I installed the test pipe and fujitsubo exhaust, the car seems to be stalling around 3-4k rpm all the time, even on the freeway. Also did the O2 simulator (electrical) and got the cel light. Anyone has any idea on the stalling? The car feels that it will die on 3-4k rpm if I don't press the gas and go over 4k. Is that normal? Seems like a lot of back pressure coming from this setup.
Any input will help...

 

No,It's not normal,and the TP and catback,alone,cannot do that.
Are you sure,the wiring for your electrical O2 sim.is OK??

 

I'll re-check that.

Is there any other possible explanation?

 

Can't see any.

 

yeah, the exhaust/tp would cause LESS backpressure. not more. start with that electrical O2 sensor. particularly because it's causing a CEL, it can be causing your problem.

 

what sucks is that was not me that installed the simulator and i can't get ahold of the guy but I need to locate the ECU so i can undo his job and just put back to stock and go for the mechanical simulator type. I'm new with the S2000, where's the ECU located on these cars. If anyone can post a pic or directions on where to find the ECU....

 

whats an electrical O2 sensor anyways?

 

There is an O2 sensor attached to the cat. When you put a test pipe on you need to simulate the effect of the cat or you will throw a CEL. There are electronic simulators that you can wire in to prevent the CEL. You can also mechanically prevent the CEL by using spark plug antifoulers as a spacer for the O2 sensor when attached to the test pipe. You can read how that works here:
https://www.s2ki.com/forums/index.php?showtopic=229959

 

do you know where's the ecu located?

 

Are you sure that he did not do the wiring under the car where the plug for the O2 sensor is? Every electrical simulator I have ever seen was placed down under the car as a "go between" for the plugs to trick them. I have never really like electrical simulators, my buddy went through them like water on his cobra..it was strange how they would just give up.

Good luck to ya man, hope things work out!