Ever since I but in my SLP Axle-backs, my car backfires when it is cold (only). If I rev the engine I hear a pop out of the exhaust. After a minute or so it does not do it anymore. What causes this? I read somewhere it is the plugs mis-firing. 16,000 miles on my 08 GT.

 

its normal for slp. why? i do not know. but mine did the same thing.

 

Yeah, thats what I am reading on other forums. I just wanted to make sure there wasnt a problem. Thanks

 

These car will backfire with stock exhaust too if you don't let them warm up in the winter.

When I start my car after its been sitting all night and the temps are below freezing the car jumps to 1600-1800rpm at idle for about 15-20seconds depending on how cold it is. I usually let it warm up until the rpm drop to the sub 850rpm range (I keep a dash hawk connected that's how I can tell real rpm). Then its safe to pull out and drive without sounding like a model T.

 

+1 ^ You need to let it warm up until the rpms drop below 1k and hold. Also I would try not to rev it up until its warm. Mine has back fired a few times if I dont let her warm up.

Not sure what happens to produce the backfire.

 

Cars backfire when they are warming because they are running rich to allow the engine to warm up. Most cars do this it's just more noticeable when you swap out exhaust pipes.

 

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the backfire happens when the raw fuel gets out into the exhaust, the cats ignite the fuel and can actually be very harmful for your cats as it can clog them up. Point is simple, let the car warm up properly, you don't have to wait until the temp needle climbs up. All you have to wait for is the rpm drop below 1000 like mentioned before, or as I prefer 850.

 

Oh, well same difference.

 

On startup with my new tune, it goes immediately to under 1k rpm now, not like before.

 

The fuel is getting past the cold cats while the engine
is running rich while the PCM is in open loop mode waiting
for the cats to get up to operating temps to go into
closed loop fuel mode.
Its normal and happens with the stock exhaust system
as well. Its just not as noticable.