MOT Emissions advice please.

[Grey Area]

Afternoon all.

Recently had the exhaust replaced on the 230k with a straight through stainless job, including (stupidly?) a cat delete.

Just got the car back from the garage and somewhat unsurprisingly the car failed on emissions. However, it didn't fail by much at all.

Predictably it was the CO level that was a touch to high:
Fast Idle test 1: CO limit=0.3% actual value=0.39%
Fast Idle test 2: CO limit=0.3% actual value=0.41%

Oil temp was 92 degrees C and rpm speed measurements weren't recorded but must be between 2150 and 2850 for the test. Natural idle test levels were a pass as were all other emission tests.

So, the million dollar question, how to shave off 0.11% of my CO emissions?
Any help to destroy the environment gratefully appreciated

 

[AMGeed]

Time for the Italian tune up.
Take it for a legally, quick as you can, blast for a few miles just before having it retested.

You are fortunate your MOT tester didn't fail the car because of missing the cat. It's what they are supposed to do, but in reality hardly ever do.

BTW, my secondary cars are removed and the emission test was passed. No mention of missing cats.

 

[BTB 500]

BTW, my secondary cars are removed and the emission test was passed. No mention of missing cats.

I think so long as the car still has *some* cats you are OK. My SL only has 200 cell sports cats mounted at the back of the system and that's never been queried when MOT'd at a main dealer.

But no cats at all on a car that had them as standard should be an automatic fail, regardless of the emissions levels.

 

[clk55M]

I'd service the car and then as AMGeed pointed out, go for a blast. If this still doesn't do the trick, might need a custom race CAT. Maybe 500 cell

 

[Grey Area]

Thanks guys for the advice, I've got a free re-test tomorrow (today technically) so I'll try giving it a blast and then straight into the test, hopefully that'll do the trick.
Still clinging to the hope that I can get away without getting a sport cat, but I'll suck it up and buy one if necessary.

I read somewhere on here that the O2 sensors can make a difference, can anyone expand on that?

Anyone know a way to relatively easily change the fuel/air mix to lean the car out a bit for the test? Could make the crucial difference, although I seriously doubt this is possible.

And finally, indeed it should be an automatic fail, since I don't think the C230k has secondary cats, so it is cat free so to speak. Fortunately my mot tester is either exceptionally unobservant or feeling kind, I'm not going to ask him which it is!

Thanks again for the help so far chaps

 

[def90cars]

And finally, indeed it should be an automatic fail, since I don't think the C230k has secondary cats, so it is cat free so to speak. Fortunately my mot tester is either exceptionally unobservant or feeling kind, I'm not going to ask him which it is!

Thanks again for the help so far chaps

I would argue he can only retest on what it failed on - so if he didn't fail it on no cat, he can't retest now....???

Also no law about having a special "MOT" exhaust for 1 day per year. Maybe not strictly moral or legal from some regs, but certainly not breaking any MOT rules.... bikers with two number plates and off-roaders with two sets of tyres know about this.

 

[Grey Area]

I would argue he can only retest on what it failed on - so if he didn't fail it on no cat, he can't retest now....

Ha, hadn't thought of that! If he notices today I'll be sure to make that argument

 

[markmifsud]

Anyone know a way to relatively easily change the fuel/air mix to lean the car out a bit for the test? Could make the crucial difference, although I seriously doubt this is possible.

You could try a VW remap

 

[edtzxr]

One tip I have and had to use every time for mot on my old MGF was to get a redex or similar mot prep treatment from Halfords.
two bottles one injector cleaner and one petrol treatment how ever you need to get through two tanks of fuel for full effect. Use premium fuel and Also changed the air filter and the plugs and did the "Italian tune up" used to scrape through every year by the skin of its teeth. (car did have a cat but there was nothing left inside it!)

 

[Grey Area]

I did think about sticking a bottle of redex in it, however, I heard it can make emissions worse in the short term as it actually cleans the injectors and the sh*t is thrown out down the pipe. Could be nonsense of course.

Re-test in a little while so it's going out for run shortly, if it fails again then it will have to be new plugs and K&N filter and maybe a new O2 sensor.

Thanks to you all for your help.

 

[edtzxr]

http://www.amazon.co.uk/dp/B00BOP0YUQ/?tag=amazon0e9db-21

This is the stuff I used to use

 

[edtzxr]

http://www.amazon.co.uk/dp/B00CV60NDU/?tag=amazon0e9db-21

Sorry no it wasn't it was this one

 

[markmifsud]

So the question is, did the Italian tune up get a pass? or did you walk home.

