MOT emissions fail after secondary cat delete

[flango]

I also wonder about the longevity of some aftermarket sports cat - even if it gets through the first MOT, how many subsequent years will it pass for.

I would be erring on the side of welding the original cats back in myself as long as they do a reasonable job of it. It should be pretty easy as the could just sleeve it either end.

There were cars we did mostly Subaru and EVO I admit, but the sports cats on those things would be only good for 18 months - 2 years max. This is in line with my own experience on SWMBO A8 fitted 2 x sports cats and new O2 sensors, flew through MOT Immediately, 12 months later still passed but had dedteriorated with higher emissions readings, 20 months later both cats had failed miserably and these were high end cats not the cheap ones you can pick up for a couple of hundred quid

 

[BTB 500]

Hmm ... thanks guys. Food for thought.

Will have a look at the current emission figures (no cats) to see how big the difference is compared to last year's MOT.

Incidentally, far from trying to sell me a replacment OEM system the guy at the dealership (service team leader) suggested getting a bolt-in set of cats that could just be put in at MOT time!

 

[IanA2]

In view of the other Ian's observations, I'd be inclined to get the originals put back on.

 

[Sp!ke]

In view of the other Ian's observations, I'd be inclined to get the originals put back on.

Problem is though BTB is now addicted to the noise his car makes.

 

[IanA2]

Problem is though BTB is now addicted to the noise his car makes.

Addictions can be expensive.....

 

[DSB SL AMG]

Easy then, you now have a solution

Hmm ... thanks guys. Food for thought.

Will have a look at the current emission figures (no cats) to see how big the difference is compared to last year's MOT.

Incidentally, far from trying to sell me a replacment OEM system the guy at the dealership (service team leader) suggested getting a bolt-in set of cats that could just be put in at MOT time!

 

[BTB 500]

Unfortunately I can't be bothered with swapping bits of exhaust over!

I would be reluctant to go back to a standard setup ... the whole point of the changes was to get a bit more noise. But obviously I want to be able to get through the MOT!

The failed emissions test ticket from Tuesday doesn't give any of the actual readings, which is weird?!

With the M-B cats it was well under the limits last year:

Fast idle CO 0.06 (limit 0.2)
Fast idle HC 36 (limit 200)
Fast idle Lambda 1.011 (allowed range 0.97-1.03)
Natural idle CO 0.00 (limit 0.3)

So I'm hoping that sports cats will be OK, but I will discuss with the exhaust place first and keep the original cats just in case.

 

[IanA2]

Unfortunately I can't be bothered with swapping bits of exhaust over!

I would be reluctant to go back to a standard setup ... the whole point of the changes was to get a bit more noise. But obviously I want to be able to get through the MOT!

The failed emissions test ticket from Tuesday doesn't give any of the actual readings, which is weird?!

With the M-B cats it was well under the limits last year:

Fast idle CO 0.06 (limit 0.2)
Fast idle HC 36 (limit 200)
Fast idle Lambda 1.011 (allowed range 0.97-1.03)
Natural idle CO 0.00 (limit 0.3)

So I'm hoping that sports cats will be OK, but I will discuss with the exhaust place first and keep the original cats just in case.

Good thinking..

 

[flango]

Remember fitting sports cats will also change the noise from what it is now, it will quieten it down but not to the levels as the original set up.

 

[BTB 500]

Yup I'm assuming sports cats will be a little louder than the M-B ones were.

It's a shame in a way as the current setup (no cats) isn't excessive by any means - I guess the back box is reasonably efficient. I'd be reluctant to open that up and start attacking the baffles as it's a genuine AMG one (£££) - if necessary I could follow Sp!ke's route and look out for a cheap standard rear box and experiment with that.

 

[BTB 500]

So just to close this off.

Car went back on Tuesday to have 200 cell sports cats fitted. I was assured they would be OK for the MOT, and in fact they provided an emissions test readout (they are also an MOT station) as part of the process. Back to M-B Guildford for a (free) re-test today and no problems

As expected the sound is somewhere between the original setup with M-B cats, and how it was with no cats at all! Sounds nice when driving ... some noticeable rumble at low speed which was absent with the M-B cats. It's also lost the slightly annoying metallic rasp that the non-cat system had at about 1500 rpm.

One slightly odd thing I noticed is that the new cats are towards the rear of the system rather than straight after the downpipes. Not sure of the reason for that but doesn't seem to cause a problem.

Just after giving the car a wash today:

[YOUTUBE HD]5FLwN7hma4c[/YOUTUBE HD]

 

[IanA2]

Was the wallet damage excessive?

 

[BTB 500]

£475 in total.

 

[IanA2]

Gosh....that seems very reasonable indeed

 

[C43AMG]

Sounds okay Bill.