Cats / Emissions 3.0si Coupe

coupedan · Post by **coupedan** » Mon Apr 24, 2017 11:36 am

Just had my MOT which passed with no advisories

However, the tester noticed that my emissions on the "Fast-Idle" check were struggling to get under the Max threshold of 1.030ppm mine was at 1.027ppm. He said he had to test it 3 times to get it under as the first 2 were over the max.

So my questions are.. Has anyone had any experience with the cats failing on a 3.0si?
Is it likely to be first or secondary cats?
Could it be the lambda sensors are failing?

If it is the cats.. are there any performance gains to be had by installing sport cats, if they are available?

Car info..
It gets run on Shell V-Power Nitro+ with a fresh tank at least once a week.
Gets driven daily fairly hard - After all it is a sports car.
Before my MOT - I gave it the good old fashioned "Italian tune-up" to heat up the cats.
Car is a 2006 Coupe with just under 115k miles on the clock.

Any advice will be welcome

Dan.

RyanB88 · Post by **RyanB88** » Mon Apr 24, 2017 11:52 am

I don't think it'd be to do with the secondary cats as our engine can pass it's MOT with them removed (as long as they look like they're there visually!)

coupedan · Post by **coupedan** » Mon Apr 24, 2017 12:30 pm

RyanB88 wrote: ↑Mon Apr 24, 2017 11:52 am I don't think it'd be to do with the secondary cats as our engine can pass it's MOT with them removed (as long as they look like they're there visually!)

Ahh.. this was my worry as I know the primary cats are in the manifold - could be potentially costly me thinks!

RyanB88 · Post by **RyanB88** » Mon Apr 24, 2017 12:32 pm

coupedan wrote: ↑Mon Apr 24, 2017 12:30 pm
RyanB88 wrote: ↑Mon Apr 24, 2017 11:52 am I don't think it'd be to do with the secondary cats as our engine can pass it's MOT with them removed (as long as they look like they're there visually!)
Ahh.. this was my worry as I know the primary cats are in the manifold - could be potentially costly me thinks!

I wouldn't worry about it yet, you should have at least 12 months ! You may find if you take it to another garage next year they might find their systems don't have the same troubles with getting the emissions right!

coupedan · Post by **coupedan** » Mon Apr 24, 2017 1:25 pm

This is true.. although I would much rather sort it ASAP rather than get round to MOT time next year and be hit with a £5k bill...

Mr Tidy · Post by **Mr Tidy** » Mon Apr 24, 2017 9:01 pm

I wonder if it says more about the tester's equipment than your car - which is a lovely choice of Z4 by the way!

Mine had an amber EML light come on last year which my BMW indy said was due to a cat fault. He cleared it and I made sure I only used it for spirited, longer distance drives and it's been OK since - thankfully!

It hadn't long passed an MOT so I asked why it would have passed that and he told me the threshold on the OBD set-up is set at a more stringent level than the MOT requires. He also said new cats would be in the £2K bracket, so I wouldn't rush to replace them as a preventative measure!

coupedan · Post by **coupedan** » Tue Apr 25, 2017 2:25 pm

Mr Tidy wrote: ↑Mon Apr 24, 2017 9:01 pm I wonder if it says more about the tester's equipment than your car - which is a lovely choice of Z4 by the way!

Mine had an amber EML light come on last year which my BMW indy said was due to a cat fault. He cleared it and I made sure I only used it for spirited, longer distance drives and it's been OK since - thankfully!

It hadn't long passed an MOT so I asked why it would have passed that and he told me the threshold on the OBD set-up is set at a more stringent level than the MOT requires. He also said new cats would be in the £2K bracket, so I wouldn't rush to replace them as a preventative measure!

Thanks

But could be the testers equipment to be fair.. it easily flew through last year but it has also been smelling ever so slightly "Catty" (not the egg smell but the metallic burning type smell) that you get once a cat is on its way out.. so does beg the question.. are the cats on their way out.?

It's good to know that the OBD values are more stringent than what an MOT would test, plus I have had no engine warning lights so it should be fine.

If only there is a way to go fully decat and still be legal!

