Failed MOT - Emissions

[BackUpTerry]

Hi all,

I'm hoping someone could impart some words of wisdom please.

My newly acquired MK3 failed today on emissions and handbrake travel. Handbrake I can sort but scratching my head at the emissions so hoping someone could maybe give me a shove in the right direction.

CO 3.3/3.9
HC 120/145
Lambda .927/.910

The previous owner/s have fitted a stainless manifold, aftermarket backbox and a new cat in Jan last year. Looking at receipts it also had spark plugs last year.

Looking at graphs for the MAF/02 sensors on my torque OBD2 app they seem to be reporting ok when accelerating, raising and dropping as expected (between ~.2 and .9), though not sure how much I should rely on this?

One thing I realise I did wrong was not running the car very much before the test - only drove around 10 minutes beforehand and I see online many recommending ragging it before the test, would that cause such high figures though? MOT bloke recommended a fuel treatment

I've tried to research and most threads seem to indicate MAF/02/CAT. No EML, no codes. No smoke out the back when warm either.

Thanks!

[nick]

Certainly give it good long run and then make sure it is warm for the test.

[Topdownman]

Yes, definitely a good, hard run beforehand and try to keep it running while you are waiting to get on the ramp. The figures dont mean anything to me but I would check the condition of at least one sparkplug to see if there is anything obviously wrong such as sooting up. I would run a bottle of redex through the car just once to help clean it up if the car was new to me. Also worth cleaning the MAF as very easy to do and can cause problems if dirty. Also wide mouthed exhausts can cause problems with readings but not much you can do about that. If its a sports cat that was fitted, even more important to get it up to temperature as there will be less leeway on iuts performance. Good luck.

[BackUpTerry]

Thanks for the responses. Some good suggestions top down.

Current plan is check plugs for soot, clean MAF, bottle of cataclean beforehand diluted with premium fuel and a good thrashing before the test. I'm not too fond of wasting the retest but would rather try this than go down a rabbit hole looking for problems that might not exist.

Looking at Tuesday for retest so I'll update with results.

[jimi]

If it's not been done recently, then it's worth doing an oil change as well.