fueltrimupdatepoints
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fueltrimupdatepoints [2008/06/26 13:31] twdorris |
fueltrimupdatepoints [2008/09/06 05:11] twdorris |
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| In a nut shell, while running **open loop** the ECU just assumes it knows how much fuel is really going in and it assumes that accurate airflow data is being presented to it. It does not check these assumptions against anything. It just calculates how much fuel is needed to achieve a certain A/F ratio based on airflow data. It looks this target A/F ratio up in an **open loop** fuel table indexed by RPM and engine load. | In a nut shell, while running **open loop** the ECU just assumes it knows how much fuel is really going in and it assumes that accurate airflow data is being presented to it. It does not check these assumptions against anything. It just calculates how much fuel is needed to achieve a certain A/F ratio based on airflow data. It looks this target A/F ratio up in an **open loop** fuel table indexed by RPM and engine load. | ||
| - | 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. 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 should swing up and down. This is the basic **closed loop** mode of operation. | ||
fueltrimupdatepoints.txt ยท Last modified: 2024/03/15 11:16 (external edit)
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