 

[Grey Area]

It failed. Worse values than yesterday. I've come to the conclusion that the garage is blissfully unaware that there is no cat. Or there's a tiny chance that there's a second stage one in the back box, which is poached from a c36. Can anyone confirm or deny?

The garage is essentially next door however, so it's a short walk thankfully.

I've decided that I'm going to my indie tomorrow to get some live fuel trim data because I've become convinced the car is running rich anyway, so also considering a new O2 sensor for two reasons.

Here's a question for you all, if I unplugged the supercharger, would the ECU respond by trimming the fuel right down, to compensate for the lack of forced induction? This might help the CO levels. Or I could be talking rubbish.
The garage wouldn't let me test the theory with their mot exhaust gas doodah.

 

[markmifsud]

wouldnt that illuminate the MIL which is also a MOT failure?

 

[CHRISCHANCE]

I remove the air filter and give a blast down the motorway on the way to the garage for mot tests. Never had a fail on emissions yet. And that goes for diesels too.

 

[John Jones Jr]

It failed. Worse values than yesterday. I've come to the conclusion that the garage is blissfully unaware that there is no cat. Or there's a tiny chance that there's a second stage one in the back box, which is poached from a c36. Can anyone confirm or deny?

The garage is essentially next door however, so it's a short walk thankfully.

I've decided that I'm going to my indie tomorrow to get some live fuel trim data because I've become convinced the car is running rich anyway, so also considering a new O2 sensor for two reasons.

Here's a question for you all, if I unplugged the supercharger, would the ECU respond by trimming the fuel right down, to compensate for the lack of forced induction? This might help the CO levels. Or I could be talking rubbish.
The garage wouldn't let me test the theory with their mot exhaust gas doodah.

Howdo GA?

As per the guys stated. Loads of fuel system cleaner and an Italian tune up. I'd first disconnect the battery and let the ECU readapt, 200 miles on my 230K. Also consider removing and cleaning the o2 sensor, place the the tip in vinegar for a good few hours then rinse and dry. Or fit a new sensor if it's original. All of the above may or may not help but should be beneficial to the general engine performance.

As for disconnecting the S/C, I can't advise as I'd never consider doing that . I think it may run richer? And there's no Cat in a C36 backbox. I think you are going to struggle getting it to pass without the Cat. If the worst comes to the worst have the new pipe fitted with a two flanges along with a decat pipe matched to the cat, then you can fit and remove the Cat a will.

 

[Grey Area]

Morning all,

So my indie checked the car over this morning and mixed emotions were felt when he said all was well, on the one hand having something to fix and therefore maybe help pass the mot would have been nice, but it's also good to hear there's nothing apparently wrong with the car.
A couple of points he mentioned were; that the car is designed to run with some back pressure and by eliminating that, the car is trying to compensate and probably is running a bit rich but couldn't confirm with diagnostics apparently, incidentally this is also causing a slight 'blip' or 'stumble' every now and again in the engine when you hold it at a fast idle.
Furthermore, that yes JJJ, disconnecting the S/C would indeed have the exact opposite effect to what I said and in fact make the car run richer and dirtier.
Finally, while fitting new O2 sensor and spark plugs etc could potentially help it would be difficult to get the car running at that magic 0.3% CO and I should probably suck it up and buy a cat.
So, in conclusion, I think I'll try redex and fuel additives, cleaning the O2 sensor and then stick it in for one more MOT with a garage I suspect is even more dubious than the last one then it'll be off to the catalytic converter shop if it's still no good.

@jjj, 30 mins with the battery of should reset the ecu? It's tricky to get 200 miles on the clock with no MOT, but just about doable in darker parts of east anglia. Any thing to watch out for when removing the sensor?

Thanks to all for the sage advice.

 

[John Jones Jr]

I don't think it's anything to do with less exhaust back pressure, well that's my unqualified view.

The 'stumble' you report might be solved by having the throttle body adaptations recalibrated, I think this can only be done via STAR?

20-30 mins should do the job.

Ideally, you need an o2 socket. These have a split on the side wall to allow the cable to be moved to one side.

Let us know how you get on.

 

[Mercedes man]

Hi pop down to eurocarparts and get some stuff called cataclean tip in tank should be job done