Failed MOT, high CO

[Robert986]

Originally Posted by pilot4fn

Hi Robert,
I have similar set-up, but on 2.7 engine (with manual).

As I installed the long tail headers and downpipes with 200 CPI cats - the car run pretty nice compared to old OEM exhaust.
On getting ready for MOT, I swapped new Bosh spark plugs (with 4 leads each but non platinum). Car run a tiny bit rough as of what I could feel.
Went to the MOT and failed due to too high CO%.
Also the CAT efficiency CEL showed up couple of times a week. So I swapped also all Lambdas. Car still did run a bit rough.
Next I installed new and NGK Platinum spark plugs (NGK BKR6EQUP). Now the car run very nice.
Cleared the CEL's with Durametric and went to MOT.
The inspector looked at the exhaust after I told him what I had done to improve the CO%.
Initial test was again too high CO%, but then he heated the CAT's real well for 5 minutes on approximately 2500rpm and then the car had CO% on 0,08!!!

Reasoning he told was that the 200 CPI 'race cats' are metal based and required more heat to operate than ceramic CATs (he said that he has same style 200 CPI metal CATs on his Impreza...).
For next MOT he told to drive the car for 10 minutes with very high rpm (actually told to drive against the rev limiter ) immediately before the MOT to get the CATs very hot. Then the CO% should clear easily.

Anyhow, I'm planning to take my car to same inspector also on the following years to come

Thanks a lot, great input!

I did heat the cat:s quite a lot before MOT, when it failed I got a chance to heat them more and went for a 20 min very VERY spirited drive.. Still the same values at 2500rpm, 0,7 on bank-1 0,5 on bank-2.

So I have a feeling there is another bug somewhere..

I now also checked the old exhaust pipes to see if the right side (bank-1) had a lot of soot.. None.. Both pipes where super clean. This tells me that it shouldn´t be a major problem with the engine, like major leaks in the cylinders.

Idea-1 -Can it be that the gaskets provided with the ebay-headers are of low quality so there is a small air-leak before the pre-cat O2 sensor, thus giving a slight rich condition? (however lambda after cats tells different) Would a slightly rich condition pre cat be mitigated by the cat to give a good lambda in the tailpipe?

Idea-2 -Could it be a leak in the AOS, so I get a lot of oil residue in the intake? Will check that tomorrow. Spent today with cleaning up in the garage to give room for further examinations.

[pilot4fn]

Originally Posted by Robert986

Thanks a lot, great input!

I did heat the cat:s quite a lot before MOT, when it failed I got a chance to heat them more and went for a 20 min very VERY spirited drive.. Still the same values at 2500rpm, 0,7 on bank-1 0,5 on bank-2.

So I have a feeling there is another bug somewhere..


Idea-1 -Can it be that the gaskets provided with the ebay-headers are of low quality so there is a small air-leak before the pre-cat O2 sensor, thus giving a slight rich condition? (however lambda after cats tells different) Would a slightly rich condition pre cat be mitigated by the cat to give a good lambda in the tailpipe?

Idea-2 -Could it be a leak in the AOS, so I get a lot of oil residue in the intake? Will check that tomorrow. Spent today with cleaning up in the garage to give room for further examinations.

I'd believe that both ideas you mention are feasible.
Easier to check first is the AOS failure. As the engine is warm and idles, open up the oil cap in the trunk. If it has a very high vacuum (I guess hard to lift the cap), then you'll have most likely a failed AOS.
Also, the inteke plenums would have oil inside if AOS has failed.

[Robert986]

Ok, first we look at the AOS..

I did the oil-cap-test.

It really felt easy to open the oil cap, no powerful vacuum at all, but I realize this is totally subjective since I have no vacuum meter.


I then went on and popped the plenum & throttle body. I must say, there is some oil in there, but is it normal levels? As you see my finger get quite soaked when I scrape the inside of the plenum, I don´t see a lot of oil in the actual manifold. at least not a lake.. ;-)

So, does this mean that my AOS is not up to the job? Should I change it? I have been tracking with R-compounds, but not since last year, so I cannot imagine the oil beeing that old.

As you can see the throttle body was kind of dirty as well, cleaned this up.

[pilot4fn]

I had similar amount of oil in my plenum as I opened it on the spring this year while cleanign the throttle body which also looked like yours. Clened also the plenum and drove for a couple of weeks and then one morning the AOS died with a large puff of white cloud
This could mean that also your AOS is on a way out - somebody more knowledgable could chime in on that.

[Robert986]

Originally Posted by pilot4fn

I had similar amount of oil in my plenum as I opened it on the spring this year while cleanign the throttle body which also looked like yours. Clened also the plenum and drove for a couple of weeks and then one morning the AOS died with a large puff of white cloud
This could mean that also your AOS is on a way out - somebody more knowledgable could chime in on that.

Thanks for input, I guess it cannot hurt to change the AOS, just more work..

[Robert986]

Update:

Switched AOS, MAF, o2-sensors & spark plugs, still no luck.. Then I put back the oem cats, instead of the cheap eBay ones. o2 and HC back on zero again!

Anyone else had bad luck with eBay cats?

[pilot4fn]

Originally Posted by Robert986

Update:

Switched AOS, MAF, o2-sensors & spark plugs, still no luck.. Then I put back the oem cats, instead of the cheap eBay ones. o2 and HC back on zero again!

Anyone else had bad luck with eBay cats?

I had similar issues with 200 CPI cats. On this thread at the answer #2 is the reasons for the issues and how the MOT was cleared.