GT-R: Enhanced Injector Control

6/6/2017

Nissan uses a very basic system for Injector control in the R35 ECU which leaves a lot to be desired, especially when replacing the factory injectors with a higher flowing aftermarket set. With most GTR's running injectors with a much larger flow capacity, we decided it was time to write some custom code in order to handle fueling in a much more robust, flexible, and elegant way. The following table and feature additions should help in tuning cars with larger than stock injectors where low pulsewidth linearity, fuel temperature, fuel pressure, and latency issues can become a problem. 

3D Injector Latency

The first new table we offer is a 3D Injector Latency Table.  This table allows users to specify injector latency across battery voltage and differential fuel pressure as opposed to the OEM linear multiplier and offset method. Values in this table will override OEM calculated latency. The 3D latency table will need to be enabled in order to use this new strategy by setting the 3D Injector Latency - Enable table to a value of 1. Base fuel pressure will also need to be input into the Base Fuel Pressure table. Base fuel pressure is determined by your fuel pressure regulator when referenced to atmospheric pressure. 

3d Injector Latency - Enable This table will need to be set to 1 (Enabled) in order to use the new 3D latency table in place of the OEM linear multiplier and offset method. Plug and play data for COBB/ID injectors is provided here.

Non-Linear Injector Compensation

Accesstuner now offers a new Non-Linear Injector Compensation table that applies a fuel injector compensation to correct for non-linear operation of the fuel injector at very low pulsewidths. The Y-Axis of this table is differential fuel pressure. If fuel pressure input is disable in the safety tables section, the input to this axis will be your base fuel pressure table value. This table is available to be edited in realtime. The values in the realtime table will persist until a map switch, battery disconnect, or ECU flash is performed. You must manually copy any changes in this table into the non-realtime non-linear injector compensation table to be flashed with the calibration. This table also requires a value of 1 (Enabled) to be entered into the Non-linear Injector Compensation - Enable table for the feature to be active. Plug and Play data for COBB/ID injectors is provided here. An upper limit threshold has also been added to this feature. The Non-Linear Injector Compensation Maximum IPW table is used to set the upper threshold for non-linear injector compensation. When pre-compensation effective pulsewidth is above this value, compensation will no longer be applied.

This table will need to be set to 1 (Enabled) in order to use the new Non-Linear Injector Compensation feature. 

This table will set the maximum injector pulsewidth where Non-linear compensation will be used. 

Differential Fuel Pressure Compensation

In order to both optimize performance and add additional safety measures to your tune, Accesstuner now has a new Differential fuel pressure compensation system.  The new system applies a global fuel injector compensation based on the differential fuel pressure error percent. Differential fuel pressure is calculated as (fuel pressure - manifold relative pressure). Differential fuel pressure error percent is calculated as ((differential fuel pressure/base fuel pressure)-1)*100. There are a few parameters outlined below that need to be set in order to make this system work correctly. 

The Base Fuel Pressure table should match the base fuel pressure as set by your fuel pressure regulator when referenced to atmospheric pressure. This value will be used to calculate differential fuel pressure when a fuel pressure sensor is installed and enabled in the fuel pressure safety section. Differential fuel pressure will be set to this value when a fuel pressure sensor is not installed and enabled. The 3D latency Y-axis will always reference differential fuel pressure whether a fuel pressure sensor is installed or not. This table should always be set to the vehicles base fuel pressure in order for the 3D latency to function correctly. 

The Differential Fuel Pressure Compensation table is the main table in the system that will apply a global fuel injector compensation based on differential fuel pressure error percent.Differential fuel pressure is calculated as (fuel pressure - manifold relative pressure). Differential fuel pressure error percent is calculated as ((differential fuel pressure/base fuel pressure)-1)*100.

The Differential Fuel Pressure Compensation - Enable table will need to be set to 1 (Enabled) in order to use the new differential fuel pressure compensation feature. 

Differential Fuel Pressure Compensation Minimum Boost table is the minimum relative pressure threshold required to enable differential fuel pressure compensation. 

Differential Fuel Pressure Compensation Minimum Boost Hysteresis is a hysteresis (or slight delay) applied to differential fuel pressure compensation minimum boost threshold. Manifold relative pressure must drop below the Differential Fuel Pressure Compensation Minimum Boost threshold by this table value before differential fuel pressure compensation will be deactivated. 

Differential Fuel Pressure Compensation Minimum RPM is the minimum Engine Speed threshold required to enable differential fuel pressure compensation. 

Differential Fuel Pressure Compensation Minimum RPM Hysteresis is a value applied to differential fuel pressure compensation minimum RPM threshold. Engine speed must drop below the Differential Fuel Pressure Compensation Minimum RPM by this table value before differential fuel pressure compensation will be deactivated. 

Differential Fuel Pressure Smoothing (Frequency Cut-Off)This table specifies a maximum allowable oscillation frequency for the differential fuel pressure value. Lower values in this table will induce more smoothing. This table will act as a software low pass filter to differential fuel pressure. 

Fuel Temperature Compensation

Accesstuner now has fuel temperature compensation. Fuel temperature compensation applies a global fuel injector compensation based on fuel temperature to correct for fuel density changes. Gasoline and ethanol changes in density at around a 0.10-0.11% per degree Celsius rate.

Fuel Temperature Compensation, This table is the main table in the system that will apply a global fuel injector compensation based on fuel temperature. 

Fuel Temperature Compensation - Enable This table will need to be set to 1 (Enabled) in order to use the new fuel temperature compensation feature.

Minimum Injector Pulsewidth (COBB)

Accesstuner now has a minimum injector pulsewidth table that represents a final minimum pulsewidth for all fuel injector pulsewidth calculations. The OEM minimum pulsewidth is applied before Alpha and other compensations and does not work well to limit effective pulsewidth as compensations can pull actual effective pulsewidth below the OEM value. It is recommend to set the OEM minimum pulsewidth to zero and use this table as an actual minimum pulsewidth value.