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Old 02-18-2013, 11:51 PM   #1
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Backfires when cold

My 07 GT makes this popping exhaust noise, like backfires when I rev it while is cold. It also does it when warm, but not as much. Does anyone ever had this problem. If so, what could be causing it? Any help I get is appreaciated.
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Old 02-18-2013, 11:57 PM   #2
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My 07 GT makes this popping exhaust noise, like backfires when I rev it while is cold. It also does it when warm, but not as much. Does anyone ever had this problem. If so, what could be causing it? Any help I get is appreaciated.
Could be an exhaust leak. Have you recently messed the exhaust? If not check all connections or a hole in a pipe or muffler. Is it throwing any CEL codes?
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Old 02-19-2013, 12:09 AM   #3
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No codes at all. I'll check the mufflers. I bought the car used with 47K on it. I also heard it could be bad gas, bad spark plug, or a bad coil.
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Old 02-19-2013, 04:36 AM   #4
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Quote:
Originally Posted by tonyjuan View Post
My 07 GT makes this popping exhaust noise, like backfires when I rev it while is cold. It also does it when warm, but not as much. Does anyone ever had this problem. If so, what could be causing it? Any help I get is appreaciated.
First, I too have an 07 w/manual trans. My pony does the same as yours. It isn't exactly a problem. It's... Better yet, l will paraphrase someone.


Deceleration Backfire is caused by fuel burning in the exhaust manifold or header.

No ifs ands or buts, that’s what causes it. But the bigger question is how does gas get there in the first place, and that’s a bit more complicated. Generally, there are a variety of ways it gets there, and a variety of things that can make the backfiring worse. But there’s a kicker, and something you should understand before we go any farther:

A motor in perfect tune will exhibit deceleration backfiring.

Therefore, just because your motor is banging it up, doesn’t mean there’s anything wrong. And consequently:

Getting rid of the noise means de-tuning your motor.

Yup. If you’ve jut got to eliminate that popping, you’ll have to accept the fact that your motor is going to be forced to run rich to do it, and that isn’t necessarily a good thing.

Ok, so you’re driving along at some given rpm, and suddenly you decide to decelerate, and you reduce the amount of throttle. This causes an “overrun” – that is, the motors rpm is turning faster than the fuel provided can support, so the motor begins to spool down. This causes a couple of things to happen.

First, when you close the throttle, you are also closing the throttle plate. This reduces the air and fuel flowing into the motor, and increases the vacuum (lowers the pressure). This results in less air and fuel in the cylinder during the power stroke, which in turn results in a lower pressure in the combustion chamber. The A/F mix burns faster in proportion to the pressure applied? Well, when we reduce pressure this way, the mix burns slower. This results in two things happening.

1. The lower burning fuel generates less heat, and the cooling effect of the non-burning fuel tends to “quench” the flame front, or slow it down even further. Because the mix is burning much slower, the exhaust valve can open before all the fuel is consumed, and the unburnt fuel is ejected into the exhaust.

2. The engine designers, in order to promote smoother idling and better combustion, ****** the spark when the throttle is shut, and this results in the mix being lit later.

So, now we end up with unburnt fuel in the exhaust, and burning fuel being ejected into the exhaust, and bang! Backfire.

So the bottom line, is: That backfiring is perfectly normal and expected. If you’ve just got get rid of it, that’s up to you. You’re entitled to set your motor up the way you want, and your goals are your goals. But don’t refer to it as “fixing” the popping. Rather, the correct way to think of it is “de-tuning a bit to get rid of the popping”.

I hope this helped




You will get worse gas mileage by getting rid of it because you will have to run richer on decel inorder to raise the chamber pressure engough to burn all the fuel.
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Old 02-19-2013, 05:22 AM   #5
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I wouldn't rev your car to much or too high while its cold.
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Old 02-19-2013, 11:34 AM   #6
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I wouldn't rev your car to much or too high while its cold.


I make sure I get to the track hours early to run my car from a dead cold hehe.
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Old 02-19-2013, 01:34 PM   #7
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Thumbs up backfire

That's really helpful. I will leave it alone and enjoy the car.
Thanks a lot.
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Old 02-19-2013, 04:12 PM   #8
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Mine does the same thing when it's cold. I notice if I start driving before I let it warm up and the rpm's are high as soon as I let off the gas ill get a backfire. Once it's warm it runs like a champ!
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