MOT Failure.

[DaveEssex]

Let me be honest and simply say that a year ago I bought a clean 2006 Hawkeye with a new MOT, and no plan in the first year to do much with it, hence only a couple of low key events and little mileage on the clock.
The MOT is now due, and I needed to check for myself what would be the outcome of leaving it as purchased with a non-cat exhaust. I expected it to fail, and it did (only on excessive CO).
I would appreciate simply to learn what are my best options before I go all out and purchase a catalyst and, if needed, a full system just to pass on am MOT retest, and then remove.
The car is a WRX STi SPEC "D" in almost perfect condition with no cat, (and no secondary cat/expansion box) a 3 inch straight through system into a single simple back box with a loud 3 1/2inch back pipe.
Forgive me for being a life long mostly BMW, Classic and modern Jaguar and Porsche Carrera driver, ready to learn how to enjoy my Scooby over the coming years.

[davidexige]

Has it had both cats removed? There's one in the downpipe as well as the secondary cat. I think what you call the secondary cat/expansion box is a de-resonator. I removed the secondary cat from mine and never had a problem with emissions apart from last year where it failed on slightly high CO, in my case it was a defect MAF

Edited by davidexige on Friday 20th October 13:41

[MDMA .]

Just need to fit the primary cat -

https://www.haywardandscott.com/subaru/impreza-new...

Or if you can, a sh Prodrive sports cat ( have one fitted to mine ). Passes MOT no problem. Try Matty at MBDevelopments. He is always breaking STI's.

[vxr2010]

The permanent option is fit a sports cat and then get it mapped , the non permanent is get a bolt in section one with a cat for mots and one with out .. sounds like hard work changing it for an mot each time , easier going the sports cat route , the only cat you need is the down pipe

[Konan]

vxr2010 said:

The permanent option is fit a sports cat and then get it mapped , the non permanent is get a bolt in section one with a cat for mots and one with out .. sounds like hard work changing it for an mot each time , easier going the sports cat route , the only cat you need is the down pipe

Yeah, the mid section one would be reasonably easy to swap for MOT time compared to the primary, so long as you keep some spare bolts for the donute gasket joint. Primary is more of a pain as you have to fight turbo studs and replace the gasket each time etc.

May not need mapping putting a cat back in - would have to log and see. A lot of the 'thou shalt map' when you improve flow on the exhaust is down to the STi turbohaving a real habbit of boost creeping, so you need to set WGDC max down.