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Capitalist and Patriot
 
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CO2, 02, HC & CO% what do they really mean?

Fellow pelicans

I have a smog check coming up in a couple of months and wanted to make sure my 81 911 SC is in proper tune. Among the usual things such as properly warmed up, plugs, cap & rotor in good health etc. I was wondering if you might help me gain the most knowledge of the current state of tune from my last smog check emission numbers?

Also, wasn't there a way of using this data to understand my A/F ratios? I've always felt that the smog setup was a bit on the lean side...

Here goes:

Co2 (%)
Idle: 14.10
2500 rpm 14.30

02 (%)
Idle: 0.90
2500 rpm 0.50

HC {Max allowed: Idle 120, 2500 rpm 150}
Idle: Avg 42
Measured 16
2500 rpm: Avg 37
measured 29

CO (%) {Max allowed: Idle 1.50, 2500rpm 1.50}
Idle: 0.10
Measured: 0.01
2500 rpm
Avg. 0.20
measured: 0.15


It passes and over the last 8 years it has always been, with a little timing and mixture adjustments, pretty close to these #'s...

I've had techs tell me how surprised they were by how clean this engine runs, but is it too lean? I leg it all the time, cuz it's good for it!


Are the Co2 % my A/F ratios?


Any interpretations of these numbers would be very helpful and as always thanks Pelicans!
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Old 04-02-2010, 05:41 PM
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this may help..
Vehicle emissions control - Wikipedia, the free encyclopedia
and this..
Air-fuel ratio - Wikipedia, the free encyclopedia

those readings dont tell you specific AFR's but they are related in a sense, as if you had incorrect ratios, you readings will change one way or another. If everything is normal, then you pass the test..
Old 04-02-2010, 06:32 PM
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I guess as I'm within parameters means there's not much else to decipher from these numbers regarding how well my fuel and exhaust system is working.....

I was hoping for a few indicators that would lead to metrics we (CIS owners) could use to better tune our systems before and after smog checks.

Guess it just isn't possible with this system....

Oh well

Thanks for the link Rattlesnake
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"Dream it, Believe it, Decide it, DO it "
Old 04-02-2010, 07:01 PM
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You are running very close to Stoichiometric as evidenced by the low CO and O2 readings. You can get a bit more power by richening the mixture (CO at 1.5%)
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Old 04-02-2010, 09:08 PM
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Quote:
Originally Posted by HarryD View Post
You are running very close to Stoichiometric as evidenced by the low CO and O2 readings. You can get a bit more power by richening the mixture (CO at 1.5%)
Thanks HarryD!

This is more of what I was looking for

A little more on Stoichiometric here:

Stoichiometry - Wikipedia, the free encyclopedia

Stoichiometry (sometimes called reaction stoichiometry to distinguish it from composition stoichiometry) is the calculation of quantitative (measurable) relationships of the reactants and products in a balanced chemical reaction. It can be used to calculate quantities such as the amount of products that can be produced with given reactants and percent yield (the percentage of the given reactant that is made into the product).

The stoichiometric coefficient νi represents the degree to which a chemical species participates in a reaction. The convention is to assign negative coefficients to reactants (which are consumed) and positive ones to products. However, any reaction may be viewed as "going" in the reverse direction, and all the coefficients then change sign (as does the free energy). Whether a reaction actually will go in the arbitrarily-selected forward direction or not depends on the amounts of the substances present at any given time, which determines the kinetics and thermodynamics, i.e., whether equilibrium lies to the right or the left (how lean or rich my system is set, right?)

If one contemplates actual reaction mechanisms, stoichiometric coefficients will always be integers, since elementary reactions always involve whole molecules. If one uses a composite representation of an "overall" reaction, some may be rational fractions. There are often chemical species present that do not participate in a reaction; their stoichiometric coefficients are therefore zero. Any chemical species that is regenerated, such as a catalyst, also has a stoichiometric coefficient of zero.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Ok, so.....

