UK MOT Emissions Failure

[Zino986]

Hi,
My 1998 Boxster 2.5 has failed the emissions part of the UK MOT test, but it was listed on the emissions report as a 2.7
Question is, would this make a difference to the parameters that it should be within?
The only thing it failed on is the CO reading (approx. 1.4%), the expected result max was 0.20%
It has a single O2 sensor, so I cant, (or don't know how to) check the operation of the cat.
Can anyone point me in the right direction?

By-the-way, it is used daily 50mls, not garaged, and have also used cataclean and 97ron fuel before the test.

Thanks in advance

[BYprodriver]

Big difference in allowable emissions between 97-99 & 2000 up Box here in CA due to the additional 2 converters. I don't know if UK is similar but worth looking into.

[thstone]

I doubt that the UK allowed CO emission level for a 1999 2.5L engine is substantially (if at all) different than that allowed for a 2000+ 2.7L engine - especially in light of the fact that your car (at 1.4%) was 700% over the allowable limit (0.20%).

High CO usually means that there is incompletely burned fuel in the exhaust. I am amazed that you don't have a CEL on!

Without a CEL to point us in the right direction, you'll have to check the fuel delivery system and fuel recovery systems along with the fuel/air mix control system.

[Zino986]

Hi, Thanks for your comments BYprodriver and thstone.

I am wondering if the system is on the change point of EOBD II and as there isn't a post-cat o2 sensor it won't put the CEL on as it doesn't know that there is a problem.

I agree, too much un-burnt fuel coming out of the exhaust, but is this manually adjustable?

What I really need is the figure for the UK MOT test results on a 98' MY 2.5 but I don't know where to find them.

[mikefocke]

I suggest boxa.net as a source for UK-oriented Boxster folks. The MOT issues are often discussed there.

Was the car well warmed up when the test was done? Always go in after at least a half hour drive.

[TeamOxford]

Originally Posted by mikefocke

I suggest boxa.net as a source for UK-oriented Boxster folks. The MOT issues are often discussed there.

Was the car well warmed up when the test was done? Always go in after at least a half hour drive.

+1. boxa.net is a great source for UK owners.

Plus, I would drive the bloody piss out of her before taking her in for MOT.

Just sayin'.......

TO

[thstone]

Originally Posted by Zino986

I am wondering if the system is on the change point of EOBD II and as there isn't a post-cat o2 sensor it won't put the CEL on as it doesn't know that there is a problem.

I agree, too much un-burnt fuel coming out of the exhaust, but is this manually adjustable?

The O2 sensor should know that there's a problem when the mix is so rich that you're 7 times over the emissions limit. Strange.

The air/fuel mixture is not manually adjustable. It is determined by the ECU based on inputs from the various engine sensors (MAF, air temp, throttle position, etc). The ECU will enrich the mix under certain circumstances.

If you have a Durametric, get a reading of the fuel trims, maybe that will tell us something.

[Zino986]

Thanks All.

Yes agree, the light should come on at 7 times the limit!
I have access to snapon diagnostics and although I can't go in to the specific vehicle with that, I can look through EOBD. I'll let you know what I find.

In the meantime I have asked the question on Boxa.net, thanks for the pointer.