Exhaust Pops/afterfire on decel

08Bullitt_0067

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As the title states, I get a somewhat frequent exhaust pop or afterfire when i lift off the throttle with the car in gear. It sometimes sounds like a fire cracker or a loud snap. If I pull it out of gear right away, no noises. Mods listed below. This started happening after swapping a new motor and adding the blower with dyno tune. If this is tune related, can it be eliminated? Any other ideas?

2008 with 4.6
Mods:
Whipple HO
comp 127500 cams
Mac LTs
Mac O/R pro-chamber
Corsa extreme axle backs
 

travelers

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It's tune and mod related. Mine does it also and not sure if it can be eliminated or at least slowed somewhat
 

stkjock

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Common and normal IMO

It’s mod and tune related, it’s unburned fuel hitting the hit exhaust
 

07 Boss

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I know when my car starts to pop excessively it is time to change my plugs. When I ran HT0 plugs it used to pop and gurgle all the time. When I switched to brisk plugs the popping all but went away. Now when I start to hear her pop I throw a new set of plugs in there and she becomes quiet again. Can't explain why except conjecture it has something to do with the stirrup style strap as opposed to the conventional spark plug design. It is my belief that the strap shrouds the spark and prevents good combustion under decel conditions and more unburnt fuel makes it's way into the exhaust. Back in the day when we had hard to ignite fuel mixtures we would sometimes side gap our plugs to get more complete combustion and a faster burn by exposing the spark directly to the air fuel mix.
 

Iceman62

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IMO...get a tuner & tune files configured f/your mods. A good shop can adjust AFR to reduce your issues, or even cease all-together. Worth a try...why dump all that ca$h into your ride and not invest another $500 to make it run correct...??
 

BEAR

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Do a simple check around the headers & upstream pipe connections for any leakage. A leak will suck in fresh air on high vacuum conditions & make gunshot like sounds when it fires unburned gas
 

travelers

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I know when my car starts to pop excessively it is time to change my plugs. When I ran HT0 plugs it used to pop and gurgle all the time. When I switched to brisk plugs the popping all but went away. Now when I start to hear her pop I throw a new set of plugs in there and she becomes quiet again. Can't explain why except conjecture it has something to do with the stirrup style strap as opposed to the conventional spark plug design. It is my belief that the strap shrouds the spark and prevents good combustion under decel conditions and more unburnt fuel makes it's way into the exhaust. Back in the day when we had hard to ignite fuel mixtures we would sometimes side gap our plugs to get more complete combustion and a faster burn by exposing the spark directly to the air fuel mix.

l think in the old day that's call indexing the plugs.
 

fdjizm

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Isn't the "burble tune" all the rage now? you want gunshots when you decelerate.
All the cool kids are doing it.
 

05stroker

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I've always used HTOs and never had this issue. I would be hunting a exhaust leak if it was mine.

If it's tune related, get Lito in your life.
 

tjm73

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These kinds of things always sound like a fueling issue to me. ie.. too much fuel on the deceleration throttle position tuning. But I am not a tuner, so I am really just guessing.
 

1950StangJump$

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One person's "normal" is another's "problem." But, it is fair to say that it is very "common," especially with aftermarket tunes and open exhausts. While you might be able to tune it out, or tune it down, I don't think it is indicative of an issue.

I have two separate tunes . . . one dyno and one remote data logged. One pops more than the other, but they both do it. But, the tone, amount, and volume differs between the two. So, I think the sounds are a combination of tune and exhaust . . . I have headers, high flow cats, and the "flow through" type mufflers.

Years ago, I had a brand new Camaro SS with the two tone exhaust. Basically, a valve opened up after 3500 RPMs and make it loud like you have no mufflers. Well, if you pulled the fuse, the valve stayed open all the time. Guess what? It also made the car gurgle and pop on decel (with zero other mods) because the valve was now open on decel when it had been closed. Point being, the standard exhaust drowns out a bunch of the pops and gurgles you might be hearing down with the headers and catless exhaust.
 

dark steed

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One person's "normal" is another's "problem." But, it is fair to say that it is very "common," especially with aftermarket tunes and open exhausts. While you might be able to tune it out, or tune it down, I don't think it is indicative of an issue.

I have two separate tunes . . . one dyno and one remote data logged. One pops more than the other, but they both do it. But, the tone, amount, and volume differs between the two. So, I think the sounds are a combination of tune and exhaust . . . I have headers, high flow cats, and the "flow through" type mufflers.

Years ago, I had a brand new Camaro SS with the two tone exhaust. Basically, a valve opened up after 3500 RPMs and make it loud like you have no mufflers. Well, if you pulled the fuse, the valve stayed open all the time. Guess what? It also made the car gurgle and pop on decel (with zero other mods) because the valve was now open on decel when it had been closed. Point being, the standard exhaust drowns out a bunch of the pops and gurgles you might be hearing down with the headers and catless exhaust.
This ^^^^^
When I had muffler deletes with stock H and cats, it burbled and popped on decel, especially cold.
FRPP GTA mufflers now and it’s all but gone. It did it on stock tune and Bama tune (before AM bought them)


Sent from my iPhone using Tapatalk
 

08Bullitt_0067

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OK, so it's not the what i consider normal burble and light popping when decel in gear, I do have that too and it did that before the blower/new tune. What i am hearing sounds like an ignition bang. Sometimes it sounds what people would call a 'backfire', but mostly it's like firecrackers or gunshots.

Long story short, when i blew my stock motor last year, it blew a bunch of oil into the exhaust. The shop i had it at drilled a hole in each muffler to drain the oil and I had forgotten about it. I just had the holes welded in and the really annoying popping noise i would hear that sounded like metal 'slapping' seems to be gone now. so i still have the firecracker/gunshot noise if i get on it and lift off the throttle still in gear, but not as bad as before.

So some say it's somewhat 'normal' for my mods and others say the tune needs adjustment. But I think the consensus is that some extra fuel is being sent into the exhaust and igniting there. With the holes in the muffler welded up, I think it's more bearable now. I just hope that there are some flames coming out of the tails when it does happen haha.

I appreciate all the input.
 

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