MOT emissions

Well my 2002 135 TF just scraped through on emissions, which surprised the hell out of me, why?. Well last couple of years it has sailed through, but I had been patching the back box, so a few weeks ago I went to replace the back box, but the joint with the cat was one complete lump of rust, so I had to cut it off and replace the Cat as well, and the sensor to be on the safe side. Now, less than 100 miles later, it only just passed the emissions test. What that all about?

Was the cat a genuine one or a pattern part?

Are the sensors ok and plugged in firmly?

Did it get an Italian tune up prior to the test?

Type Approved Cat, sensor tight and plugged in properly, Engine,Cat warm from medium Italian tune-up up

The wifes F just about scraped through emissions on the last mot and was advised on a slight blow on the flexi.

I fitted one before the last months mot and I flew through the emissions.

Maybe have a look there.

Other than that maybe a set of plugs in it may sort it.

Good thing though is you've got 12 months to sort it out!!

Ah now, you may have hit upon something.To get the Cat and the old back box off took quite a lot of pushing, pulling, etc, and the Flexi is almost certainly the original, I wonder if it might have a blow in it now.

Start it up and see if it is.

Although hers was blowing you couldn't really hear it but there was a soot mark where it was split.

Sounded really quite when done.

Would it be worth disconnecting the battery for an hour or so to reset the ECU? Although compensating for the old cat would probably have the opposite effect with the new one fitted, and 100 miles should be sufficient to relearn.

Don't suppose you have the values of the emissions? Or know what parts were high?

"Type Approve CAT" can still mean a cheap one with nowhere near as much honeycomb catalyst as a genuine one. I don't know what it cost, but that old saying of "buy cheap, buy twice" is certainly true with CAT's. Some of the "approved" ones have half as much catalyst as genuine ones.

My mgtf sailed through mot's. ..until one year I was shocked has they said emissions were high...they did say I needed a new flexi has it was leaking...thinking that was the cause of the high emission reading I stripped off the full exhaust system and replaced the flexi pipe and renewed all gaskets on the system...cleaning up the flanges and replacing the studs...tidy job and saved me pounds from the original garage quote...has they want to give you a full system......on the retest I was shocked has they said the emissions were still high and it would not pass the mot....after a few discussions the sensors were the first port of call...but I was amazed at the next call which said the garage had put the car on diognostic and cleared a fault....the car was now well in the limit and had passed the mot....well that was my mot emission story....🤗

It wasn't a really cheap cat, mid range I would say.

CO2 failed 1st Fast idle test at 0.35% vol, pass is 0.30
lambda 1.021 pass is 1.09
HC 71 ppm vol pass is 200

passed 2nd Fast idle test just on CO2
similar HC and lambda.

So CO2 was main issue, never was close with old cat/backbox/sensor.

as I said Cat not cheapie, back box was quite cheap, proper sensor.

But will definitely check Flexi as per Andy, when I can feel my fingers, cos I am pretty sure it was the original and it could easily have been damaged by the pulling and pushing to get the old cat and back box off.

Will also check for fault codes as suggested.
cheers gents

Haven't had a chance to do much checking, but did start her up and feel around underneath. No sign of blowing from flexible, but did find a small leak from top of joint between cat and back box. Didn't use sealant just the metal gasket. Do you experts think that a leak in this joint, past the Cat could cause the higher CO2 readings?

My last MOT, the tester was scratching that the emissions were too high, then he suddenly smiled and said, put this rubber pad over the left hand exhaust tailpipe and block it off.
The emissions dropped to well below the level required.
My TT Mk.7 draws in air from the passenger tailpipe when idling and recirculates it in the back boxes and throws it out of the right hand tailpipe along with the engine exhaust gasses.
It sends the O2 reading through the roof.
If you have an aftermarket exhaust, make sure that both tailpipes are venting, or block off the one that is lazy and send the probe up the other.

Sundance