Bluecat · Post by **Bluecat** » Tue Apr 25, 2017 2:57 pm

I am always very sceptical on emission testing equipment. I had a Porsche 996 C4S which failed the emissions test at Halfords. They suggested I take it to a Bosch garage to check which sensors were faulty or not working. I did this and was told absolutely no problem with the sensors which if there were would show up once the car was plugged in to a diagnostic machine. Bill was £55 for an mot compared with around £500 to replace sensors that were working fine. It seems a lot of garages have faulty equipment which give a lot of headaches to us car owners. Reported the garage to the MOT inspectors but heard nothing

MACK · Post by **MACK** » Tue Apr 25, 2017 3:13 pm

If it were me I would take it another garage and get them to test the emissions. At least that way you'll know if you have a genuine problem or not. Then go from there in terms of hunting down the problem. If it does turn out to be the Cats then at circa £2k I would be looking at used parts, its not like the Cats are known to fail so used replacements will hopefully be ok and no where near as pricey as new. Alternatively I would go down the route of seeing if any exhaust specialists can piece in new cats to the manifold, even if it means having them removed locally and couriered to the exhaust specialist.

Rufus59 · Post by **Rufus59** » Tue Apr 25, 2017 3:49 pm

RyanB88 wrote: ↑Mon Apr 24, 2017 11:52 am I don't think it'd be to do with the secondary cats as our engine can pass it's MOT with them removed (as long as they look like they're there visually!)

Has anyone been able to verify this?

RyanB88 · Post by **RyanB88** » Tue Apr 25, 2017 5:05 pm

Marc-j wrote: ↑Tue Apr 25, 2017 3:49 pm
RyanB88 wrote: ↑Mon Apr 24, 2017 11:52 am I don't think it'd be to do with the secondary cats as our engine can pass it's MOT with them removed (as long as they look like they're there visually!)
Has anyone been able to verify this?

Read the DLV thread for verification

Rufus59 · Post by **Rufus59** » Tue Apr 25, 2017 8:33 pm

I've seen it said in that thread before, but was wondering if anyone had actually passed an MOT without these two underfloor cats.

Mr Tidy · Post by **Mr Tidy** » Tue Apr 25, 2017 8:46 pm

Wow, this is almost turning into a Montego Blue Coupe thread.

Smartbear · Post by **Smartbear** » Tue Apr 25, 2017 9:23 pm

coupedan wrote: ↑Mon Apr 24, 2017 12:30 pm
RyanB88 wrote: ↑Mon Apr 24, 2017 11:52 am I don't think it'd be to do with the secondary cats as our engine can pass it's MOT with them removed (as long as they look like they're there visually!)
Ahh.. this was my worry as I know the primary cats are in the manifold - could be potentially costly me thinks!

Hi, with the mileage on your car this could easily be a sign of a failing ccv system.
Are you burning oil/have sooty tail pipes?
Rob

andyfanshawe · Post by **andyfanshawe** » Tue Apr 25, 2017 10:05 pm

HI coupedan.
Good to hear your car passed its MOT though.
Regarding the near threshold Lambda reading.

If you genuinely want to find out why the reading was close. and not speculate, find a garage who is conversant with the live data given from the O2 sensors, pre and post CAT. Also with short and long term fuel trims.

Shouldn't be too difficult to assess the performance of the various sensors.

i do an oxygen storage test, that involves sending the mixture rich and looking at how fast the o2 sensors react with an oscilloscope.

More accurately, how long it takes the post CAT sensor to drop lean when the rich mixture is removed, and compare it to the pre CAT sensor. This will accurately determine if any CAT is struggling.

Not cheap, but conclusive.

Alternatively, get a bottle of CATACLEAN and follow the instructions on it. Cost is about £15 and well worth it. Trust me on this.
If you don't believe me, or are skeptical, type in cataclean reviews and prepare to be amazed.

Additionally, make sure the oil and filter are changed regularly and as stated above, any crankcase ventilation systems are clean and clear.

Any slight exhaust leaks will also affect the lambda readings.

Hope all this helps!
An alternative to all this is to enjoy the car and worry about it next year!!

Andy.

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