GTR OEM Transient Fueling

The GTR ECM continuously calculates the volume of fuel that the injectors deposit on the intake port wall and it uses this calculated value to make corrections for the fuel injector pulse width directly during transient airflow and engine load conditions. The GTR uses two types of transient correction a global and an individual cylinder correction and they appear to be independent of each other and added at different points of the fuel injector open time calculation function.

Globally Applied Transient Corrections

The global calculation initially finds the change in wall wetting volume and air quantity to set an addition of injector pulse width (ms) to the normal injector open time. It does this using the Fuel Wetting Volume maps, target AFR and number of cylinders to find a fuel volume on the wall at the current engine position and for the previous measured state and multiplies it by the air quantity calculated. This can be positive and negative depending on acceleration or deceleration and there are many other compensations that are applied depending on whether the driver is accelerating or decelerating. There are many maps involved and in general tuning the SDVE or MAF maps will inevitably compensate for the static amount of fuel on the port wall, however, if you knew the wall wetting volume created by your injectors or wanted to test the results of changing what the ECU thinks is deposited on the port wall the key maps to make adjustments are the Fuel Wetting volume and Air quantity rate maps are basis maps shown below.  These have not been added to all ROMs as we have not found the need to change them.

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Individual Cylinder Corrections for transient throttle

The first task of the individual cylinder fuel compensation function is to calculate the change in fuel volume required by the change in load for each individual cylinder.  This value is then used in a series of calculations and corrections with maps to give a final individual cylinder transient compensation injector open time.  There is a threshold of change in load that when exceeded uses a similar set of calculations but stats to apply them by interrupting the current injector open time and extending and reducing that value while the injector is open.

Functions use a series of 2D maps which it selects depending on if the change in load is positive or negative. It has a set of maps hat effect the compensation whether accelerating or decelerating and then individually tune-able maps for both accel and decel. The two different methods of individual cylinder pulse width adjustment work in very similar methods but use different correction maps and factors.  When tuning the transient fueling of a GTR the following maps have the most effect, they are not a direct millisecond output but directly influence the injector time, to tune them you will have to review the effects of changes in logs and further increase or decrease the values depending on the results seen.  They are multipliers of the calculated pulse width extension value and are used to adjust the calculated amount for different injectors sizes and spray patterns for transient fuel condition (changing amounts of fuel on the port wall).

The transient Comp temperature factor is a compensation that effects both accel and decal compensation maps as a multiplier, broad adjustment to transient fueling during tip in and tip out of the accelerator can be made with this map.

Transient Comp B Base and RPM maps affect the transient fueling during acceleration based on engine coolant temperature and engine speed. You would use these maps to increase or decrease the amount of fuel when tipping in or increasing the accel pedal value.

We believe the Transient comp related map is used in the interrupted injection amount function but modifies a factor from the normal value to ensure that the transition is smooth.

Transient Comp C Decel Base and RPM factors effect the deceleration enrichment based on engine coolant temperature and engine speed, you should use these maps to decrease or increase the mount of fuel injected when tipping out or decreasing the accelerator pedal value.

You can see the effects of the decel compensation map testing below

We believe that transient comp C Load factor is used in the decel calculation and is based on the current engine load.

It is believed that Transient comp C accel Base and RPM factors are below the threshold for the current injection time interrupt function so generally do not have much of an effect on the transient conditions we need to tune for.