2001 Cavalier Won't Start

[SoCalCav]

I bought my Cav 5 yrs ago and every once in a while it has chortled and stalled at start up or been slow to start in CNG "mode". This was probably about 10-20% of starts. According to the manual this was somewhat normal.

About two weeks ago I started getting really hard backfires from under the hood while driving. The first time it happened, I pulled over thinking I ran over something. This happened while accelerating.

This type of backfire continued sporadically for the next few days. One backfire per episode, maybe every other day with it causing the engine to stall once. Next the backfiring began to happen with each start up. Finally, the engine would not start, unless I pumped the throttle vigorously and kept the key turned for more than a minute.

I took the car to my mechanic, he initially replaced the ignition coils and the plugs. It seemed improved but by morning the same thing all over again. Today we swapped out the battery, but still had the problem. So we pulled the 20 amp CNG fuse and so far so good.

Assuming the problem remains "fixed" when running on gasoline, any thoughts as to why the CNG system is acting up? Do these symptoms seem familiar to anyone? I'd like to trouble shoot and correct this myself. Heck my mechanic, having no previous experience with a NGV, would love to hear how this story ends.

Thanks to any help you may offer.

Mark

[siai47]

Re: 2001 Cavalier Won't Start

Sounds like no fun. You say your mechanic replaced the coils and plugs. Did he replace the spark plug wires? The wires themselves are usually the cause of backfiring problems (if it is ignition related). Make sure the wires are routed properly, all retainers are in place and there is wire loom around the wires where they pass between the cylinder head and the engine lift ring by the ignition coils. The factory loom in this area usually is falling apart due to heat and needs to be replaced. The loom is just a piece of split plastic covering that covers many kinds of wires used in car wire harnesses and is available at any auto parts store. With all the backfires you have had, you need to check the induction system to be sure you haven't blown out the air filter, or broken the cover to the air cleaner box. Remove the screws holding the cover in place and check the cover for cracks. Also check the body of the air cleaner where the screws thread in to make sure there are no cracks around them. If something is broken, any late model Cavalier air cleaner will replace the CNG unit (they are the same). Also inspect the rest of the hoses from the air cleaner box to the throttle body on the back of the engine. Make sure the hoses and clamps are in place and tight. Any leaks in the induction system will lead to hard starting and backfires. As a final note, if everything is working correctly, "pumping the gas" will not help the car to start. You must leave your foot off the accelerator pedal to allow the proper flow of natural gas into the induction system. Pushing on the pedal in a normal start helps create a lean condition the increases the risk of backfire . If these things don't change or fix the problem---come on back for more advise.

[kirkbenge]

Re: 2001 Cavalier Won't Start

I agree with siai47, It is most likely related to plugs/wires. When your mechanic replaced your plugs, he should have replaced the wires as well, if not, start there.

Also did he use the "bi-fuel" recommended plugs? The first time I changed my plugs I went to Autozone and got the recommended plugs for my cavalier, the employee didn't mention that there was a plug with a different gap recommended for bi-fuels. I started having backfire issues within a very short time, and when I went back to Autozone and mentioned that I had a bi-fuel, low and behold, they have a plug specifically for that.

I also wanted to reiterate checking your air filter housing. Mine shattered when I was having backfire issues, have a look at yours and see if it has been damaged.

[SoCalCav]

Re: 2001 Cavalier Won't Start

Thanks for your reply. My mechanic did inspect the air filter and it was cracked (and therefore replaced). No the plug wires were not replaced. It is running well on gasoline (though it makes me sick) so am I correct in thinking the plug wires are ok. I'll check the plugs he put in (re:kirkbenge comment).

I'll check the loom and hoses this week. Thanks for the tip on the accelerator at start up.

Thanks again,

Mark

[siai47]

Re: 2001 Cavalier Won't Start

No, the plug wires are most likely not ok and are the most likely cause of your problem. Even if they look good, replace them with the factory set, or the best aftermarket set you can find. CNG operation requires a lot higher energy spark to ignite the mixture then gasoline. Wires no longer have a solid core and over time can break down internally or start to leak through the covering insulation to ground. The car can run fine on gasoline and then misfire on CNG. A GM Tech2 scantool even records misfire data for each cylinder so you can find the number of times it is happening. I've watched this happen--there is no misfire data on gasoline and then switching to CNG the misfires start to show up. I am suprised that your mechanic decided to change the plugs and coils but not the wires. Again, the routing of the wires, use of all the factory retainers and wire loom is important. Also, as Kirkbenge noted, be sure the correct plugs (and gap) are in the vehicle .

[kirkbenge]

Re: 2001 Cavalier Won't Start

I agree with siai47. I've seen it happen more than a few times. The single most likely cause of your problems is your wires. Do that first. Running fine on gasoline doesn't mean anything. Change the wires first and then if you're still having issues you can look at other possibilities, but you probably won't need to.

[SoCalCav]

Re: 2001 Cavalier Won't Start

Thanks again for your replies. I will try to swap out the plug wires and verify the plugs this week. I really appreciate the expertise.

[goodforyou]

Re: 2001 Cavalier Won't Start

Ours did the same thing....In the beginning the car was just hard to start. Eventually, the car ceased to start at all. We replaced the gas mass sensor. The car starts now, but it is still hard to start. We are going to replace the low pressure regulator and see if that helps. I'll let ya know. We are experiencing a major heat wave (105 today) and we are waiting for it to cool off before working on it. Should be this weekend.

About the ignition, there is a recall on the starter. Something about a thermal event. The starter can catch on fire. I don't know if that's related to your problem, just thought you should know.

[siai47]

Re: 2001 Cavalier Won't Start

This is going to take this a little off topic , however a couple of replies to the last reply are in order. First, on the question of the "thermal event" (i.e. fire ) the recall involves adding a relay to the starter circuit to take the load off the ignition switch. The relay is located on a new wire harness which is attached near the starter motor. If you don't see the relay, take the car to a Chevrolet dealer and let them check to see if the recall has been done according to their "VIS" system. They can also look for the relay. As to hard starts---many people overlook this one. There is a service bulletin about the low pressure lockoff valve. If the GMS/MCV is working O.K. the problem can be the valve. Here's why---When the igniton is turned on, the High pressure lockoff is opened, the low pressure lockoff will not open until the ECU senses 25 rpm of crankshaft rotation. With the voltage drop caused by the starter (and maybe a not so perfect battery) there just isn't enough umph to open the valve. The SB says to replace the valve. I would check the battery, cables and grounds first before condeming the valve. Anyway, it's worth a look.