From what I gather at first blush Stoichiometric is essentially a chemical 4D imaging and measuring tool? ...or the formula used to describe the quantitative relationships, in this case CIS; the fuel injection, combustion, O2 neuro system working together, calculating the relationship the CIS neuro system interacts with air, fuel, spark, A/F rations etc. cause and effect....cause and effect...
Did I get that right?

Which metric from my initial emission data did you use?

Fun stuff!!!
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'81 911SC RoW Targa (lot's of goodies)
'07 Lexus IS 250
'84 633 csi (turbo charged-sold)
'68 912 Targa (sold)
"Dream it, Believe it, Decide it, DO it "
Old 04-03-2010, 11:05 AM
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Don't make it complicated. In the most simple terms Stoichiometric means that you use up all of your reactants to make the products.

From high school chemistry we know that:

(x parts reactant A) plus (y parts reactant B) gets you (z parts product)

As an example:

1 O2 + 2 H2 == > 2 H2O
(or you need one part oxygen gas plus one part hydrogen gas to make 2 parts of water)

In the case of gasoline in air, it is more complicated. Gasoline is a hydrocarbon containing Carbon and Hydrogen.

If you burn the fuel (gasoline with 100% perfection i.e. at Stoichiometric), you will convert the gasoline to water (H2O) and carbon dioxide (CO2). The reaction has two steps that are something like this:

CxHy + zO2 ==> xCO + 1/2yH2O + aO2 (left over when you make CO or H2O)
xCO + aO2 ==> bCO2 (you then use up the remaining O2 to convert the CO to CO2)

Overall Stoichiometric reaction is:

CxHy + zO2 ==> x CO2 + 1/2yH2O

If you are too rich (i.e. not enough O2), the overall reaction looks like htis:

CxHy + zO2 ==> aCO + bCO2 + 1/2yH2O
(where a+b=x)

If you are too lean (i.e. too much O2), the overall reaction looks like this:

CxHy + zO2 ==> xCO2 + 1/2yH2O + ?O2
------------------------------------------------------------------------------------------

Too rich or lean is noted by looking only at the CO reading. High CO, too rich, low or 0 CO, too lean.

---------------------------------------------------------------
Some other combustion information. If you are lean, the temperature in the cylinder is higher than desired but your mileage is better. A lean mixture also leads to the formation of NOx and can cause mechanical damage to your cylinders due to the excessive heat.

Converserly, a rich mixture, cools your cylinders and since you have all the fuel you needs, you make the most power. The downside is reduced mileage and higher emissions of HC's.

Also, the HC should go down as the CO/CO2 goes up.

NOx is a side reaction of the nitrogen in the air reacting with some of the O2 as well. NOx formation is driven by temperature (higher temperature, more NOx).

The air regulators care mostly about NOx and HC as these react in the air form ozone (O3). They use the CO, CO2 and O2 to determine if your car is running in the correct operating mixture to reduce the formation of CO and NOx.

Does that help any?
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Old 04-03-2010, 12:14 PM
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Here's a little more info; an excerpt from my new book which is now at the publisher...

Once again, emission control requirements take center stage, not only did they send the mighty Turbo packing, a new development for the 911 SC is probably the highlight for 1980. It’s amazing how quickly emission control devices moved from an almost afterthought status to an engineering challenge that played a part in almost every engineering decision. Porsche, often at the forefront of automobile development, installed a three-way catalytic converter fitted with an oxygen sensor on all ’80 SCs. Chemistry was never one of my strong points, but, basically, a three-way catalyst has three jobs:

1. Carbon monoxide (CO) is considered a toxic, non-greenhouse gas. The 3-way cat will cause oxidation of that gas to the less harmful greenhouse gas, carbon dioxide.

2. Hydrocarbons (HC) are unburned, carcinogenic compounds made of carbon and hydrogen. The 3-way cat will cause oxidation of those compounds to carbon dioxide and water.

3. Nitrogen oxides (NOx) are a combination of nitrogen dioxide and nitric oxide, both are poisonous gases. The 3-way cat will cause a reduction of those gases to nitrogen and oxygen.

