engineandecu101
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| ==== Closed loop ==== | ==== Closed loop ==== | ||
| Closed loop mode is explained in more detail on the [[fueltrimupdatepoints|Fuel Trims]] page. Please read this page and really understand how fuel trims play a role in closed loop mode of operation. They are very important numbers when it comes time to dial in a new set of injectors, for example. | Closed loop mode is explained in more detail on the [[fueltrimupdatepoints|Fuel Trims]] page. Please read this page and really understand how fuel trims play a role in closed loop mode of operation. They are very important numbers when it comes time to dial in a new set of injectors, for example. | ||
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| ==== Open loop ==== | ==== Open loop ==== | ||
| + | When the ECU is running in open loop mode, it still starts with a 14.7:1 estimation of air/fuel ratio, just as it does in closed loop mode. But then it applies an enrichment factor based on a table look up. This factor will almost always add more fuel to the mixture. So instead of a 14.7:1 air/fuel ratio (A/F), the ECU may try to run 9.5:1. As you increase fuel, you increase the denominator in the air/fuel ratio and as a result you decrease the ratio value. This ratio is said to become "richer" as you add fuel. It becomes "leaner" as you take fuel away. | ||
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| + | The "closed loop" target of 14.7:1 is called the stoichiometric ratio for gasoline. This ratio is the theoretically "ideal" mixture where all fuel is combined with all the free oxygen exactly. This is the ratio the ECU targets under light load conditions (idle/cruise). But it is inappropriate as load increases. As engine load increases, it generally becomes less tolerant of "lean" mixtures. Trying to run an engine too lean for the operating conditions can cause things to melt or can cause the combustion process to break down and "explode" rather than burn (typically called detonation or knock). So it's important to keep the mixture rich enough to prevent this but lean enough to make decent power. | ||
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| + | So when running "open loop", the ECU does not always target 14.7:1. It targets an A/F ratio that depends on load and RPM. The picture below illustrates what this type of target table looks like. You can see that as RPM and load increase, the target A/F ratio gets richer and richer. | ||
| {{ http://www.ecmtuning.com/images/forums/ecmlink101/2gdsmafr3d.gif }} | {{ http://www.ecmtuning.com/images/forums/ecmlink101/2gdsmafr3d.gif }} | ||
engineandecu101.txt ยท Last modified: 2024/03/15 11:16 (external edit)
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