Backfire

[siai47]

Just purchased a 2002 Cavalier. The aircleaner housing was fractured and unfortunately because of this the engine was getting unfiltered air into the intake system. My question is---how many of you have experienced a backfire in the intake system. I have a 2000 Cavalier and have not had a problem and it appears to have a standard air cleaner. However the 2002 car was fitted with an air cleaner that had a couple of "blow off" valves to keep the pressure from building up and breaking the housing (didn't work). The dealer told me that these air cleaners were fitted under a service policy to owners that complained about the backfire and blowing up the air cleaner. The policy number is 04008. The air cleaner cover that is fitted with the valves is P/N 52372980. I don't know what causes the backfire or when it occurs as I have never experienced it. It must be a problem if GM came up with a fix for it. BTW the valves installed on my car interfered with the hood inner panel and someone gave it clearance with a hammer.

[Kevin Fern]

Re: Backfire

Backfire's are caused by a lean condition, ie. there is enough heat left over in one or more cylinders that can ignite the incoming air/fuel charge on a lean condition. This is a problem when the fuel is introduced through fumigation, the nature of the backfire and the damage that it can cause can be quite large, because the entire intake manifold is filled with a air/fuel combo. I would take the vehicle to a facility who works on these types of systems, Kevin

[soarhead25]

Re: Backfire

My 98 Cav had an intermittent backfire condition that was worse on heavy accell. The biggest backfire blew up the air filter box!

As AFV Tech pointed out, a backfire in the intake side of the engine typically indictates a lean fuel mixture engine condition, and a backfire in the exhaust system would typically indicate a rich fuel mixture engine condition.

Now my backfire was only present while running on CNG, and not gasoline, which was pointing me to check my cng fuel system. (Filters and such)
However, after reading the backfire symptom chart in the GM Cavalier repair manual, it states that since CNG is a gaseous fuel, it requires much more KV to jump the spark plug gap and ignite the cng/air mixture. After removing the spark plugs I had found a light carbon track on #1 spark plug that was causing the misfire. I replaced them with generic autolites and have not had a problem with them yet, although I really like to replace plugs with oem.
Check your spark plugs and wires!

I also came across a GM bulletin for #4 spark plug wire going bad, but didn't research the bulletin to see why as of yet.

[siai47]

Re: Backfire

Thanks guys for the replies. I ran a scan on the car with a Tech2 and haven't found anything out of spec or any failure history. I just bought the car and noticed that the air filter housing had been destroyed by a backfire. If I had seen it and the dirt in the intake before I bought, I would have passed. The car only had 40,000 miles on it but they were sure rough miles. I did a service history on the car and sure enough, one spark plug wire was replaced under warranty (did not say which one). I also noticed that the number one spark plug wire was wearing on a coolant hose clamp but had not worn through yet. I have 4 Bi-fuel Cavaliers and every time I get one plugs and wires are changed. Still curious about the GM service policy letter and the two blowoff valves on the air cleaner cover. This is the first car I have seen with them.

[kirkbenge]

Re: Backfire

I had the same problem in my '01 cavalier. I would get occasional backfires on acceleration, but ONLY in CNG mode, never while running on gasoline. It even blew out my air filter housing. But when I changed my plugs and wires, the problem went away.
So I agree with soarhead25, CHECK YOUR PLUGS AND WIRES.


I still get an occasional backfire though while cranking at ignition. If I have to crank for more than three of four seconds, then I might occasionally get a mild backfire. Anyone experienced this? Any logical explanation?

[clean03]

Re: Backfire

I had the same problem in my '01 cavalier. I would get occasional backfires on acceleration, but ONLY in CNG mode, never while running on gasoline. It even blew out my air filter housing. But when I changed my plugs and wires, the problem went away.
So I agree with soarhead25, CHECK YOUR PLUGS AND WIRES.


I still get an occasional backfire though while cranking at ignition. If I have to crank for more than three of four seconds, then I might occasionally get a mild backfire. Anyone experienced this? Any logical explanation?

Keep your foot off the accelerator pedal while cranking and you shouldn't backfire while cranking.

[kirkbenge]

Re: Backfire

That sounds reasonable, but I never have my foot on the accelerator while cranking... maybe I ought to start trying that, maybe giving it some gas while starting would make it go away.

[implanenuts]

Re: Backfire

I get the mild backfire on start sometimes, then it will crank and crank before it starts. I found that if it does not start right up first try then I put the pedal to the floor and crank then it starts right up.

[siai47]

Re: Backfire

I just want to bring this backfire thing up one more time. Since I first posted this, I am begining to think this is move prevalant then I thought. My friends grandmother was driving her Cavalier and caused a backfire when she tried to start it with her foot on the gas. An inspection of the air cleaner cover, filter and box showed no problems however the explosion really frightened her. I also purchased some used bi-fuel parts on E-bay. One of the parts was the gas distribution assembly (goes between the throttle body and the air cleaner). This assembly was packed with dirt---just like the used Cavalier that I bought with the broken air cleaner. The point is, if you have a backfire, it is very important that you check the air cleaner for cracks. Even if not cracked you should remove the cover and be sure that the filter has not been pushed out of position and into the airbox. Either condition will allow unfiltered air into the engine shortening its life. The airbox and cover are standard Cavalier and easy to get at any junkyard.

