Deceleration Popping
Thread Starter
Instructor
Joined: Mar 2006
Posts: 178
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Deceleration Popping
Why the popping on deceleration. Blackwing, Granatelli mas. WCC air bridge and coupler. American Racing headers,cats and crossover. Corsa Indy muff's. 2004 C5 6 speed bought new. It's been custom tuned. Stock engine.
Thanx
Thanx
Burning Brakes
Joined: Feb 2005
Posts: 1,190
Likes: 0
From: Fayetteville AR
I believe its from air rushes back into the pipe after the exhaust flow from each cylinder is expelled and then this air mixes with un-burnt fuel caused by a rich condition and detonates inside of the exhaust. If its minor it is OK but if its real bad and it's actual backfire (fresh air is getting into the exhaust further up the pipe) then its bad. Check for air leaks around the exhaust systems and double check the donuts, check all torques on eveything. Read this link it may help you.
http://forums.corvetteforum.com/showthread.php?t=373824
http://forums.corvetteforum.com/showthread.php?t=373824
Melting Slicks
Joined: Jul 2004
Posts: 2,340
Likes: 35
From: Folsom Lake CA
During a road tune tweak for drivability I had done the other day after a previous dyno tune, I mentioned to the tuner that I didn't like the way the car behaved when shifting. I can't put it into words well, but in a stick, these cars have a weird feel that's especially noticable when shifting from 1st to 2nd with a stock tune. It's almost as if you can't get a smooth upshift, and you have to let the clutch out slower than you would normally let out a clutch in any other type of car. And, it seemed like you had to give more gas than necessary when letting the clutch out to prevent the car from jerking. But, often this process resulted in you slipping the clutch a little longer than necessary, and you had a jerk anyway! 
And, just when you think you have the process down for this car, it acts differently the next time you try upshifting, and the same process results in "hesitant" shifting. It's almost as if no matter what you do, you can never get a smooth upshift. See, I told you it was weird and I couldn't explain it. It really started to bother me, and made me more mad at myself for not getting an A4 like I originally wanted. Yes, I've driven other C5s with sticks and they were all the same. This NEVER happened in the C4s (and I previously had a C4 with a stick), so I actually thought it was something to do with the clutch, or was a by-product of the tranny-in-the-rear design, but later surmised that it HAD to be something with the tune, which is why I mentioned it to the tuner.
The tuner seemed to know EXACLTY what I was talking about, and showed me a table that related to the timing being retarded (pun intended) upon pressing the clutch in to shift. "Why the he|| would you want to have your timing retarded when upshifting?", I asked. He said he thought it might have been done that way for emissions testing at the factory level, which makes sense to me. After all, manufacturers have to pass much more stringent tests than we do when we get our cars smog-tested for registrations.
Anyway, the tuner adjusted the timing upward to match what it was before shifting, and not only is the car more pleasant to shift, the deceleration popping disappeared as a by-product. I also had some popping when putting the clutch in to shift (even upshifting), and that popping is gone, too. Granted, I only have a "CAI", x-pipe and cat-back, but it might be food for thought for you and your tuner.
FWIW, EVERYONE says popping is natural, especially with a cat-back exhaust, but now I know better. Apparently, it's only natural if you don't know all the tricks with tuning.
And, just when you think you have the process down for this car, it acts differently the next time you try upshifting, and the same process results in "hesitant" shifting. It's almost as if no matter what you do, you can never get a smooth upshift. See, I told you it was weird and I couldn't explain it. It really started to bother me, and made me more mad at myself for not getting an A4 like I originally wanted. Yes, I've driven other C5s with sticks and they were all the same. This NEVER happened in the C4s (and I previously had a C4 with a stick), so I actually thought it was something to do with the clutch, or was a by-product of the tranny-in-the-rear design, but later surmised that it HAD to be something with the tune, which is why I mentioned it to the tuner.
The tuner seemed to know EXACLTY what I was talking about, and showed me a table that related to the timing being retarded (pun intended) upon pressing the clutch in to shift. "Why the he|| would you want to have your timing retarded when upshifting?", I asked. He said he thought it might have been done that way for emissions testing at the factory level, which makes sense to me. After all, manufacturers have to pass much more stringent tests than we do when we get our cars smog-tested for registrations.
Anyway, the tuner adjusted the timing upward to match what it was before shifting, and not only is the car more pleasant to shift, the deceleration popping disappeared as a by-product. I also had some popping when putting the clutch in to shift (even upshifting), and that popping is gone, too. Granted, I only have a "CAI", x-pipe and cat-back, but it might be food for thought for you and your tuner.
FWIW, EVERYONE says popping is natural, especially with a cat-back exhaust, but now I know better. Apparently, it's only natural if you don't know all the tricks with tuning.
Last edited by MrLeadFoot; Mar 14, 2006 at 06:08 PM.
