So I purchased my 93 FD here in Japan, and they previous owner attempted a few common mods. Such as a crappy battery relocation, but more annoyingly a CAT delete job that was.... Half assed. So the O2 sensor is neatly tucked away and the piping is in good shape, but the hardline running from the air pump to the CAT was just left wide open. So it makes a loud annoying noise at certain RPM and the car runs rich as hell unless I unplug the air pump; backfiring endlessly. Am I best off leaving this thing unplugged? I have ZERO experience in emissions delete jobs but this definitely seems like an incomplete job here, Any recommendations on how to finish this dudes work?

 

It's refreshing to know that people are still doing half as work out there for the sake of doing it. You need to find a stock cat and put it back in and undo those mods. If you're on a stock ecu then it's only a matter of time before you cause some serious damage. If you're on a power fc then it's only a matter of time until you cause some serious damage. Find a stock cat and put everything back to normal. Also fix that crappy battery relocation. Putting little effort into wiring jobs can lead to shorts and fires. Neither of which are usually easy to come back from.

 

A little late to this but I'm confused. The O2 sensor is/was in the down pipe/pre-cat of our USDM cars...not in the inlet of the converter. Otherwise I agree with cr-rex, it sounds like the easiest thing to do is add a cat back in. And you eliminate any risk of boost creep in the process and the car won't stink. Performance won't noticeably change.

 

I think he's referring to the exhaust temp sensor.

 

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On the stock ECU the car may even idle and run better off of initial throttle with the cat returned. A good hi-flow cat like Bonez would also work.