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What causes the popping / backfire

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39K views 46 replies 20 participants last post by  lukerihl  
#1 ·
Ok so I just got home from a weekend vacation with a few of my friends. We decided to take my friends SRT-4, and wow, we had alot of fun with the car on the way there. It seems like the snapping and popping on deceleration just doesn't get old.

Now I'm a 2008 Mitsubishi Evo X owner, so I know my way around a car. Now If I ran a straight pipe on my Evo, it would sounds obnoxious and not crackle or pop or any of that cool SRT-4 Stuff.

I just want to know what is causing the pops. Now i understand that the pops are coming from unburnt fuel igniting in your exhaust but, why do you have so much extra fuel especially for a good amount of time even after u let off the accelerator.

Do your injectors stay on at a very low duty cycle when your throttle plate is completely shut? That would be my only guess. I would really like to find out why and know if you can change the maps on other cars such as my own through our evo tuning software, to act like the srt-4 on deceleration.

I know this has probably been covered numerous times on the forums but I really can't seem to find a solid answer.
 
#2 ·
From my understanding, our cars are tuned from the factory to pop and crack like this. Its from the injectors firing on deceleration. As sick as it sounds, there are some SRT guys who have had their tuners eliminate it from their tunes.
 
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#24 ·
The injectors do not fire during decaccel unless your are below 30MPH. Below 30MPH this fuel is used to keep a smooth transition back to throttle and keep the engine braking down while city driving. At least this is how it was explained to me when I asked about it when I was looking at getting my car tuned.
 
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#9 ·
PVO gremlins !!
 
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#13 ·
I've been actually considering one of those, for those days I fell like I wanna be loud, and putting something a little more quiet for everyday. I do a lot of highway and 75 mph at like 2800rpms is super loud, family doesn't tend to like riding with me cuz they can't have a conversation in the back seat lmao
 
#31 ·
Ok so I just got home from a weekend vacation with a few of my friends. We decided to take my friends SRT-4, and wow, we had alot of fun with the car on the way there. It seems like the snapping and popping on deceleration just doesn't get old.

Now I'm a 2008 Mitsubishi Evo X owner, so I know my way around a car. Now If I ran a straight pipe on my Evo, it would sounds obnoxious and not crackle or pop or any of that cool SRT-4 Stuff.

I just want to know what is causing the pops. Now i understand that the pops are coming from unburnt fuel igniting in your exhaust but, why do you have so much extra fuel especially for a good amount of time even after u let off the accelerator.

Do your injectors stay on at a very low duty cycle when your throttle plate is completely shut? That would be my only guess. I would really like to find out why and know if you can change the maps on other cars such as my own through our evo tuning software, to act like the srt-4 on deceleration.

I know this has probably been covered numerous times on the forums but I really can't seem to find a solid answer.
Do you go clockwise or counter-clockwise?
 
#33 ·
Haha, it's so funny around me when all the Japanese cars are getting tuned for this. I listen and hear an RSX-S popping all over the place and I'm like wtf? I know they love our cars, but trying to be like ours with their riced out shiiiieeet ...is just pathetic. lol. Watch out for the tow hooks they be sporting these days! :D
 
#34 ·
try a full 3" catless exhaust with resonator removed...get a few nice pops and crackles on decel, as well as a decent amount of flames on shifting at redline :p
 
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#36 ·
With stage 1 there is a slight increase in pops and tone of the exhaust. The more you drive your car and pay attention to it, the more youll notice it with stage 1. Otherwise im sure alot of people that dont pay attention dont notice much.
 
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