The basic working principle of the Toyota computer control ignition circuit is that the electronic control unit (ECU), according to the engine load provided by the throttle position sensor (or air flow sensor or intake manifold pressure sensor), the engine speed sensor and the cooling water temperature sensor, Speed ​​and cooling water temperature and other signals to determine the best ignition advance angle, and crankshaft angle sensor based on the crank angle signal output ignition timing (IGT) signal, and the ignition is to determine and control the primary circuit power time. When the ECU outputs the IGT signal and the ignition coil primary current is interrupted to achieve ignition, the igniter outputs an ignition confirmation (IGF) signal to the ECU. If the ECU does not receive the IGF signal, the ECU immediately stops the fuel injection of the injector. If the ECU detects that the IGT or IGF circuit is open or shorted, that is, the ECU does not receive the IGF signal after continuously outputting the IGT signal four times, the ECU considers the ignition to be faulty. According to the basic working principle, you can use the ignition signal (IGF and IGT signal) on the computer control ignition circuit failure analysis.
    1, IGF signal detection and analysis
    When the engine is started, use the multimeter to measure the IGF pin voltage on the ECU harness side connector, ie the IGF signal voltage, which should be 0.8V-1.2V. If the IGF signal voltage does not meet the standard, remove the igniter harness side connector After the ignition switch is placed in the ignition (ON) position (the engine is not running), and then measure the IGF terminal voltage. At this time, if the IGF terminal voltage is 4V-5V (ECU-supplied voltage), it indicates that the igniter, ignition coil or its line is faulty; otherwise, the ECU, distributor or its line is faulty, or there is no power supply voltage on the ECU.
    2, IGT signal detection and analysis
    A. Start the engine with a multimeter on the ECU harness side
    The IGT terminal voltage on the connector, ie the IGT signal voltage, should be approximately 0.8V. If the measured IGT signal voltage close to 0V, should remove the igniter harness side connector, and then measure the engine start IGT terminal voltage; if the IGT signal voltage is still close to 0V, indicating that the ECU no IGT signal output, Electrical or its lines are faulty.
    B. Remove the distributor harness connector and measure the signal voltage output from the crankshaft sensor and the engine speed sensor when starting the engine. The value should be within the specified range. If the measured signal voltage does not meet the standard, then the sensor is faulty; if the measured signal voltage is normal, then the ECU or ECU to the distributor line is faulty.