BRZ: Calibrating larger injectors

After installing a set of larger port injectors it is very important to ensure that the ECU knows their true size so that it can accurately calculate the correct injector opening time for a given volume of fuel.

After fitting larger port injectors the following maps will need re-scaling…

• Port Injector Scaling
• Injector Opening Time Compensation
• Injector Minimum Open Time

The larger port injectors should be supplied with an injector calibration size, and this should be entered here…

The different injectors will have different characteristics from the standard injectors and will normally take longer to open. This time period is referred to as ‘dead time, lag time or latency’ and is affected by the current battery voltage.

Using the manufacturer's technical data, enter the correct lag times for a given voltage in the maps called Injector Opening Time Compensation.

If this data is not available we suggest you just change the injector size then leave the battery voltage compensation map until you see how the engine is running.

You should now follow the sequence given under How to Set Up an Intake or Induction Kit and pay attention to the fuel trims in closed loop. Also watch the wide-band AFR sensor in open loop to see how far out the AFR is compared to the fuel map targets.

The fuel map should be filled with a fixed value (such as 12:1 AFR) for simplicity of adjusting the calibration and cross-referencing with the wide band.

The Injector Opening Time Compensation values will have much more of an effect at idle and light load when the injector open times are much smaller (2-5ms at idle and light load vs 10-18ms for full load).

In addition, where larger port injectors are fitted it may be advantageous to fine tune the DI/PI ratio to ensure that the DI injectors are delivering enough fuel volume and that the bigger PI injectors don't deliver it all; they should supplement the DI, not replace it.

Remember that the port injectors can open up to 18ms at 6000rpm, whereas the DI can only inject for less than half of that (due to spark BTDC and valve overlap), so around 5ms MAX is recommended for DI.

Changes should also be made to the PI/DI ratio map along with the Min and Max allowed ratios for larger injectors.