tuning with gas analyzer

[sheldon j]

good day all. Does anyone one have experience with tuning using 5 gas analyzer and specs for co at idle and at speed, my car 70 280sl failed smog and im trying to pass the test.

[stickandrudderman]

you only need to measure Co and HC.
Co is a product of combustion and HC is unburnt fuel.
So, if 1 spark plug is not working your HC will be high because the fuel that is being injected is not being ignited but your co may be within limits because that fuel which is being burnt by the other 5 cylinders is still creating Carbon Monoxide.
ideally Co should be around 4 to 4.5% at idle but you might have to go as high as 7% to achieve smotth running (although this would be indicative of some other fault such as poor spray pattern).
HC could be as low as 250 or as high as 600 according to engine condition.
Any higher than that and you should be looking for a reason. (fuel contaminated engine oil from a failed injection pump always leads to high HC).

[rwmastel]

Sheldon,

Hello and welcome to the Group!  I see it's your first post.  I'm sure you'll get a lot of good help here, but you can also help yourself using our Search feature.  While in this Drive Train forum, search for "gas analyzer" and find past discussion threads about the topic.  Happy reading and I hope your car passes next test!

[ctaylor738]

I've used my Gunson's Gastester for years to measure idle CO. It works OK for CO readings above 2%.

Late cars are complicated because the emissions system that uses vacuum to change the timing is probably not working.  To reduce the CO, I suggest you retard the timing to at least 2 degrees ATDC, more if the car will still idle, increase the idle air, and lean out the idle adjuster on the back of the pump. Do this in stages until you get the CO to where it will pass inspection. The car will run poorly at low rpm, but you should be able to limp to the inspection station.

Then you can reset the timing and mixture until the next test.

Cheers,

CT

[mauro12]

What is the value to pass the co inspection ?

[ctaylor738]

The 280 I was working on is registered in Washington DC.  The requirement is 10% CO at an idle speed less than 1200 rpm.

CT