coming from behind the rear seat, then it is most likely a high pressure regulator problem. This is a small "click" sound you hear from the soleniod valve inside the tank when the key is turned on, but it is not very loud. If it is coming from under the hood...I'm not for sure what it could be...maybe the low pressure lock-out???

[siai47]

Re: 01 Cavalier blowing up??? Help!!

If the noise is under the hood and only happens for a couple of seconds after you turn the key on, look carefully around the low pressure lockoff valve and the the line that connects to it. There is a braided section in the line around the back of the engine. When you turn on the key, the lockout valves open momentarily to charge the system. You might be hearing a leak at that time. Don't run the car on CNG (pull the fuse) until you figure this out.

[dovh49]

Re: 01 Cavalier blowing up??? Help!!

It sounds like it could be your fill valve. This is really easy to fix if you have the tools. All you need is the O-ring to replace in the fill valve. You can get an o-ring for free. I don't know if any of the shops do refurbishments but they should since it's so cheap just to fix it. I'll see about posting a how to on fixing the fill valve. I put most of it together a long time ago but never finished it since I didn't want to take mine back apart to take pictures. I guess I'll just post it without the pictures. You do nned a special tool that only a machinist can make but you can jimmy rig the tool. Someone posted it it somewhere on this forum. You'll have to search for that yourself.

I did a how to on how to fix the high pressure regulator (HPR) a while back ago. This is also a pretty easy fix if your up for the work. Below is the link on how to fix the HPR

http://www.cngchat.com/forum/showthread.php?t=1634

Good Luck!

[morgancox2002]

Re: 01 Cavalier blowing up??? Help!!

Thank you everyone for the great suggestions. Just for your information, the loud shotgun like sound is coming from the back of the car, sounds like it is on the drivers side. I haven't tested it a lot because it scares the heck out of me when it happens. It only happens when I am low on NG. Last time it happened I waited a while, tried it again and it started fine on regular gas. I will try the high pressure regulator and let you know if that works.

Thanks

[morgancox2002]

Re: 01 Cavalier blowing up??? Help!!

Yep, high pressure regulator fixed the popping sound. Still no fix on the switching early though. I'll look some more.

[Lancer Automotive Group]

Re: 01 Cavalier blowing up??? Help!!

Our best bet is that you have a bad pressure sensor; it is located on the tank valve.