I have a 98 fd and one the previous owners have removed the airpump, acv, etc as well as the cat, seen a few posts online here about this subject but no clear answers

I want to pass uk mot test however buying the entire airpump, acv and all that seems near impossible and very expensive so I guessed I only have a few options

1 - run a cat without an airpump at all
2 - run a cat with the airpump just pushing air into it at all times as its belt driven

which is best and will #2 burn up the cat if the pump is always pushing in air

The acv also pumped air into the exhaust ports but not sure what benefit that serves versus jump pumping into cat

 

explanation of the air pump and ACV here: "Why is this engine so damn complicated??" Part 2: Emissions controls - RX7Club.com - Mazda RX7 Forum

it's probably going to be hard to source an ACV for anything past series 6 cars (96+). I don't have experience with the 96+ ones (were never sold in USA), but if you can put it directly into the exhaust ports I would try that first. The stock ECU is designed to work with it that way under most situations.

 

there have been some people who ran the air pump right to the converter, which would do something, although not as good as using the ACV