A fuel map is the combination of everything an ECU knows about engine running conditions. The goal of a fuel map is to use this information to provide the right amount of fuel. It does this by controlling fuel injector pulse width. Pulse width (PW) is the amount of time an injector is open in milliseconds.
In this fuel map example the base map is in the lower section. It is comparing engine RPM,
The upper section lists sensor information and how it affects pulse width (Mod/Compensation). This is shown as a percentage. It also lists the target and actual Air/Fuel Ratio (AFR).
In this example the computer is operating in open loop. In open loop, feedback from the
- The engine is below operating temperature.
- Target AFR is higher than actual AFR.
- No Closed Loop Compensation is happening.
Once the engine warms up, the oxygen sensor will be used to modify pulse width. This is called closed loop. Closed Loop Compensation is also known as fuel trim. Fuel trim can either add or subtract fuel from the map depending on whether the O2 sensor reads lean or rich.
How does this affect performance?
The fuel map controls engine performance. Map values can be adjusted to improve power, efficiency, and drivability across the entire rpm range. Controlling your fuel map is the key to optimizing an engine for its intended use.