CO & HC emissions levels advice needed

[peanut]

my local village MOT station is like a trip back into the 1930's [] The MOT is done over a pit in the floor ...I kid you not []

My 89 944S2 has passed everything except the CO emissions. ! Its now failed twice in a week and the second test was even worse than the first!.

I had to beg for a printout and it doesn't give me much information about emissions requirements . can someone please tell me what the CO emissions should be for a 89 944S2 ?
All the test result printout says is
1st test CO% .............Max Limit 3.500 Actual value 4.372 HC max limit 1200ppm.......... Actual 308ppm
2nd test CO% ............Max Limit 3.500 Actual value 6.388

3.500 what ? cornflakes ? centimetres ?

 

[scam75]

% CO to air and % HC to air I would think? Not an expert on the S2 but I would think your AFM would be the culprit here. There is an adjuster screw on it I think or else it may have track damage. There are many write ups on moving the tracks which may help. Also giving the car a good, lengthy blast for half an hour or so before the test should see your numbers head back down the scale a bit, how much may depend on the condition of your AFM.

Stuart

 

[peanut]

well its apparently % volume of carbon monoxide and PPM (parts per million) Volume of hydrocarbons but in relation to fuel or air Ive no idea .

What I need is the threshold range thats applicable to my car and the units of measurement . I can't find any reference to it anywhere on line not even VOSA or DVLA

thanks for the suggestion scam.

i'll be checking the AFM and everything to do with over fueling

 

[Mikebarry202]

CO is % (incorrect air/fuel ratio), HC is parts per million (ppm) (un-burnt fuel). Pass rates copied from a website are below:
Carbon Monoxide Emissions
For vehicles registered between 1st August 1975 and 31st July 1986, the CO level must not exceed 4.5% by volume.
For vehicles registered between 1st August 1986 and 31st July 1992, the CO level must not exceed 3.5% by volume.
Hydrocarbon Emissions
For vehicles registered between 1st August 1975 and 31st July 1992, the HC emissions must not exceed 1200 ppm (parts per million).

The reasons for failing with high CO readings will relate to the fueling side of things, not the ignition side (plugs etc). As mentioned, the AFM a likely culprit.....

 

[peanut]

thank you Mike thats just what I needed.
I looked for 2x hours and couldn't find the relevant emissions requirements for my age of car anywhere.

 

[garyadams]

I was once told that the best time to replace your car's oil and filter is just before the MOT as the old oil is dirty and this can also contribute towards high CO emissions. Also agree with the AFM being a likely cause but what about your air filter? when was that last changed.

Gary

 

[wolfie308]

John..for reference, I just checked my last MOT and the values were CO - 0.67% and HC - 140 ppm.

Out of interest, what were your HC readings? Sorry I can't be any help with suggestions.

Oh.....and that's with a decat pipe fitted

 

[peanut]

thanks for your suggestions chaps .

Wolfie my HC result is at the top. 308ppm with a maximum of 1200ppm
its the CO it failed on

 

[wolfie308]

I realise it was the CO that was the issue, I just wondered how your HC reading compared as you didn't mention a value in your original post.

 

[peanut]

my sincere apologies Wolfie.

You're quite right ....another senior moment []

Anyway they are well within limits at 308ppm
The issue is obviously an over-fuel issue whether too much fuel or too little air wasn't apparent yesterday but I've just removed and checked the air filter and it was half blocked by nut husks and other detritus so I suspect a new air filter will bring the CO% down to within limits hopefully

I've still got to check the 02 Lambda and its connection as the MOT tester used a big screwdriver to prod around everywhere and could have damaged it.
I'll change the Lambda anyway as its so cheap its not worth keeping it .I know it has to be at least 12 years old as was the air filter ..ahem....cough

Well at least we now know where Squirrel Nutkin has been squirreling his nuts don't we !

 

[IanK]

My S2 failed its last MOT on emissions - the CO was around 6% I think. My local Indie cleaned and "recalibrated" the AFM and it was down to 1% on the retest.

Ian

 

[peanut]

thanks Ian yes the AFM is on the list for sure but there are lots of other things to check too .
I was looking back through my documents folder and realised the car hasn't been serviced for 5 years ! Its only been driven 500 miles in that time !

I'll do a full service whilst i'm there []

Looking at the state of the air filter today the chances are that a new filter will improve things no end.
I'll also be checking the vacuum system for leaks and the cold start mechanism, engine temperature sensor etc

 

[Waylander]

that's a K&N air filter can be washed out and re-oiled, the Lambda sensor is a real nightmare to remove they normally chew the threads on the way out, they should be replaced every 60k according to the workshop manual.

for M44.41 and M44.11/12 Engines
Don't buy a cheap one they don't react fast enough, genuine Porsche (Bosch) 944 606 135 02 @ £143.00, or the Bosch one 0 258 003 011 @ £70.00 ish

 

[peanut]

thanks waylander yes that was lucky it was a K&N . I was just about to order a new disposable filter.
Thanks for the tip about the cheap Lambdas I'm not even sure if my S2 has one fitted and if it did where I'd find it.