What pollution?

[s3swiss]

Just passed the MOT with my 1990 S3 - CO %vol = 0.190 (max limit 3.5) and Hydrocarbons 78 (max limit 1200) - apparently cleaner than some cat-equipped cars! Are these readings about average for the 2.9i?

[tvrgit]

Can't specifically remember mine but the guy did say that the emission readings were remarkably low and he asked if I had doctored it somehow. I said no, that was as it runs all the time.

I think that the numerous leaks in one side of the exhaust (now fixed) probably helped as well though!

[GreenV8S]

s3swiss said:

Are these readings about average for the 2.9i?

Probably about average for a 2.9i that is switched off.

[s3swiss]

say no more - hopefully there will always be a few 'nice' MOT testers around!

[Jed-S]

The CO reading on mine was 0.94% and HC was 73ppm. That's a 91 S3 with 91k on the clock.

Looking at the Haynes manual for the 2.9 Sierra the idle CO is listed as 0.75%+-0.25%. This makes me think you might be running a bit lean - possibly some air leaks somewhere?

[F908 Tim]

I remember mine was dead on 0.80 which the MOT guy was impressed with, cant remember the Hydrocarbons result...will have a look now out of interest.

[s3swiss]

Used a Gunsons CO meter before the MOT and got about 2% but it reckons it could be up to 2% in error! Just had a look at my timing the other day and using a strobe it was showing about 15deg BTDC. This was after I'd removed the dizzy for a head-gasket change and reset it to the tell-tale mark I'd made on the casing. Moved the timing to nearer 3-5deg BTDC as per the Bible but not had a chance to road-test it yet. Revving it with no load seems to give a few more pops and bangs on over-run than before. Might even stick it in my Ford garage for a proper timing/mixture set-up (assuming they still have the diagnostic kit for the 2.9 V6 these days!)