Running too rich or too lean, how its effected
02-14-2006, 09:30 PM
#21
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Originally Posted by s2kBryan916,Feb 14 2006, 10:26 PM
Just to add, I am saying that the computer is trying to do this during Closed Loop operation not when it is in Open Loop. Open Loop occurs during WOT, Decel, Startup etc.
02-14-2006, 09:31 PM
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I will see tomorrow what the stock S2000 runs at. At my school we have a S2000 that is going to be raced at Thunderhill Raceway park soon. The motor is bone stock. I will for sure post my findings and hopefully you can use that to judge how far you are tuning it rich to lean. Having a base point might help to judge to lean or to rich.
02-14-2006, 09:36 PM
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This may help. It is directly from a training program I have.
Fuel System Status
Fuel system status is indicated as ''open'' or ''closed''.
Closed: Based on the HO2S output, the ECM determines the air/fuel ratio and controls the amount of injected fuel.
Open: Ignoring HO2S output, the ECM refers to signals from the throttle position (TP), manifold absolute pressure (MAP), intake air temperature (IAT), barometric pressure (BARO) and engine coolant temperature (ECT) sensors to control the amount of injected fuel.
At idle speed: closed
YES
Short Term Fuel Trim
The air fuel ratio correction coefficient for correcting the amount of injected fuel when the Fuel System Status is ''closed''. When the ratio is leaner than the stoichiometric ratio, the ECM increase short term fuel trim gradually, and the amount of injected fuel increases. The air fuel ratio gradually gets richer, causing a lower oxygen content in the exhaust gas. Consequently, the short term fuel trim is lowered, and the ECM reduces the amount of injected fuel. This cycle keeps the air/fuel ratio close to the stoichiometric ratio when in closed loop status.
If you dont understand that I dont know how else to explain it. This is Directly from Honda about the S2000
Fuel System Status
Fuel system status is indicated as ''open'' or ''closed''.
Closed: Based on the HO2S output, the ECM determines the air/fuel ratio and controls the amount of injected fuel.
Open: Ignoring HO2S output, the ECM refers to signals from the throttle position (TP), manifold absolute pressure (MAP), intake air temperature (IAT), barometric pressure (BARO) and engine coolant temperature (ECT) sensors to control the amount of injected fuel.
At idle speed: closed
YES
Short Term Fuel Trim
The air fuel ratio correction coefficient for correcting the amount of injected fuel when the Fuel System Status is ''closed''. When the ratio is leaner than the stoichiometric ratio, the ECM increase short term fuel trim gradually, and the amount of injected fuel increases. The air fuel ratio gradually gets richer, causing a lower oxygen content in the exhaust gas. Consequently, the short term fuel trim is lowered, and the ECM reduces the amount of injected fuel. This cycle keeps the air/fuel ratio close to the stoichiometric ratio when in closed loop status.
If you dont understand that I dont know how else to explain it. This is Directly from Honda about the S2000
02-15-2006, 07:14 AM
#24
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Originally Posted by s2kBryan916,Feb 15 2006, 12:21 AM
I know for sure a HUGE majority of cars in the US today do run around a 14:7.1 ratio OR are trying to be at the ratio. It will lean it out when it needs to, like many ULEV (ultra low emissions vehicles) in fact the Honda Accord will lean it to a 22:1 ratio WAY lean, but it is able to do so because it has an air fuel sensor rather than a O2 sensor.
[QUOTE]I am not saying that the s2000 doesnt run at a richer mixture than what is normally done by most cars now adays.
02-15-2006, 07:24 AM
#25
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also, kayvan, one thing you should realize. VAFC will get you gains as you dyno tune. over time, however, you will lose some of those gains, as the ECU will tend to richen the fuel mixture again as it "learns" the VAFC. this is the problem with the piggy back method of tuning on the S2000. not to say that it makes it useless, but just realize some of the gains will be negated over time. 
