I have a 91 accord 4dr 5spd and the engine ran nice and strong when I got. The gas pedal was soft and acceleration respond quick. The accelleration acutually got better after I had my aftermarket header and down pipe installed and my muffler. Now that I just replaced my muffler with this muffler from ebay, I my acceleration became stiff. Click on link to see http://cgi.ebay.com/ebaymotors/FIT-C...QQcmdZViewItem

The exhuast tone got wrost and a day after it was installed, my check engine light came on. I did a diagnostic test and found code 43 which has something to do with the fuel system, fuel pressure or the O2 sensor. Now what I did was I reset my engine light and then I started the engine and reved to 3,000 rpm for pass three minutes and the engine light didn't come on at all. I thought that it might of just been a lazy O2 sensor. Now when I drive it doesn't come on all the time, but it comes on every now and then. My guess is that it could just be my muffler or maybe some related to the fuel system.