the exhaust does sound very nice, but you lose power putting it on.

the other day i saw a guy in his s2k, he had a nice dual exhaust with his silencer's on.... it looked like each muffler had about a half inch or air flow.

its not about sound anymore... its about the quality of how your motor is running. Well.. except if its TOO LOUD LOL!!

 

lets see what the plugs look like man. If its colder outside you would run a little leaner

 

No, the cold makes your car run leaner. Check maint things first like plugs, make sure not fouled and gap is 0.30-0.33 if your still running factory gap. Verify air cleaner is clean—though with a solid non overly rich tune on a clean filter this shouldn’t really cause this. Do you run a wide band to monitor your afr?

Sometimes you can have the same backfiring symptoms if your running overly lean too, looking at your plugs will tell you. Post some pics if you need to and I will tell you how they look.

 

What set up/hp are you running?

 

What ECU are you running? AEM? If so, your DFCO (Decel Fuel Cut) might not be kicking in, therefore allowing a small amount of fuel to still be injected into the engine. Or, even if it is, there is a thing called injector dead time. This is the time it takes for your injector to respond to an "open-sesame" command from the ECU. It gets complicated because this time varies with the voltage at the battery. The ECU has a lookup table of dead-time vs. battery voltage and really is the main reason the ECU looks at battery voltage in the first place (there are other less important reasons). This time can range from 0.65ms to 2.1ms. So if the injector dead time is off, then you're injectors are still going to be opening (allowing gas to injected) at the wrong time, hence the backfiring.

 

hmm very interesting. I know at one point a while ago one of my injectors was staying open for some reason, but then it went away and worked normally.

 

That could do it

 

just did a couple pulls in my low boost and no issue at all. It sounds like it may be my boost spiking and the boost cut kicking in