02-15-2006, 08:48 AM
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Originally Posted by Wisconsin S2k,Feb 15 2006, 08:14 AM
also, your talk about the air/fuel ratio in scenarios where it is not WOT is just confusing the matter, since we're talking about dyno tuning and WOT, so let's stick to WOT only please.
02-15-2006, 09:42 AM
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Originally Posted by Wisconsin S2k,Feb 15 2006, 08:24 AM
also, kayvan, one thing you should realize. VAFC will get you gains as you dyno tune. over time, however, you will lose some of those gains, as the ECU will tend to richen the fuel mixture again as it "learns" the VAFC. this is the problem with the piggy back method of tuning on the S2000. not to say that it makes it useless, but just realize some of the gains will be negated over time.
But, if I just reset the ecu I shouldn't have to worry about this problem happening correct?
02-15-2006, 09:44 AM
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Originally Posted by Twiztid,Feb 15 2006, 09:10 AM
Thank you , Thank you , Thank you
This is the smartest thing I have read this morning .
------------------------------
Kayvan I know we got into this debate before . But you demanded you are a pro tuner . You would not be asking these questions if you understood how the factory computer works .
Your car is always changing its short term and long term fuel trim maps . At cruising speed your car is trying to keep everything at 14.7 A/F when in closed loop . Thus always rewriting ( Short term fuel changes about 4 times a sec. ) thus overall effecting long term trim . When your car goes into open loop it looks back at the long term fuel to determine what to run at .
Also setting your VAFC for 80% TP does not make a difference as the ecu doesn't use just TP to determine if it is in open or closed loop mode . It uses and reads manifold pressure to determine how much load is being put on the engine . We can get our boosted car to go into open loop at as little as 15% TP .
When the VAFC and SAFC were first introduced it was on OBD1 cars which did not rely of O2 feedback as much .
You would have better results manipulating the water temp sensor than the MAP .
So to answer your question , you will not have to touch the VAFC as the factory computer has already relearned your setting and will adjust for the new mods . The best thing you can do is invest in a scan tool so you can read your long term and short term to make sure you are not maxing it out .
And resetting the ecu will not fix this problem as you will be on different set of tables than when you tuned the car on the dyno . And even if you reset the Ecu before you dynoed it was changing the shorterm and longterm trims on every pull , so you would see improvements without touching the VAFC for the first pull till around the 3rd or 4th pull .
This is the smartest thing I have read this morning .
------------------------------
Kayvan I know we got into this debate before . But you demanded you are a pro tuner . You would not be asking these questions if you understood how the factory computer works .
Your car is always changing its short term and long term fuel trim maps . At cruising speed your car is trying to keep everything at 14.7 A/F when in closed loop . Thus always rewriting ( Short term fuel changes about 4 times a sec. ) thus overall effecting long term trim . When your car goes into open loop it looks back at the long term fuel to determine what to run at .
Also setting your VAFC for 80% TP does not make a difference as the ecu doesn't use just TP to determine if it is in open or closed loop mode . It uses and reads manifold pressure to determine how much load is being put on the engine . We can get our boosted car to go into open loop at as little as 15% TP .
When the VAFC and SAFC were first introduced it was on OBD1 cars which did not rely of O2 feedback as much .
You would have better results manipulating the water temp sensor than the MAP .
So to answer your question , you will not have to touch the VAFC as the factory computer has already relearned your setting and will adjust for the new mods . The best thing you can do is invest in a scan tool so you can read your long term and short term to make sure you are not maxing it out .
And resetting the ecu will not fix this problem as you will be on different set of tables than when you tuned the car on the dyno . And even if you reset the Ecu before you dynoed it was changing the shorterm and longterm trims on every pull , so you would see improvements without touching the VAFC for the first pull till around the 3rd or 4th pull .
so the only way around this would to buy an AEM EMS correct???
02-15-2006, 09:52 AM
#30
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Originally Posted by kayvan_pour,Feb 15 2006, 01:42 PM
But, if I just reset the ecu I shouldn't have to worry about this problem happening correct?