What the table sets
Fuel quantity comes from pulse width. Firing Angle BTDC controls when that pulse happens. The value is in crank degrees before top dead center on the compression stroke, and there's one of these tables for each injection stage, so primary and secondary injectors can be timed separately.
End of Injection vs Start of Injection
What the angle means depends on the Injector Timing Method setting:
| Timing method | The angle in the table is |
|---|---|
| End of Injection (the usual choice) | Where the pulse finishes |
| Start of Injection | Where the pulse begins |
End of Injection is popular for a practical reason. As load and RPM rise, pulse width grows. With the end point fixed, a longer pulse simply starts earlier, and the fuel is still finished at the same point relative to the intake valve. With Start of Injection, a longer pulse stretches later into the cycle instead, which can push fuel delivery past where you intended.
Our approach
Start from a sensible base map value and leave it alone until the fuel table is in good shape. Then make small changes and watch lambda, idle quality and emissions-sensitive areas like light cruise in your logs. Injection timing tends to show its effects most at idle and low load. For the rest of the injector setup, see dead time and injector flow.
