Failed MOT Today

[GOOFY]

Hi

My Boxster 2.5 24k , failed MOT today due to high (co?) emissions. The tester with some experience of Boxsters stated it could be 3 things:

1. Lambda failure - said he could get these for £80
2. "U" clamp from catalyst to exhaust leaking .
3. Catalyst failure - he had just changed a set on a Boxster (which he duly showed me!)


In trying to work out the best course of action I assumed the following:

1. if the lambda had failed would this not show up as a (engine) warning light ? And should I get diagnosis from OPC to confirm ?

2. The "U" clamps were indeed leaking as these were removed and re-installed after some heavy chisseling which have put them out of shape. Secondly the exhaust fitted is one of those similar to the PSE , with the bypass pipes around the silencer. Can this really affect the emmission readout ? I have also fitted an induction kit and foam air filter and have always experienced a mild flat spot in mid range before 4000 rom. Is this connected as well ?

3. Any way of knowing for sure if it is the catalyst ?

Any advice would be most welcome - as I have 10 days to figure this out !![8|]

 

[Black80XSA]

Those modded exhausts bypasses part of the catalyst from reollection, so that won't help !

Also your low mileage suggests the whole system needs a damn good thrashing to blow the crap out - never take the car for an MOT without a good thrash first.

 

[JCB..]

Very unlikely for the cat to have gone after 24k.

I would wager it's the tinkering that's spannered it.

 

[malax911]

Working at the greek MOT all these years (3[]) never heard of a porsche failing MOT but then again we dont have many porsches here!! Plenty of Boxsters though...
A possible λ failure would 90% cause your engine to work "rich" ( λ well below 0,970). If that happens for a long period of time the catalyst goes out...
Exhaust leaking could affect (increase over the 1,030 limit) the λ values but rarely cause high co emissions...
How high exactly are your co emissions? How is the λ values? Is the car failing co emissions on both idle and increased revs?
No thrashing is required IMHO. A good 3-4 full throttle openings should be enough for any porsche of that mileage...

 

[Richard_Hamilton]

The silencer bypass pipes wouldn't affect emissions. They do that - just bypass the silencer, in the same way as a genuine PSE. They don't bypass the cat. I'd get a check done to get the lambda outputs and see if they are working properly. If they aren't, it will throw the emissions out of range, and you won't necessarily get a CEL. Find a good indy and they should be able to sort it out reasonably cheaply.

 

[GOOFY]

Hi thanks for the advice.

Failed on fast idle and Second fast idle Lamda only reading 1.081 vs max 1.030 !

CO and HC well within limits.

Further research leads me to believe it is the post catalyst connect to the exhaust leaking - the couplings. I also spotted this on JZ Maytech website as a problem with Boxsters MOT failure (although when I spoke to them they seemed unaware of this issue!).

Taken from another site:
Quote:"If the fault is a high lambda reading, with a high O2 reading but with normal CO and HC readings, the most common cause is post combustion air leaks. A small exhaust system air leak will leak air into the exhaust before any blows can be detected. Only a small volume of clean air introduced into the exhaust will cause a car to fail the MOT test. " .

So I'm going to change the couplings first .

 

[malax911]

CO and HC well within limits? Then its the exhaust leakage causing your problems.
If fast idle and 2nd fast failed at 1,081 why didnt the tester raise 500rpm to help you pass then?You were very close...

 

[David W.]

"have many porsches here!! Plenty of Boxsters though... "
Oi steady [&:]
DW

 

[malax911]

ORIGINAL: David W.

"have many porsches here!! Plenty of Boxsters though... "
Oi steady [&:]
DW

Oooops!This is the boxster forum right?
I meant that there are very few porsches and when you finally come across one it is usually o boxster (like mine [])!

 

[sailor]

What a diplomat!
Well done, that man.

JohnC
993turbo

 

[Glyn]

The flat spot with the CO problem seems to suggest the MAF.


Glyn

 

[GOOFY]

Success today ! And with nothing more than exhaust paste on the flanges of the exhaust clamps !

Went along to my friendly local mechanic armed with my new clamps to fit. He also runs an MOT station (I wished I had tried him first, but for convenience went to the 1st place due to proximity to work). Anyway in his experience of Porsches he said they are "solid" and after what I told him about the air leaks that may cause a high lambda reading he duly applied paste around the clamps ends. (Porsche recommend they are replaced and never re-used - advice I should have taken !). Fired it up took some readings and all was well - 1.03 ! He did say that because of the compact exhaust arrangement it was quite sensitive to leaks and the PSE type bypass exhaust can make a difference.

Thanks all for all advice from the replies. I am dissapointed with some of the well known independents who I had rung round - none seemed aware of the above as a possibility but I suppose they were cautious. So before you replace your cat or lambda check the three readings : if only the lambda is high (O2) then exhaust leakage is a possibility.

I shall nevertheless be cleaning out the MAF and checking all intake manifold connections soon .

[]

PS . The garage is JP Motor Company , Mitcham , Surrey . 0208 640 2124. They specialise in Rolls Royce, Jaguar, Bentley - especially classic cars. (Had a lovely v12 Jaguar E_Type in Ferrari red !).