I had a new muffler installed a couple of weeks ago. I believe 2.5" pipe straight through to 4.5" outlet (Naxos). Anyway, right after that I started to notice that on the shifts from second to third or even on some others at times, the transmission hesitates for about a second, and then shifts... I was just wondering if this may have been because the computer is not used to the different amount of backpressure. btw, the muffler sounds great! Thanks for the help, and let me know if that sounds like the ECU just needs to be reset.

Amit

98 SE auto

 

There is no sensor which measures backpressure so the Engine Control Module (the computer) isn't aware of the change. You may reset the ECM if you like, it won't hurt anything, but don't expect it to affect the shifting behavior.