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So, as the thread title states… Ever since I’ve had my car, I’ve had an issue with a “backfire” when I’m hard on the accelerator and letting off to shift between gears. It seems to be worse between 1 to 2 and 2 to 3, but almost non-exhistant after 3rd gear under heavy acceleration and only seems to be really bad if I’ve been idling for awhile in traffic. Guess I shouldn’t call it a backfire…it’s more like a very loud pop. I’ve always attributed it to my exhaust, but now that I have a new OEM cat, it seems to be worse. This is why I’ve tried to find the tuner/previous owner. I obviously don’t want to do any damage to the car……would this be normal? Would it be something to be concerned about?
 

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This normal and desired by many with an aftermarket exhaust.

Sent from AutoGuide.com App
 

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In my experience when you get a backfire its due to collection of unburned gasses in the exhaust system that detonate.

With the direct injection engine on these cars, a number of unique things are going on at the same time.

The ECM uses the fuel mixture to product HP, but it also controlls head temperature to a certain extent with mixture. So it may and will increase the fuel ratio under circumstances other than just to product HP. As a result, there may be more hydrocarbons entering the exhaust under different conditions that can contribute to this.

Also, the ECM is continuously "learning". When in cruise for a while, the ECM will adjust the trims for maximum mileage. If you hammer it hard after one of these periods, the first few seconds may result in pinging and kind of a strangling sensation as the ECM "learns" that the operator is asking for max HP now and paramaters are reset. Its possible that when you go to a max performance takeoff following an extended idle period that you are experiencing the results of this kind of transition from high MPG to high HP.

The one thing that you DO NOT want to hear is pinging. Other sounds may be irritating but will not result in high dollar issues. Pinging is death on these motors and not to be sustained for very long.
 

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Nope.....no pinging. Just the backfire. The car does seem to "load up" as well when sitting idle. But like I said once before, a good blip of the throttle to 3k and it cleans it out and it idles better.
 

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Listen to any race car going through the gears. You will hear all sorts of bobs and bangs. If your exhaust is pretty open, that is what you are hearing. And it is much more prominent shifting between lower gears.
 

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I get some nice 'pops' from my stock exhaust when practicing the NLS.

Don't sweat it, not an issue.
 

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So, as the thread title states… Ever since I’ve had my car, I’ve had an issue with a “backfire” when I’m hard on the accelerator and letting off to shift between gears. It seems to be worse between 1 to 2 and 2 to 3, but almost non-exhistant after 3rd gear under heavy acceleration and only seems to be really bad if I’ve been idling for awhile in traffic. Guess I shouldn’t call it a backfire…it’s more like a very loud pop. I’ve always attributed it to my exhaust, but now that I have a new OEM cat, it seems to be worse. This is why I’ve tried to find the tuner/previous owner. I obviously don’t want to do any damage to the car……would this be normal? Would it be something to be concerned about?
I would suggest that you take the vehicle to a GM dealer. A diagnosis is an important part in determining the cause of the noise and nature of the concern. It also helps to determine the estimated cost of repairs. Once a proper diagnosis has been conducted by a GM dealership you can decide how you want to proceed. I would be happy to find a GM dealer in your area that services Pontiac vehicles. Please send me a private message if you would like for me to do this.

Jackie
GM Customer Care
 

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is it kinda like this...towards end of the first video and the start of the second....
 

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You have a small exhaust leak, check all the clamps on the exhaust and or readjust them, had the problem fixed it. It can be just a pin hole but most likely a loose clamp.
 

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You have a small exhaust leak, check all the clamps on the exhaust and or readjust them, had the problem fixed it. It can be just a pin hole but most likely a loose clamp.
This was going to my suggestion also, but sense you said it was loading up at idle, then it is more likely from the un-burnt gases mention in above post..Should be one or the other or maybe even both.. Not good in either case, bad on valves and your muffler system and turbo.
 
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