CO check without gas analyzer

[Nick Triesch]

Two years ago my 85 911 passed California smog but just made it with CO readings. So today I got a 3mm allen and turned the CO adjustment screw counter clockwise about 1/8 tun to lean out the mixture just a bit. Had car smogged today and CO was dialed in! At 0.34. Max is 0.65. My point is you always don’t need a gas analyzer. Well known Porsche mechanic in San Diego told me a good way to check CO is by the California smog test unit. Anyway, my car passed with good results. Other things I did was I used 97 octane gas for the test, 40 pounds of air in rear tires for less drag and fresh oil.

[proporsche]

back in the 70`s in Czechoslovakia we did not have any fancy analysers..we simple used a match-flame in the rear of the muffler pipe...if the flame went in it was lean -just about ok ..if the flame went away from the pipe it was too rich..All adjustments were done by feel and sounds after..

Ivan

[fanaudical]

Congrats on getting through! It took me 8 tries last time I had to get through Oregon DEQ.

There are lots of threads here about how to tune CIS without a gas analyzer. I finally installed a wide-band O2 gauge on mine last year and it helped me find several issues - a worthwhile investment.

My grandfather showed me the match flame trick many years ago on his AMC - I had forgotten about that one. Thanks for the reminder.

[Nick Triesch]

Old time tricks! A few years ago my car was missing horrible. The old school mechanic got a simple piece of paper and put on near the exhaust while the car was running. He said air was getting in the engine because the paper wanted to suck in. He was correct because cylinder number sucked in the intake gasket!!! Old tricks work! Also there is the dime on the hood not moving when car is tuned up nice!

[proporsche]

Originally Posted by Nick Triesch

Old time tricks! A few years ago my car was missing horrible. The old school mechanic got a simple piece of paper and put on near the exhaust while the car was running. He said air was getting in the engine because the paper wanted to suck in. He was correct because cylinder number sucked in the intake gasket!!! Old tricks work! Also there is the dime on the hood not moving when car is tuned up nice!

back in the 1980 when i to balance the front wheel i used glass of water..when done properly the water would not move..;-)

Ivan
we were using the spin rotor kinda wheel balancer with the wheel on the car.forgot the name of it..this one

[Glenfield]

This thread should help you. Correlates CO with AFR. May be easier to get a hold of an AFR to proxy your CO. Could also do it by measuring duty cycle but I’ve never been able to get a good read on that

https://forums.pelicanparts.com/porsche-911-technical-forum/1003338-co-meter-2.html

[dannobee]

Ivan, was that an Alemite balancer? We had one of those when I was an apprentice.

Checking the CO *should* be done before the catalyst. A working cat will clean up the CO enough for it to blow zeros on the Smog Machine.

[proporsche]

dann..yes ,just like the one on the picture;-) it was actually fun job to do ,very satisfying;-)

Ivan

[Nick Triesch]

Why should the co be checked before catalyst? I slightly changed my co setting to less rich and now it is perfect on California smog check reading. Also, the numbers that count are the ones from the completed smog check.

[dannobee]

Ummm...because that's how the shop manual says it should be done? Even the emissions label says to check it that way.

Actually, if the catalyst is brand new, you could be pig rich and the catalyst will clean it up significantly, until it can't. Measuring CO post catalyst isn't the correct way to do it.

I was a smog tech for over 30 years, I kinda know a little bit about how it works.

[Nick Triesch]

Not a good enough answer. I was able to bring down my co with a slight turn of the adjustment screw. My 85 Carrera passed much better than before. Like I said , what the machine tester says at the smog check is what counts. I guess I could have gone to a shop , paid money to have the co checked with a gas analyzer.

[proporsche]

Nick..what Dann tried to tell you.The correct way is to check prior cat.If you look down there is a 13mm head bolt where the sniff-pipe should be connected.If your CAT is ok it will correct whatever you are doing.......so saying that it might have passed the smog prior your adjustments....either way you got it ......

[AndrewCologne]

Originally Posted by Glenfield

This thread should help you. Correlates CO with AFR. May be easier to get a hold of an AFR to proxy your CO. Could also do it by measuring duty cycle but I’ve never been able to get a good read on that

https://forums.pelicanparts.com/porsche-911-technical-forum/1003338-co-meter-2.html

Dont know from where those listings are coming from, saying that an AFR of 14.7:1 (means Lambda 1 with gas coming with no ethanol) does result in a CO of 0.0 or 0.1.

With a 3.0 engine at AFR 14.7:1 before combustion, a typical CO result with no cat at the tailpipe is approx. 1-1.2%.
And even here it depends on the exhaust system which could mess up AFR readings. in case of a system using SSI HE's where only one exhaust flow from one side is being measured by the sensor, at least at idle the readings will be off, due to significant less heat and less flow volumen at the sensor compared to an original factory setup where the flow from both sides will be collected and measured before a cat wehre in that area much more heat is present for optimal resulting readings.

https://nineelevenheaven-wordpress-com.translate.goog/abgasregelung-beim-sc/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp
(A link via Google translator, manual translation into english language will follw.)
See i.E. in the article the calibrated CO measure device at the german DEKRA station, ... even there with a Lambda of 1.035 wich correspondens to an even higher AFR the CO results in 0.73.