The three-way catalytic converter replaced the already in-use two-way cat, which would be ineffective in reducing NOx emissions to meet regulatory changes for the 1981 model year. Enter the stoichiometric point, the theoretical point at which combustion is complete. In other words, all the carbon (C) is burned to become CO2, all of the hydrogen (H) is burned to become H2O, etc. The 3-way cat works best when it receives exhaust from an engine that is running slightly lean, above the stoichiometric (ideal) point, which is between 14.8 and 14.9 parts air to 1 part fuel.

When more than the required amount of oxygen exists the engine is running “lean,” which favors the above two oxidizing reactions. When excessive fuel is present the engine is running “rich,” at which point the cat favors the reduction of NOx.

Enter the oxygen sensor. Originally called Lambdasonde by its developer, Bosch, it is a sensor probe that installs into the exhaust just before the catalytic converter. The oxygen sensor measures the remaining oxygen content in the exhaust, and then sends corresponding signals to an electronic control unit (ECU). The ECU is then able to make fine adjustments to fuel delivery, and keep the fuel injection system as near as possible to the ideal stoichiometric point.

Porsche’s use of the 3-way cat and Lambda was so effective that for the first time since 1975 no smog pump (auxiliary air injection) was required. That alone did wonders for the engine compartment’s appearance, as well as improving access to some service related parts such as the ignition distributor. In addition, exhaust gas recirculation (EGR) was also eliminated.
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Old 04-03-2010, 01:57 PM
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From the megasquirt manual on emmisions tuning:

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Old 04-03-2010, 02:31 PM
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FANTASTIC GENTLEMAN!

This is very helpful as I'm trying to not only keep the proper tune of the CIS, emissions etc but also create a baseline for a system that isn't designed with a motronic type ecu. All of this information will assist in this objective.

Keep it coming as I'm sure there are others who will benefit from this information in one thread...

Cheers, Jason
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Last edited by 911Freak; 04-03-2010 at 11:22 PM..
Old 04-03-2010, 02:49 PM
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also, as a diagnostic tip, don't think of 'too rich' as too much fuel, you have to think of it as not enough oxygen... The Oxygen sensor doesn't sense fuel, only oxygen..
Old 04-03-2010, 02:52 PM
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And to pile on to Pete's note, an additional thought:

EGR is used to reduce the peak temperature in the cylinder which helps to reduce NOx formation. Since the exhaust gas is "used up", it acts like an inert gas to reduce the amount of fuel and air is introduced into the cylinder.
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Old 04-03-2010, 09:36 PM
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Quote:
Originally Posted by HarryD View Post
And to pile on to Pete's note, an additional thought:

EGR is used to reduce the peak temperature in the cylinder which helps to reduce NOx formation. Since the exhaust gas is "used up", it acts like an inert gas to reduce the amount of fuel and air is introduced into the cylinder.
How would this be interpreted for a system like mine that doesn't have an EGR valve? Or am I missing something else?
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'81 911SC RoW Targa (lot's of goodies)
'07 Lexus IS 250
'84 633 csi (turbo charged-sold)
'68 912 Targa (sold)
"Dream it, Believe it, Decide it, DO it "
Old 04-03-2010, 11:07 PM
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Quote:
Originally Posted by Peter Zimmermann View Post
Here's a little more info; an excerpt from my new book which is now at the publisher...

Once again, emission control requirements take center stage, not only did they send the mighty Turbo packing, a new development for the 911 SC is probably the highlight for 1980. It’s amazing how quickly emission control devices moved from an almost afterthought status to an engineering challenge that played a part in almost every engineering decision. Porsche, often at the forefront of automobile development, installed a three-way catalytic converter fitted with an oxygen sensor on all ’80 SCs. Chemistry was never one of my strong points, but, basically, a three-way catalyst has three jobs:

1. Carbon monoxide (CO) is considered a toxic, non-greenhouse gas. The 3-way cat will cause oxidation of that gas to the less harmful greenhouse gas, carbon dioxide.

