I am having an exhaust leak from the driver side header which is progressively getting worse. I ordered the fel-pro gasket and plan on replacing it in the next few days. I started getting a consistent popping from the back after i accelerate and then let off. It happens more at higher RPMs while letting off the throttle. Is this because of the header gasket?

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Most likely that is your problem, exhaust leaks ahead of the O2 sensors can cause the sensors to read a lean condition which the computer will try to compensate for. The subsequent "rich" A/F can cause plugs to foul and create a missfire condition, and any unburned fuel will ignight in the exhaust. If you've still got a cat the messed up A/F ratio can ruin it too. Basically, header gasket leaks can be a EFI cars worst enemy.
I'm running copper gaskets but also use the suplied SLP "single" gasket for extra crush and better seal on the center two pipes because the coppers don't seal well right in the middle where there is no bolt. I'm also using the 1" long Stage 8 locking header bolts and haven't had to touch them since I installed them.

 

When I first did the motor I was using the SLP installation kit. I never had a problem with those gaskets. Since I have redone it I just went with the cheaper ones instead of getting the SLPs again. This first set lasted about a week so I may have to go back to the SLPs. I am still using the bolts that came with the kit.

 

I just had my cars exhaust leaks fixed (had a broken header bolt in each side , im not a mechanical genius so I didnt touch it) . I ordered the slp kit to replace the ones that were on there and they are still on there nice and tight. Car runs better now altho I still have bank 2 leaning out the mix while bank 1 is running perfect. I still wish I could figure that one out. I get codes for bank 2 cat inefficiency. I dont think a bad cat would make that side think its runnin rich do ya ??? I sent a autotap log to Injuneer and he said my o2 readings on both sides look fine