Catalyctic converter and NCT?

ardle1

Hi! thought I'd give this Thread a new lease off life.
So what's the latest, will my car fail NCT Emissions with just straight pipe(decat)catalytic converter removed, assuming she always passed emissions with cat. And what difference as in noise, power, speed if any will it make!
:2001 VW Passat 1.9Tdi AVB Engine.

biko

Moved out from old thread

Short answer is: it will fail nct. Emissions will be off.

challengemaster

Diesels don't have an emissions test

biko

Well spotted, there is a smoke test but I don't know if it would fail that.
This is the nct manual
http://www.ncts.ie/NCT%20Manual%20Revise%20May%202012.pdf

Sir Arthur Daley

I cannot see why not.

challengemaster

biko wrote: »

Well spotted, there is a smoke test but I don't know if it would fail that.
This is the nct manual
http://www.ncts.ie/NCT%20Manual%20Revise%20May%202012.pdf

Cat has no effect on smoke tbh. Excess smoke is either due to excess fuel being dumped out the exhaust, or oil being burned.

It'll pass, if the engine is in good condition.

dougie-lampkin

challengemaster wrote: »

Cat has no effect on smoke tbh. Excess smoke is either due to excess fuel being dumped out the exhaust, or oil being burned.

It'll pass, if the engine is in good condition.

The smoke test is no problem, as you say the cat itself has no effect on smoke. But it's a failure to remove any emissions equipment. If the cat is usually visible from underneath, you'd be failed on it. Ideally you should gut the cat and weld it onto the pipe, so that from the outside it looks like it's intact. The NCT man won't be looking inside

Also worth noting a decat will have zero effect on power, but could actually help reduce smoke. With the cat in place, the turbo is trying to push exhaust through the cat rather than compress the charge. Remove that restriction, and it will spin up faster and lower down. More boost = less smoke.

Chimaera

Not having a catalytic converter will have little to no effect on the smoke test. But they do a visual check too on the system.

From page 11 of the NCT manual:

1.
Check visually that the emission control system is complete and properly connected and that there are no leaks in the
exhaust system.

This doesn't explicitly refer to the catalytic converter, but if they inspect the system and find it missing, I'd think this rule gives them the leeway to fail you.

challengemaster

I've yet to hear of a diesel failing for having no cat

Chimaera

From what I've seen and heard, they're going after the smaller things in the manual now. All the low hanging fruit is picked clean so the opportunity is there now to tighten up on the small stuff that was simply too onerous to chase in the early days.

dougie-lampkin

challengemaster wrote: »

I've yet to hear of a diesel failing for having no cat

I've had no trouble with mine, but I always leave the shell welded on. It is pretty clear it's a failure though, whether or not the tester picks up on it.