Injector Breakpoint

The pulse width where injector flow transitions from the low-slope region to the high-slope region.

The breakpoint is the pulse width (or fuel mass) at which the ECU switches from using the low-slope characterization to the high-slope characterization of the injector. Injectors flow nonlinearly at short pulse widths near their minimum opening, so the calibration models two regions and the breakpoint is where they meet. It matters because errors here show up as fueling drift at light load and tip-in, where the injector spends time in the low-flow region, even when WOT fueling looks perfect. Setting the breakpoint and low slope correctly is what makes big injectors idle and cruise cleanly instead of stumbling or fouling. In HP Tuners VCM Editor it appears in the Fuel Injector data set with the high and low slopes and the offset. Use the injector manufacturer's published data when available, then fine-tune by logging low-load AFR and trims with a wideband.