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I had purchased and recieved a y-pipe finally and a staight pipe wich is resonated from custom maxima. My muffler guy told me since the o2 sensor is behind my cat, that I need a simulator. He said that it will make my car run like crap with out it. If the o2 was in front of it, acording to him, I would not need a simulator. So I am asking you guys if this is true? Anyone running one of these? Thanks for the help! I dont want to get beat buy the sheep because of a mod I thought would make my car faster.

 

the o2 sensor behind the cat only monitors the cat. it does not control a/f ratios like the 2 primary o2 sensors that help control it at all times but WOT. most likely, replacing the main cat with the straight pipe will set off the ses light. you can pick up a simulator for around 30 buck shipped.
go to o2simulator.com and check it out. if i were you, i would get the install out of the way and see what happens. no need to spend it ahead of time if it does not come on. the simulator is very easy to setup.

 

When I put in my straight pipe I got a code after about 300 miles of driving. I reset it and never got it again.

 

No, your car will not run like crap but you may get a CEL. This is also not the forum for a question like this.