WS3

Oscilloscope Patterns to Capture

TPS sensor

At point A the throttle is wide open which i set the oscilloscope voltage 1V per division, the throttle is wide open which is nearly 4V. At point B the throttle is closed  the signal arm point the lowest part of carbon track, at this stage the resistance are high, the output signal was o.4 at idle.At point C is same as point B.The voltage goes up when the throttle, usually close and open voltage is 0.5V to 5V in the sensor.

If the power supply from the ECU is unstable will case the voltage signal from the TPS incorrectly.

damage carbon track, corrosion of electrical connection, poor grounding terminal and wiring will change the total resistance in the circuit. so the different voltage will signal to ECU.

Higher output signal at idle will make the ECU to get wrong, the ECU will think that TPS is at half open throttle position.

At point A, The engine is just starting and running at cold, at this stage cold temperature, high resistance in the thermistor, thus higher voltage drops across the thermal resistor and ECU will get high output voltage signal, At point B the engine  warm up and resistance in the thermistor goes down and lower voltage drop signal  was sent to ECU.

Poor connection, damage terminal, faulty wire, bad grounding will make the ECT sensor operate incorrectly.

Corrosion of electrical connection, worn terminal and poor grounding from ECT to ECU will change the total resistance in the circuits, this will alter the output signal and not function properly. For example, ECT sensor consist of a thermal resistor of 3kohm at cold temperature and anothe constant 5kohm resistor inside the ECU which is connected with the ECT circuit, the ECU will receive about 1.8 output signal at cold temperature. If poor grounded add another 10kohm resistance into the ECT circuit, the output signal will become 3.61V, this make the engine coolant temperature is colder than normal and send the wrong signal to ECU.

If the faulty ECT send 3.61V to ECU, ECU will think that ECT temperature is colder than normal, so more fuel than normal cold start is injected into combustion chamber then engine will consume more fuel than normal.

IAT sensor

IAT Sensor

This sensor is not much different with engine coolant temperature. At point A, the air temperature is cold about 2.1V. At point B, the air temperature getting hotter because the engine has warn up.

Broken electrical connection damage terminals, damage in the wiring, corrosion of electrical connections and terminals and poor grounding, incorrect voltage supply will change the voltage drop across the thermal resistance and alter the output signal.

Damage terminal and broken connection will cause the IAT open circuit. Damage and corrosion on wire connection from IAT to ECU will change the total resistance in the IAT circuit. this will change the voltage drop across the thermal resistor and output signal to ECU. For example total resistance in the IAT circuit is 5Kohm, if corrosion on wiring cause the total resistance become 10kohm with 5V supply the current flow through the IAT will drop from 2V to 3.5V. Also extra resistance in the circuit will cause the IAT sensor malfunction.

If IAT sensor is not function properly, ECU will delivery incorrect amount of fuel when the air temperature is cold. faulty IAT sensor will affect the advance timing for cold start because cold air is more dense and contain more oxygen, thus repuire a richer mixture to achieve proper air/fuel mixture.

Oxygen sensor

At point A, the oxygen sensor generate about 0.2V, because the oxygen level is high in the exhaust and did not combine with the fuel, this mean air fuel mixture is lean.At point B, the voltage signal is about 0.7V, this mean there is little unburned oxygen in the exhaust and air fuel mixture is rich. when ECU receive a lean signal ( point A) from O2 sensor, it rich the fuel mixture and the O2 sensor output voltage will go up to point B. At point B, O2 sensor sense the mixture too rich and tell the ECU inject less fuel. This action keep continuity to adjust the engine fueling.

Injectors (petrol)

At point A, the injector is off, so we have supply voltage of 12V when the transistor receive signal from the ECU and ground the injector or switch ON the injector, the available voltage become zero, At point B, when the ECU turn OFF the injector, magnetic field in the solenoid collapse and generate back EMF, this show at point C. At point D the peak voltage of the back EMF. Point E describe a supply voltage and the injector is in OFF position. Point B also show the pulse width and period of an injector switch ON or grounded.

RPM( Hall digital crank or distributor)

At point A, firing period, on the steal chopper plate is passing through the magnet and hall integrated circuit, there was nothing was blocking the magnetic field, so the magnetic field able to pick up by the hall integrated circuit and generate a small current or voltage to op amp and ground the transistor, thus the output voltage in low and the ignition is firing. At point B, dell period, blade block the magnetic field, so the hall integrated circuit unable to pick up any magnetic field and the transistor is not ground, thus we have supply voltage of 5V and the ignition is in dwell period.