[bufordthelittle]

Re: Backfire

I had the backfire problem a month after buying my 02 Cav. The dealer said that the problem was the GMS and quoted around $2700 to replace it. I didn't have the money at the time and that was almost half of what I paid for the car so I decided to take the CNG fuse out and run it on gasoline. After months of this and only getting 26 mpg I took it into a garage to give it a tune up to see if I could save some at the gasoline pump. They remarked that one of the spark plug wires had corroded (because it wasn't installed with grease) and pulled apart when they went to check the spark plug. They ended up replacing the spark plugs and wires. After that it was running at about 30 mpg. I decided that my car probably had the same one cylinder not firing problem listed in this thread, so after taking the GSM apart not finding any visual problems to either of its circuit boards, I put the CNG fuse back in. I've ran the car on CNG for 2 commutes haven't had a backfire yet. I'm glad that the dealer with the CNG certified mechanic picked up on that one! Hopefully, I'll continue to run error free.

I also had the air filter cover broken up due to the backfires. Originally, the dealer quoted $120 for a replacement so I found a non-release valve one at the local junkyard for $10. I had seriously contemplated having the dealer replace the GMS a few weeks ago because of the rising gasoline prices. When I called back in, they said that the air filter cover would be covered under the Chevy 100k warranty. If you have a broken cover, press the dealer for this option.

[kirkbenge]

Re: Backfire

Thanks for the info Bufordthelittle.

I think it is obvious that this backfire issue is a fairly common problem, and not just for Cavaliers. A few weeks ago my brother phoned me to ask what I thought he should do for his Chevy K2500 Pickup truck. It had been backfiring quite severely, especially on acceleration. I told him about my experience, and after changing the plugs and wires, the problem was cured. (When changing his wires he found that one was severely corroded, he also discovered that his filter housing was damaged by the backfires).

[shanghaiguy]

Re: Backfire

Perhaps you might be able to answer my backfire question as it seems you pointed out two diffrent kinds of backfire. I have an aspirated expedition, and the backfire usually occurs after I declerate (usually allowing the engine to brake for me; like approaching a stop light). Then when I accelerate from the stoplight, i'll get the backfire. Most of my backfires will stall the vehicle, but the most recent one caused to motor to run very rough. i took it to my favorite mechanic and he said that some "vacuum hoses" had popped off. Is this a lean condition or a rich condition?

[paradisequest]

Re: Backfire

My 2000 Cavalier would backfire when the air temperature was below freezing and I was just starting the car or if I tried to accelerate while it was still cold. I ruined 2 different air filter covers.

I changed the plugs and wires and that seemed to eliminate the problem. I also put 4 long bolts through the air filter cover and placed 4 springs on the bolts. This holds the air filter down with the spring tension. If it does backfire the air filter cover will release with the springs.

I also replaced the air filter with a KNR filter that has less resistance.

I had heard that the smell additive to the CNG will foul the plugs and cause the backfiring over time. Not sure if this is why, but changing the plugs and wires helped. It hasn't backfired since, but I will know for sure this winter.

[bufordthelittle]

Re: Backfire

My 98 Cav had an intermittent backfire condition that was worse on heavy accell. The biggest backfire blew up the air filter box!

As AFV Tech pointed out, a backfire in the intake side of the engine typically indictates a lean fuel mixture engine condition, and a backfire in the exhaust system would typically indicate a rich fuel mixture engine condition.

Now my backfire was only present while running on CNG, and not gasoline, which was pointing me to check my cng fuel system. (Filters and such)
However, after reading the backfire symptom chart in the GM Cavalier repair manual, it states that since CNG is a gaseous fuel, it requires much more KV to jump the spark plug gap and ignite the cng/air mixture. After removing the spark plugs I had found a light carbon track on #1 spark plug that was causing the misfire. I replaced them with generic autolites and have not had a problem with them yet, although I really like to replace plugs with oem.
Check your spark plugs and wires!

I also came across a GM bulletin for #4 spark plug wire going bad, but didn't research the bulletin to see why as of yet.

I had a similar backfire problem but a tune up with new spark plugs and wires seems to have fixed the problem. Turns out the previous owner had replaced the spark plug wires but didn't use the dielectric grease. When the shop when to check the plugs the wire just came apart. I suspect there was some corrosion in between the plug and the wire contact. Thanks for passing the info along. I suspect that there still may be something wrong with the CNG system on my cav because it will sometimes make a high pitch whining noise when operating. You made mention of the "backfire symptom chart in the GM Cavalier repair manual". Where can I get a hold of this GM Cavalier repair manual?

Thanks

[wacbass]

Re: Backfire

I am having a backfire issue only when the RPM's are over 5000. For example, when driving up a hill and having to pass a vehicle, I step on the gas and the car kicks down into a lower gear and then feels as if it is bogging down and is very loud and shakey. The 5000 or above RPM is only reached when I have to step on the gas around 50 MPH to 65 MPH. I have blown 2 air filter covers and replaced the plugs inbetween blowing the last cover. I didn't replace the wires because they looked almost new. Has anyone experienced something similar or can anyone explain why I can't run on CNG at or above 5000 RPM? I let the CNG run out and tried the same thing on gasoline and the car would really bog down and shake a little at that high RPM but no backfire.

Thanks in advance.