after installing the hks exhaust and downpipe, my car start to making some poping noise during shift, more so when it cold. sometime at idle too. is this normal with that exhaust? my car is bone stock, only mods are hks turbo timer, hks downpipe and hks exhaust.

 

Yes, doing a search for "backfire" or "backfiring" would have brought you the answer. However, after removing the pre-cat, you will notice some backfiring.

 

so it's normal to have some back fire with my setup. is there a way correct the backfiring?

 

Could be your spark plugs. Have you replaced within the last 15K miles? Also could be running a tad rich and some of the leftover gas could be igniting in the wrong places causing a backfire.

 

The plugs are new, the car always ran rich, i was having hard time passing smog couple day ago, but after switching out a set of new 02 it passed fine. maybe i though it's normal with the mods i have?

 

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