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Update - CO Emissions - MOT Failure

T

TTX50

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Joined
5 Jan 2013
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Just failed the dreaded MOT on CO emissions on my 996 turbo. 0.63% vol when the max is 0.3%. Made sure the car was fully warmed up beforehand and the guys spent 30 minutes trying to get the readings to come down - same on both tailpipes. They had trouble last year, but managed it after about 20 minutes trying. The suspicion is failing cats in the aftermarket exhaust, but before I lay out a couple of grand on a new one (the cats are integral to the exhaust), does anyone have any ideas of other causes for the high CO - even though there's no CEL. Or any 'temporary' fixes I could try apart from 'buying the tester a pint'!
 
Re: CO Emissions - MOT Failure

TTX50 said:
Just failed the dreaded MOT on CO emissions on my 996 turbo. 0.63% vol when the max is 0.3%. Made sure the car was fully warmed up beforehand and the guys spent 30 minutes trying to get the readings to come down - same on both tailpipes. They had trouble last year, but managed it after about 20 minutes trying. The suspicion is failing cats in the aftermarket exhaust, but before I lay out a couple of grand on a new one (the cats are integral to the exhaust), does anyone have any ideas of other causes for the high CO - even though there's no CEL. Or any 'temporary' fixes I could try apart from 'buying the tester a pint'!
Click to expand...

Did they not have another car lying around that they could 'test'?
 
You don't necessarily have to change the while exhaust system just because the CATs have failed. I realise they're integral, but they can be cut off and new ones welded in place. Try ringing round a few exhaust fabricators to get am idea of cost - it should be significantly cheaper than buying a complete new exhaust!

The other thing is to make sure the CATs are as hot as possible prior to testing. Let the engine heat up, then give it some full throttle runs up and down a dual carriageway or somewhere before taking to the test centre. Just because the water is up to temperature on the dash doesn't mean the CATs are (or the oil, for that matter).
 
Re: CO Emissions - MOT Failure

chriscoates81 said:
Did they not have another car lying around that they could 'test'?
Click to expand...

:hand: I thought the same thing as my car always passes when my Indy puts it in after he services it :whistle:
 
eca02apc said:
You don't necessarily have to change the while exhaust system just because the CATs have failed. I realise they're integral, but they can be cut off and new ones welded in place. Try ringing round a few exhaust fabricators to get am idea of cost - it should be significantly cheaper than buying a complete new exhaust!

The other thing is to make sure the CATs are as hot as possible prior to testing. Let the engine heat up, then give it some full throttle runs up and down a dual carriageway or somewhere before taking to the test centre. Just because the water is up to temperature on the dash doesn't mean the CATs are (or the oil, for that matter).
Click to expand...

Thanks eca02apc. I'll try some local fabricators. The engine was fully warm and I did drive it at full tilt up and down a dual carriageway then asked them to do the emissions test first. It got so hot that it actually melted the probe on the test rig after 30 mins, which was when we decided to call it a day!
 
As I've no CEL or error codes, could there be any other reason for a high CO output? Or are there any tests an indy could perform to narrow down the problem? I really would like to know that replacing the cats will solve the problem before I go ahead. Thanks for the replies so far - I've googled for exhaust fabricators and come across some likely ones nearby and emailed them.
 
I used to have this problem and thought it was because of my remap or exhaust. I never had a check engine light. I did have a persistent DTC for secondary air but because it didn't trigger a cel I wasn't really concerned.

Anyway, the secondary air issue was only a relay that had dropped out. It is on the rear shelf and you need to remove the Bose sub to get at it. Once that was sorted the CO was spot on.

So, see if you have and codes stored. From memory it was 0411.
 
_gez_ said:
I used to have this problem and thought it was because of my remap or exhaust. I never had a check engine light. I did have a persistent DTC for secondary air but because it didn't trigger a cel I wasn't really concerned.

Anyway, the secondary air issue was only a relay that had dropped out. It is on the rear shelf and you need to remove the Bose sub to get at it. Once that was sorted the CO was spot on.

So, see if you have and codes stored. From memory it was 0411.
Click to expand...

Gez - thanks. I had a look, but unfortunately no codes stored. Would have loved it to be a simple fix like that. I'm going to clean the MAF with non-residue electronics cleaner, as there is a small amount of 'hunting' at startup and a very occasional misfire at constant lower speeds. It may help.
 
I would have the car checked by a specialist first. Engine is may be not running right......
 
TTX50 said:
_gez_ said:
I used to have this problem and thought it was because of my remap or exhaust. I never had a check engine light. I did have a persistent DTC for secondary air but because it didn't trigger a cel I wasn't really concerned.

Anyway, the secondary air issue was only a relay that had dropped out. It is on the rear shelf and you need to remove the Bose sub to get at it. Once that was sorted the CO was spot on.

So, see if you have and codes stored. From memory it was 0411.
Click to expand...

Gez - thanks. I had a look, but unfortunately no codes stored. Would have loved it to be a simple fix like that. I'm going to clean the MAF with non-residue electronics cleaner, as there is a small amount of 'hunting' at startup and a very occasional misfire at constant lower speeds. It may help.
Click to expand...

What did you use to read codes? Please don't say a generic OBDII reader! If you used a durametric then fair enough, pity it wasn't an easy fix.
 
_gez_ said:
What did you use to read codes? Please don't say a generic OBDII reader! If you used a durametric then fair enough, pity it wasn't an easy fix.
Click to expand...

I'm going to disappoint you and say I used a generic OBDII reader! Looks like it's time for a visit to an indie then. Thanks for the tip - I'm guessing from this that the generic units don't pick up all the Porsche codes?
 
Normally if the CATs are that far gone they'll be triggering a fault code from the lambda sensors about CAT inefficiency. It's possible it's something other than the exhaust, i.e. the engine running rich. That being the case, you can check for mixture adaptation values (fuel trims), but you'll need Durametric or similar.

Possible causes for rich running: faulty pre-CAT lambda sensor; faulty MAF etc. again, can be investigated using a quality code reader to avoid 'shotgun maintenance' replacing everything until the problem goes away.
 
Exactly 8)
 
Make sure the tester shoves the probe right around the sharp bend of the exhaust. Last year mine struggled for 15 minutes revving at 3000. In fact it never made it. This year it passed within a minute with a fully inserted probe.
 
KeithL said:
Make sure the tester shoves the probe right around the sharp bend of the exhaust. Last year mine struggled for 15 minutes revving at 3000. In fact it never made it. This year it passed within a minute with a fully inserted probe.
Click to expand...
I watched him do it and he definitely shoved it round the bend. Hence the melting probe issue! I've cleaned the MAF today which made a noticeable difference to the idle and throttle response and am going to get the emissions tested again on Monday. If it's still the same, then it's off to Nine Excellence for some detailed diagnosis.
 
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