Drifting
Joined: Feb 1999
Posts: 1,481
Likes: 1
From: San Diego CA
One other thing to consider is your exhaust system. When you're off the throttle, gas flow is reduced and the Corsa RSC muffler design loses much of it's noise canceling effect.
Personaly, I love it. I've gotten used to the motorboat idle which I can take or leave but under deceleration, my Corvette sounds better then my open exhaust race car!
Mike
Personaly, I love it. I've gotten used to the motorboat idle which I can take or leave but under deceleration, my Corvette sounds better then my open exhaust race car!
Mike
Melting Slicks
Joined: Feb 2001
Posts: 2,791
Likes: 355
From: Northville, MI
Originally Posted by MrLeadFoot
FWIW, EVERYONE says popping is natural, especially with a cat-back exhaust, but now I know better. Apparently, it's only natural if you don't know all the tricks with tuning.
Collections Hold
Joined: Aug 2002
Posts: 2,899
Likes: 6
From: Fort Wayne Indiana
Originally Posted by MrLeadFoot
During a road tune tweak for drivability I had done the other day after a previous dyno tune, I mentioned to the tuner that I didn't like the way the car behaved when shifting. I can't put it into words well, but in a stick, these cars have a weird feel that's especially noticable when shifting from 1st to 2nd with a stock tune. It's almost as if you can't get a smooth upshift, and you have to let the clutch out slower than you would normally let out a clutch in any other type of car. And, it seemed like you had to give more gas than necessary when letting the clutch out to prevent the car from jerking. But, often this process resulted in you slipping the clutch a little longer than necessary, and you had a jerk anyway!
And, just when you think you have the process down for this car, it acts differently the next time you try upshifting, and the same process results in "hesitant" shifting. It's almost as if no matter what you do, you can never get a smooth upshift. See, I told you it was weird and I couldn't explain it. It really started to bother me, and made me more mad at myself for not getting an A4 like I originally wanted. Yes, I've driven other C5s with sticks and they were all the same. This NEVER happened in the C4s (and I previously had a C4 with a stick), so I actually thought it was something to do with the clutch, or was a by-product of the tranny-in-the-rear design, but later surmised that it HAD to be something with the tune, which is why I mentioned it to the tuner.
The tuner seemed to know EXACLTY what I was talking about, and showed me a table that related to the timing being retarded (pun intended) upon pressing the clutch in to shift. "Why the he|| would you want to have your timing retarded when upshifting?", I asked. He said he thought it might have been done that way for emissions testing at the factory level, which makes sense to me. After all, manufacturers have to pass much more stringent tests than we do when we get our cars smog-tested for registrations.
Anyway, the tuner adjusted the timing upward to match what it was before shifting, and not only is the car more pleasant to shift, the deceleration popping disappeared as a by-product. I also had some popping when putting the clutch in to shift (even upshifting), and that popping is gone, too. Granted, I only have a "CAI", x-pipe and cat-back, but it might be food for thought for you and your tuner.
FWIW, EVERYONE says popping is natural, especially with a cat-back exhaust, but now I know better. Apparently, it's only natural if you don't know all the tricks with tuning.
And, just when you think you have the process down for this car, it acts differently the next time you try upshifting, and the same process results in "hesitant" shifting. It's almost as if no matter what you do, you can never get a smooth upshift. See, I told you it was weird and I couldn't explain it. It really started to bother me, and made me more mad at myself for not getting an A4 like I originally wanted. Yes, I've driven other C5s with sticks and they were all the same. This NEVER happened in the C4s (and I previously had a C4 with a stick), so I actually thought it was something to do with the clutch, or was a by-product of the tranny-in-the-rear design, but later surmised that it HAD to be something with the tune, which is why I mentioned it to the tuner.
The tuner seemed to know EXACLTY what I was talking about, and showed me a table that related to the timing being retarded (pun intended) upon pressing the clutch in to shift. "Why the he|| would you want to have your timing retarded when upshifting?", I asked. He said he thought it might have been done that way for emissions testing at the factory level, which makes sense to me. After all, manufacturers have to pass much more stringent tests than we do when we get our cars smog-tested for registrations.
Anyway, the tuner adjusted the timing upward to match what it was before shifting, and not only is the car more pleasant to shift, the deceleration popping disappeared as a by-product. I also had some popping when putting the clutch in to shift (even upshifting), and that popping is gone, too. Granted, I only have a "CAI", x-pipe and cat-back, but it might be food for thought for you and your tuner.
FWIW, EVERYONE says popping is natural, especially with a cat-back exhaust, but now I know better. Apparently, it's only natural if you don't know all the tricks with tuning.
He's talking about DFCO Spark & you're correct, it does need to be altered to decrease the condition spoken about above. Also, decel fueling needs to be accurate as well..
Last edited by DTE Powertrain; Mar 15, 2006 at 07:02 PM.
