Help....Failed MOT emissions!!

[SUBO2356]

just failed the MOT
CO levels were 8.05%vol...fail

CO(3.50) ....fail

1992 rev 2 turbo

Help AJS

[Andy K]

Check your lambda (oxy) sensor in the exhaust, there are a series of tests you can do to prove it's not working, it causes the engine to run open loop, where normally the ecu run closed loop, ie looks at exhaust O2 content and adjusts fuelling for lambda 1,
I wrote someting up for rev 3 cars, it's in the knowledge base,
cheers
Andy

[SUBO2356]

Cheers mate, i presume this is on the downpipe, do you know if it a one or two wire for the rev 2, as i may just replace it any way (not expensive)

cheers alan

[BenF]

The high CO you aren't burning all the fuel making it into the engine. I'd replace all the HT stuff - cap, HT leads, plugs (gapped to .8mm) and changing the O2 sensor won't hurt - a generic equivalent with a suitable plate for the Mk2s would be the job.

I'm assuming with CO2 figures that high you don't have a cat?

[SUBO2356]

Cheers,
just ordered a sensor, plugs are only 3000 miles old (iridiums)

will check the dizzy and leads

cheers again AJS

[screech]

the cat wouldn't make that much difference. my car put out 0.12 co when it was mot'd a week ago, and that's got no cat

[robertagar]

I had a similar problem. Check O2 sensor, if OK then weaken fuel/air mixture via adjusting screw on air flow meter.

Remove rubber bung and turn screw clockwise. Need to have a CO probe up the exhaust pipe and engine warmed up. I used a Gunson analyser, pretty crude but did the trick.

Perhaps tweaking the screw might cure the problem anyway. Mke a note o the existing position of the screw first in case you need to set it back.

This can be done at the MOT garage during the free retest.

Bob