De-catting and new MOT rules

[Mr Whippy]

I'm pretty sure this website reflects the new rules
http://www.motuk.co.uk/manual_710.htm


There are three columns. The first is just general info.

The 2nd column is populated with test criteria from 1 to 5.

The 3rd column contains the rejection reasons from 1 to 5.



It does appear that the test criteria line up with the rejection reasons.

Hopefully this means that if a rejection reason shows up on your MOT, it shows up in correspondence to the test criteria that would cause that rejection to be used.
In this case the test criteria to offer a rejection on a missing catalytic converter where one was originally fitted, is that the car cannot undertake it's full catalytic converter emissions test, thus the car has to be rejected.


However, it doesn't appear that any current UK DERV undertakes a full catalytic converter emissions test anyway, still only a smoke density test is undertaken.

Thus it seems that running a de-cat on a DERV is totally fine under the new MOT rules. The test that allows the 'missing cat' rejection to be used, shouldn't be used on our exhaust system check list anyway.


I can only see an issue where MOT testers just apply column 3 rejection reasons irrespective of the reason why they are applied... in this case they would have to apply a rejection that technically can only be applied to a car that has a full cat test.


I think these new rules are MORE clear than the old ones which are vague in this area. However, the fact the test criteria and rejections are split might mean some testers decide to start interpreting the rules and failing cars for missing cats when they don't need full cat tests (all DERV are smoke density only)





I'm assuming other people agree with my interpretation of this? Or do people think column three rejections should be applied irrespective of what appears to be a correlating test criteria in column two?


It's obviously really important for us to be clued up in this area as we go forward due to the prevalence of us de-catting our HDi's!

Cheers

Dave

[declantg]

Is it the same on the XUD engines?

[Mr Whippy]

Technically it's identical yeah.

DERV = no full cat test.

No full cat test = no ability to fail under no cat fitted rule.

[declantg]

Thank f*ck for that!

[darrenjlobb]

Hm im not sure, I don't think there meant to line up....

Pretty sure its meant to have one fitted if it had one from factory, which for XUD owners is no issue as you can say it didnt have one...

Recently did a 2.2 hdi for someone, particle filter system was fooked, so smashed it out / mapped it out, and after speaking the the guy, he said it NEEDED a cat to pass, obviously I kept quiet as I knew fuill well inside it didn't have one, but as the outer bit was still there, he thought it did, so would seem he would have failed it if it wasn't present, but obviously that's a new one thats probs eligible for full emissions or shit like that...

[Mr Whippy]

Well this is the thing.

There is some vagueness in the correlation of test criteria and rejection reasons.

I believe they are intended to line up if you read them. However, I can easily see how someone could 'say' they were not meant to and apply them willy nilly.


I had a quick look for a contradictory example, but stopped to get on with other stuff. I'm pretty sure if you use the logic of using any rejection reason irrespective of the test criteria you could fail a car for almost anything.


So the question really is, do the test criteria/rejection reasons correlate. They would appear to in ALL sections. However, if your tester follows that logic or not is another matter.

I'm sure there is a page on how to use those guidelines, I'll look later.


But for now it is as it was before with the old rules. Technically it was ok, but if you had a pain in the arse MOT tester they could twist the rules to fit their desire to fail the car on a missing cat (missing part of exhaust criteria, despite it meaning literal part missing and an incomplete system, not a part missing but otherwise replaced to form a complete system)


New rules, new interpretations

Dave

[Toms306]

Yeah they should line up....look at number 5 on there, the regection ONLY applies to number 5 on coloumn 2.

The way i interpretted it only emmisions tested vehicles need a cat....no emmisions test for deisels (yet!) so should be fine with a decat imo.

[Midnightclub]

Or just do what i did.. cut open the cat, remove all the internals and clean it out then weld it back up again.. still has a visible cat and can't fail the smoke density test

[Poodle]

Completely agree with your interpretation Dave, as do both my local MOT testers and a couple of mates in the business. It says "On vehicles that qualify for a full cat emissions test, check the presence of the catalytic converter", which in our minds clearly implies that if the vehicle in question does not qualify for a cat emissions check, then it cannot be failed for not having one.

Quite reassuring since neither of my testers are particularly sympathetic towards modified cars, and one of my mates in the business is actually anti-modding - thinks "life would be easier if the govt grew a pair and banned it already".

[darrenjlobb]

If thats the case, then its pretty good news, as that would totally rule out cats being needed on these, which would clear up alot of grey area issues...

[Ruan]

You can't check the Cat on a diesel for how well it's working unless you were to put it on a dyno and get the engine up to proper operating temperature and then cruise for a while and measure the NOx and HC output - which they can't do.... Any other time it's not operating properly as it's not under enough load, you might get a bit of NOx on idle, but generally the combustion temperature is nowhere near high enough to cause NOx to be produced...

And as of yet, there's pretty much NO reliable way of measuring NOx content in exhaust gasses...

[Toms306]

And as of yet, there's pretty much NO reliable way of measuring NOx content in exhaust gasses...

Thats good then....I expect EGR deletes would be a fail otherwise!

[Ruan]

But NOx is almost impossible to measure reliably...

NOx is a sign of a HEALTHY engine, if you catch my point, the fact it produces NOx is a GOOD thing as far as the engine is concerned, it means the combustion temperatures are good and you won't get much unburnt/part burnt HC, it's just that the earth doesn't like it so much!

I can't see a way they're going to measure if the NOx output is too high on an engine any time soon... Thing is, if you delete the Cat without removing the EGR system, you're likely to produce loads of CO - as the engine is burning very close to stoichiometric, any slight deviation will cause HC and CO with no Cat to rectify that...

[Toms306]

But NOx is almost impossible to measure reliably...

NOx is a sign of a HEALTHY engine, if you catch my point, the fact it produces NOx is a GOOD thing as far as the engine is concerned, it means the combustion temperatures are good and you won't get much unburnt/part burnt HC, it's just that the earth doesn't like it so much!

I can't see a way they're going to measure if the NOx output is too high on an engine any time soon...

Yeah I see what you mean, and the earths f*cked anyway...our parents generation ruined it so not much point worrying about it now!