2JZ-GE Cam & Crank Signals

The IS300 Overall Wiring diagrams show a camshaft and crankshaft position sensor connected to the ECU.  These sensors are variable_reluctance sensors and provide the ECU with engine position information, which is used for fuel and ignition control.

In preparation for building the electrical circuit and writing the firmware for 2JZduino, an investigation was necessary to identify the nature of these cam and crank sensor signals.  This would have been easiest with an Oscilloscope, but unfortunately I do not have easy access to one of these.  Instead, I built a data acquisition unit using the analog input channels of the Arduino Mega.  I tapped into the cam and crank signals at the ECU, connecting them to analog input channels 6 and 7.  A diode was connected between analog input signal (cathode) and ground (anode) to protect the Arduino against negative voltages generated by the sensors.

An excerpt of the code written to sample analog channels 6 & 7 is posted below.  Data acquisition rate for both channels is ~5,000 Hz, which is limited primarily by the serial port (limiting the speed at which data is extracted from Arduino).  The myDataLogger object (code not shown) has both “Store” and “Transmit” methods.  “Store” places the analog input values into a private member myDataLogger.buffer from within the interrupt service routine.  “Transmit” is called during the main loop of program execution which transmits the data sequentially over serial port to a listening software program which then re-assembles the data for graphing.

void setup()
{
  // setup ADC
  ADMUX = B01100110;  // AVCC VRef, ADC Left, ch6
  ADCSRB = B00000000; // Analog Input bank 1
  ADCSRA = B11001111; // ADC enable, ADC start
    // manual, interrupt enable, prescaler = 128
}

ISR(ADC_vect) { // Analog->Digital Conversion Complete
  static byte Channel6 = 0;
  static byte Channel7 = 0;

  char ADCch = ADMUX & B00000111;  // which channel?

  if (ADCch == 6) {
    Channel6 = ADCH;  // store ADC result
    ADMUX = (ADMUX & B11100000) + 7;  // set channel 7
  }
  else if (ADCch == 7) {
    Channel7 = ADCH;  // store ADC result
    ADMUX = (ADMUX & B11100000) + 6;  // set channel 6
    myDataLogger.Store(Channel6, Channel7);
  }

  ADCSRA |= B11000000;  // start next ADC
}

The charts below show the captured cam and crank signals for my 2JZ-GE during engine cranking and during idle.  Note that these are the positive side of the waveform only because the Arduino analog inputs measure only positive voltages.

The engine idle is about 1300 RPM (this slows to ~700 RPM after the engine is warm).  Analysis reveals that the crank signal arrives for every 10 degrees of engine rotation and is generated 34 times in 360 degrees (there is no crank signal for 20 degrees of the revolution).  The cam signal arrives every 240 degrees of rotation so that there are 3 signals for each 720 degrees of rotation (each complete Otto cycle).  It seems that the stock ECU would identify the beginning of the engine cycle when the falling-edge of the cam signal and the 20 degree gap in the crank signal align.

Also worth noting is the magnitude of the peak signal voltage between startup (< 2 V) and idle (> 4 V).  The low peak-voltage at slow engine speeds will prevent signal detection to be done directly by the Arduino digital inputs.  This will be discussed in more detail when the circuit and acquisition logic design is discussed.