DamonJones
Extreme
OK so something has been bugging me about adjusting CO on our Nytros. Mainly the vast differences in what works for one sled is totally different from what works on another. When I researched CO setting after putting on my exhaust I found that changing CO up (positive numbers) meant you would make the mix richer and down (negative) would make it more lean. After my exhaust I had the standard lean pop when throttling the motor. So I added +4 to all three CO which I eventually tuned down to +3. It seems to run great.
Now here is the problem. Other people have adjusted theirs to numbers like -10, -15 even -20 and say things run great. Again this is usually done after exhaust modification. How can this be?
So I did a bit more research. I found a great site that explains exhaust emissions and what causes different levels of each gas in the exhaust. Here is the link
http://www.autoshop101.com/forms/h56.pdf
Here are some tings I learned. First CO is Carbon Monoxide not to be confused with C02 which is Carbon Dioxide. So the first question that comes to mind is on the ECU what does CO really refer to. You know how engineers like to short descriptions. My guess is that it really is CO however. According to the research high CO levels (usually given as a percentage) comes from a rich air/fuel mix. Further more it is an indication that the motor is not running properly (to much fuel in the mix). So it would make sense that the ECU would give us a way to adjust it if needed. CO2 is actually a good gas. The higher the CO2 the more complete the combustion (CO2 peaks at optimum mixture).
So now comes the confusion, what does the CO adjustment really do? You can look at it two different ways. The first (which is what I did) is to say that if I increase my CO I am adding more fuel per injector pulse (injector stays open longer) which because I have more air flow from my exhaust mod I need more fuel.
BUT and yes there is a but, the CO setting wasn’t built into the ECU to help us guys out that are modifying their sleds. It was put there as a way to adjust emissions on the factory sled. So you could say that if the a gas analyzer is reading a high CO (mix to rich) that you tell the ECU that the reading was too high and by putting in positive values the ECU would then make a correction to the mix based on your observation in effect leaning the mix. In my case this makes no sense but explains what other have experienced.
Another issue, If you look at the graph in the link you will notice that CO changes very little on the lean side of the optimum air fuel mix but changes drastically on the rich side. Oxygen on the other hand is just the opposite. This explains why reading O2 for the turbo guys is so much better. A lean motor especially boosted is going to cannonball. Why is this important? It means that CO is a great measure of a rich engine but a poor measure of a lean one. It also supports the theory that adjusting CO based on the reading from an analyzer is how the CO setting works. Here is why. If we assume that the ECU CO setting of 0 is the base line for a normal stock motor at perfect fuel mixture. If my exhaust analyzer tells me that my CO was say .5% if you look at the graph that’s a lean mix of 21. Way off so a large negative number should be put into the ECU. The ECU would then take that information and correct the mix by making it richer. This totally explains the large negative numbers that some people have reported to make their Nytros run after putting on exhaust.
So some testing is in order. I’m going to see if I can get my hands on a gas analyzer and play with the CO settings. Anyone else have any thoughts?
Now here is the problem. Other people have adjusted theirs to numbers like -10, -15 even -20 and say things run great. Again this is usually done after exhaust modification. How can this be?
So I did a bit more research. I found a great site that explains exhaust emissions and what causes different levels of each gas in the exhaust. Here is the link
http://www.autoshop101.com/forms/h56.pdf
Here are some tings I learned. First CO is Carbon Monoxide not to be confused with C02 which is Carbon Dioxide. So the first question that comes to mind is on the ECU what does CO really refer to. You know how engineers like to short descriptions. My guess is that it really is CO however. According to the research high CO levels (usually given as a percentage) comes from a rich air/fuel mix. Further more it is an indication that the motor is not running properly (to much fuel in the mix). So it would make sense that the ECU would give us a way to adjust it if needed. CO2 is actually a good gas. The higher the CO2 the more complete the combustion (CO2 peaks at optimum mixture).
So now comes the confusion, what does the CO adjustment really do? You can look at it two different ways. The first (which is what I did) is to say that if I increase my CO I am adding more fuel per injector pulse (injector stays open longer) which because I have more air flow from my exhaust mod I need more fuel.
BUT and yes there is a but, the CO setting wasn’t built into the ECU to help us guys out that are modifying their sleds. It was put there as a way to adjust emissions on the factory sled. So you could say that if the a gas analyzer is reading a high CO (mix to rich) that you tell the ECU that the reading was too high and by putting in positive values the ECU would then make a correction to the mix based on your observation in effect leaning the mix. In my case this makes no sense but explains what other have experienced.
Another issue, If you look at the graph in the link you will notice that CO changes very little on the lean side of the optimum air fuel mix but changes drastically on the rich side. Oxygen on the other hand is just the opposite. This explains why reading O2 for the turbo guys is so much better. A lean motor especially boosted is going to cannonball. Why is this important? It means that CO is a great measure of a rich engine but a poor measure of a lean one. It also supports the theory that adjusting CO based on the reading from an analyzer is how the CO setting works. Here is why. If we assume that the ECU CO setting of 0 is the base line for a normal stock motor at perfect fuel mixture. If my exhaust analyzer tells me that my CO was say .5% if you look at the graph that’s a lean mix of 21. Way off so a large negative number should be put into the ECU. The ECU would then take that information and correct the mix by making it richer. This totally explains the large negative numbers that some people have reported to make their Nytros run after putting on exhaust.
So some testing is in order. I’m going to see if I can get my hands on a gas analyzer and play with the CO settings. Anyone else have any thoughts?
DamonJones
Extreme
Another interesting comment posted on another forum. The suggestion was made that even though the adjustment range of the CO setting is say +128 to -128 (I forget what it actuially is) that the adjustment will not let you adjust CO way out of spec or to a value that is not practical (meaning the engine won't run at). When looking at the graph CO line it would make sense that large negative numbers make smaller adjustments relative to posative numbers. This would explain the large negative numbers I have seen and the small posative ones.
SledNeck91604
Extreme
so does this mean that when you are adjusting the CO up and down with the help of a gas analyzer, you are basically just relaying the rich or lean mixture that the gas analyzer reads to the sleds ECU?
basically saying to the ecu, "hey, your to lean, fix it"
basically saying to the ecu, "hey, your to lean, fix it"
YamaMTX
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Awesome info thanks for that!
DamonJones
Extreme
SledNeck91604 said:
That's the million dollar question.
Another thought, that I guess needs to be proved as well is do some aftermarket exhaust actually restrict flow. This would mean we would need to lean the mix, hence nagative adjustment and a large one because of the reasons I mentioned about the CO line curve.
To make things even move complex do they actaully restrict more than the stock setup and some RPMs and flow better than stock at others. That could explain why some setups require fuel controller like the PCIII and others don't. Gets really complx real quick when you think about it. The stock ECU map was designed around the stock exhaust. Who is to say that an after market setup will linearaly follow the stock setup. My guess is about 0% chance of that.