2. Hydrocarbons (HC) are unburned, carcinogenic compounds made of carbon and hydrogen. The 3-way cat will cause oxidation of those compounds to carbon dioxide and water.

3. Nitrogen oxides (NOx) are a combination of nitrogen dioxide and nitric oxide, both are poisonous gases. The 3-way cat will cause a reduction of those gases to nitrogen and oxygen.

The three-way catalytic converter replaced the already in-use two-way cat, which would be ineffective in reducing NOx emissions to meet regulatory changes for the 1981 model year. Enter the stoichiometric point, the theoretical point at which combustion is complete. In other words, all the carbon (C) is burned to become CO2, all of the hydrogen (H) is burned to become H2O, etc. The 3-way cat works best when it receives exhaust from an engine that is running slightly lean, above the stoichiometric (ideal) point, which is between 14.8 and 14.9 parts air to 1 part fuel.

When more than the required amount of oxygen exists the engine is running “lean,” which favors the above two oxidizing reactions. When excessive fuel is present the engine is running “rich,” at which point the cat favors the reduction of NOx.

Enter the oxygen sensor. Originally called Lambdasonde by its developer, Bosch, it is a sensor probe that installs into the exhaust just before the catalytic converter. The oxygen sensor measures the remaining oxygen content in the exhaust, and then sends corresponding signals to an electronic control unit (ECU). The ECU is then able to make fine adjustments to fuel delivery, and keep the fuel injection system as near as possible to the ideal stoichiometric point.

Porsche’s use of the 3-way cat and Lambda was so effective that for the first time since 1975 no smog pump (auxiliary air injection) was required. That alone did wonders for the engine compartment’s appearance, as well as improving access to some service related parts such as the ignition distributor. In addition, exhaust gas recirculation (EGR) was also eliminated.
As always, Thank you Peter. Seriously

I'll be sure to pick up a copy once it's available...
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'81 911SC RoW Targa (lot's of goodies)
'07 Lexus IS 250
'84 633 csi (turbo charged-sold)
'68 912 Targa (sold)
"Dream it, Believe it, Decide it, DO it "
Old 04-03-2010, 11:20 PM
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Quote:
Originally Posted by 911Freak View Post
How would this be interpreted for a system like mine that doesn't have an EGR valve? Or am I missing something else?
It means that you should be able to make more power at the expense of higher emissions.

If you look at the history of automakers attempting to meet emission standards, you see they started with primitive systems that robbed power. At first, they leaned out the mixture and used an air pump to provide extra O2 after the combustion chamber to use the exhaust heat to convert CO to CO2 and HC's to CO2 and Water with the unintended result of causing excess heat inthe exhaust systems which caused other mechanical problems. This reduced CO and HC emissions at the expense of higher NOx emissions (due to the hotter cylinder temperatures) and poor engine running (knock and ping issues).

The introduction of the catalytic converter allowed a return to better operating parameters of the engine (i.e. richer running) to produce more power and reduce knocks and pings. The use of fuel injection with the related electronic management allowed automakers to tune the engine for low emissions and good power output.

This is not something to lose much sleep over.
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Last edited by HarryD; 04-04-2010 at 12:35 AM..
Old 04-04-2010, 12:26 AM
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Great info......thanks.

Doyle
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Old 04-04-2010, 02:05 AM
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Quote:
Originally Posted by sjf911 View Post
From the megasquirt manual on emmisions tuning:

This is very helpful as it's a visual reference of most of the data here.

Thanks Steve!
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Old 04-04-2010, 10:40 PM
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Well, I just Googled "Oregon DEQ Standards" and of course ended up at Pelican.

I found this thread interesting, so I thought I'd throw my numbers from this morning (and from 2008) into the mix. The car is my 1980 931 with a mild cam, Bosch CIS, and an Unwired Tools digital control pressure regulator.

HC: 39 PPM, down from 66 PPM (220 allowed)
CO: 0%, down from .0114% (1% allowed)
CO+CO2: 14.3%, up from 13.4% (6% minimum required)

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Old 09-03-2010, 11:03 AM
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