Theory of Nissan / JECS operation

The ECU's task is to control the operation of the engine. From starting, idleing to actually producing large amoun tof power, the ECU controls it all. These ECU's operate around two primary sensors, the CAS (Cam Angle Sensor) and the AFM (Air Flow Metre). With these two primary sensors the ECY is able to determine load and crank angle. Then, it determines how much fuel to insert, and when to fire the coil(s). Our main concern is how constants are changed to accomodate different modification and get the best, and fastest, results from the car.

The Constants

The main constant useful to ECU modification is referred to as the 'K's' constant. Altering this constant changes the main multiplier for how much fuel is injected.

• The higher the number, the more fuel that is injected
• The bigger the injector, the smaller the constant
• The bigger the AFM, the larger the constant

The next most important factor is the "invalid injector time' also known as injector dead time. This is the time adjuster that is added to the injector time to compensate for the opening or closing delay from the pulse to physical actuation of the fuel injector. This is added onto the pulse width at the very end of the calculation.

Other constants include RPM and speed.

The Maps

There are three main components for every map. Two scales are used, RPM/Base calculated injection time and map value.
In injection maps, the map valyes are in degrees (BTDC). In fuel maps, the values are a correction factor from the base calculated injection time, commonly referred to as the TP scale.

• Value of 0-127 is (TP * (1 + (Value / 128))) *0.125 = injection time (ms)
• Value of 128-255 is (TP * ((Value – 64) / 1288)) * 0.125 = injection time (ms)

Futher to this, values from 128-255 are considered under O2 sensor control, meaning map values are only base figures. Correction factor from the O2 feedback should be calcuated on top of this figure.