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fueltrimupdatepoints [2009/07/13 10:47]
2gDSM
fueltrimupdatepoints [2024/03/15 11:16] (current)
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 In **closed loop** mode, the ECU checks itself by "​watching"​ the front O2 sensor feedback. ​ The factory front O2 sensor switches abruptly around 14.7:1 A/F ratio (assuming gasoline). ​ The ECU tries to adjust fuel so that the O2 sensor swings back and forth around this target. ​ To do that, the ECU has to have some way to vary its basic fuel calculation. ​ It uses fuel trims for this purpose. ​ Think of these variables as dials if you want.  Turn the dial one way and the ECU adds fuel, turn the dial the other way and the ECU reduces fuel. In **closed loop** mode, the ECU checks itself by "​watching"​ the front O2 sensor feedback. ​ The factory front O2 sensor switches abruptly around 14.7:1 A/F ratio (assuming gasoline). ​ The ECU tries to adjust fuel so that the O2 sensor swings back and forth around this target. ​ To do that, the ECU has to have some way to vary its basic fuel calculation. ​ It uses fuel trims for this purpose. ​ Think of these variables as dials if you want.  Turn the dial one way and the ECU adds fuel, turn the dial the other way and the ECU reduces fuel.
  
-While running **closed loop** mode, the ECU uses what's called a "short term fuel trim" (STFT) variable for quick changes. ​ This is the variable it uses to force the O2 sensor to cycle. ​ In a perfect setup, this variable would swing from positive to negative values of about equal amplitude. ​ As it's swinging up and down, the front O2 sensor should swing up and down.  This is the basic **closed loop** mode of operation.+While running **closed loop** mode, the ECU uses what's called a "short term fuel trim" (STFT) variable for quick changes. ​ This is the variable it uses to force the O2 sensor to cycle. ​ In a perfect setup, this variable would swing from positive to negative values of about equal amplitude. ​ As it's swinging up and down, the front O2 sensor ​signal ​should swing up and down.  This is the basic **closed loop** mode of operation.
  
 The ECU will also watch what's going on with the short term fuel trim variable. ​ If conditions are right and the short term variable has stayed positive or negative long enough, the ECU will move the long term STFT pattern into the long term variable (LTFT). ​ This is called a **learning mode**. ​ Let's say instead of swinging around 0%, STFT is swinging up and down around -5%.  The ECU will eventually take note of this and move that -5% adjustment into the appropriate LTFT variable and then zero out the STFT variable. ​ Since both are factored in, the end result will be the same but STFT should now swing around 0%. The ECU will also watch what's going on with the short term fuel trim variable. ​ If conditions are right and the short term variable has stayed positive or negative long enough, the ECU will move the long term STFT pattern into the long term variable (LTFT). ​ This is called a **learning mode**. ​ Let's say instead of swinging around 0%, STFT is swinging up and down around -5%.  The ECU will eventually take note of this and move that -5% adjustment into the appropriate LTFT variable and then zero out the STFT variable. ​ Since both are factored in, the end result will be the same but STFT should now swing around 0%.
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   * Baro >= 22.9 inHg   * Baro >= 22.9 inHg
   * Baro <= 31.6 inHg   * Baro <= 31.6 inHg
 +
  
 ====== LTFT Select ====== ====== LTFT Select ======
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 That will give you three long term fuel trim values, just like the 1G guys. That will give you three long term fuel trim values, just like the 1G guys.
  
-Thomas Dorris 
fueltrimupdatepoints.1247496434.txt.gz ยท Last modified: 2009/07/13 10:47 by 2gDSM