SigSauer40

Well as the title states.
I have a 1994 z28 lt1 that I just got as a project car the first thing I have done is remove the stock exhaust system and catalytic converter and installed a 40 series flowmaster right after the turn under the passenger seat were the stock catalytic converter was....now I have read many other posts about back pressure and what not but anyways after have done this I now have a misfire and also a loud pop after a Rev to about 2500 3000 rpms. but the guy I got the car from used a piece of flex exhaust in the bend and making the turn before the exhaust so I'm about 98% sure that the loud pop is coming from that being open or having a gap on each hand and when I let off of the throttle it's sucking air into there and making it pop but I am more worried and trying to fix the misfire issue any suggestion would be helpful thanks

Injuneer

Description of the exhaust system is unclear. Do you still have the stock manifolds and y-pipe? Where is the flex pipe located? Y-pipe was welded to the stock cat. Appears that was cut off, and a flex pipe added between the Y-pipe and the muffler???

If the O2 sensors are exposed to a backwash of air, it's going to run rich, which can cause a misfire and a pop. Backpressure has nothing to do with it.

SigSauer40

Yes car has factory manifolds. An they drop down into a single pipe (Y) pipe n then immediately after that the curve in front of the oil pan toeards the passenger door os wjere the flex pipe is. Hopefully today I can get by my shop and put new fresh pipe in n lengthening system will help. Hopefully..