test pipe - cat replacement

[Otismo]

I just put a 3" Cat-back ( well, O2 Sensor back ) Magnaflow exhaust on my 99 taco. It's not quite loud enough for my tastes, so I'm putting a 2.5" test pipe in place of the catalytic convertor hoping for better results. I would imagine this will screw up my rear O2 sensor and throw off the check engine light. I was wondering if there's any way to re-adjust the O2 sensor somehow so it will read correctly. Would I be able to somehow splice the back sensor into the front sensor and it would read correctly? Or is it looking for 2 specific different readings from the entrance to exit of the cat? I don't want to screw up my fuel mixture or anything of the sort.

[Brian R.]

The front sensor is for regulating fuel/air ratio. The rear sensor provides the computer with a warning about the effectiveness and function of the catalytic converter. The two sensors do not have the same function so they must remain independent.

If you want to eliminate the catalytic converter, you would have to measure the signal or determine the expected signal from the rear sensor and duplicate it with a battery or transformer. Otherwise the CEL will come on.

I don't think that the cat. converter is adding much back pressure to your system. The muffler and the exhaust manifolds are the main contributors to back pressure. There is where you need to concentrate your efforts. Headers will do alot more for your engine than mucking with the cat. converter.

[Otismo]

Thanks for the info, I'm glad to know that it won't mess with my ratios. I can deal with the check-engine light, although I'll never know if there's something really wrong. The main reason for getting a test pipe wasn't to reduce back pressure though. Headers will come in time. I was just not satisfied by the volume of my new exhaust - I'm just looking to make it a bit louder. Come to think of it, is there some sort of tutorial on faking out the O2 sensor...I'd rather not have the check engine light on steady just in case it actually needs to come on for a legit reason.