Input sensors and Actuators On-car

Make...toyota......

Model......4A-FE......

the voltage to the fuel injector is 14.49v

-We check the voltage supply to the fuel injectors to make sure there is no bad connection, high resistance in the circuit and the injectors circuit are opening or closing.The voltage supply to the injector should be enough to operate, otherwise it can cause the injector by not sparying properly.

-If we find lower voltage at the injectors than at the battery, this could be due to high resistance in the circuit, bad connection. it will effect open time of injectors, unnecessary fuel will enter to the cylinders.

There are two types of (TPS) sensors, one is a switch and another potentiometer or linear resistor type.The throttle position sensor (TPS) is used with feedback carburetion and electronic fuel injection (EFI) to inform the computer about the rate of throttle opening and relative throttle position.

High resistance in the copper wire or poor connection from ECU in the wire could cause problems so that there is not the correct reference voltage at the throttle position sensor. Also ground wires can cause problems, good ground voltage drop reading is usually lower then 0.05v.

Ground at TPS sensor

Ground wire voltage is 0.02V

If we have a bad ground or bad connection at the battery terminal or high resistane on the ground circuit, it can effect the output signal fo the sensor, that's why ground wire is also important.

It could be losing connection at the ground, the pin is not touching properly and problem in wiring.

Throttle Position Sensor return/output:

The reading from the mete is 0.5V (The ignition on)

Half throttle open position reading is 2.4V

Full throttle open position reading is 3.9V

Slowly open the throttle from the closed position to the full open position and the meter reading slowly increase with no sudden jumps or in the signal. ok!

I got the reading from green wire.

A TPS sensor works like a potentiometer, sending voltage signals to the computer to let it know how far the throttle have opened, as the throttle accelerator pedal moved, the signal voltage of the TPS also change. At closed throttle position, the signal of the TPS is low. At the throttle valve opens, the signal voltage increases so, at fully open throttle, the voltage should be less then 5V.

A fault TPS sensor can confuse the ECU causing the idle to be hunting, engine light will be on and hesitate while accelerating.

Throttle Position Switches:

Idle wire: Colour: Black

Volts at idle: 0.08V

Volts apart throttle or open throttle: 10.70V

Wide open throttle wire colour: Black

Volts at idle or part throttle: 10.24V

Volts at open throttle: 0.00V

Because the ECU will be monitoring the voltage signal received from the TPS sensor whcih can determine the fuel delivery required, so at different throttle positions the ECU would act as an injector difference of the fuel, so that the engine is running with a good quality of fuel/ air ratio – lambda which is 14.7:1.

ECT (Engine Coolant Temperature ) Sensor

The reading is 3.59V with the ignition on but not starting engine.

The engine is at normal operating temperature, it was cold and that is the right temperature of the engine.

Start the engine and warm up for about 2 minutes and the voltage of the ECT sensor is 2.67V

Yes, with the cold engine reading is 3.59V and with the warm engine reading is 2.67V.

How an ECT sensor works?

An ECT is device that change resistance as temperature change. There is a thermistor inside the sensor. The ECT( thermistor ) is a negative temperature coefficient sensor which means when the temperature goes up resistance and voltage goes down. The ECT works by changing it's internal resistane according to coolant temperature.

The ECT sensor receives 5V reference  voltage from the ECM. When the engine is cold, the ECT will send a high voltage to ECU, so the ECU makes the injector squirt more fuel into combustion cylinder. when the engine is heat up, the signal voltage from the ECU will be low and ECU will control the injector to shorter and less fuel into cylinder. 

If ECT sends an incorrect voltage for the ECU can cause a lean misfire or even no start on cold engine because ECU will control the injector to spary less fuel into combustion cylinder.

Ground Coolant Temperature Sensor

With starting engine the voltage on the meter is 35.5mv

This voltage 35.5mv tell me a good ground. it is important to measure it because we can see the ground voltage is suitable or not (A good ground will usuall read less than 0.05V. ( some manufacturers say 0.10V).

In this picture ECU ground is not good, the ECT sensor ground connected to ECU, if the ground is not good  the circuit is not complete and there is noly one refrence voltage.

RPM sensor or Crank Position Sensor (CkP)

The reading (AC volts) is 3.7V with the engine idling.

With increase engine RPM TO ABOUT 2500rpm, the reading is 7.2V

The reading (DC volts ) is 0.5V with the engine idling.

With increase engine RPM to about 2500rpm, the reading is 1.2V (DC)

The reading (Hz) is 466.4Hz with the engine idling.

The best showed if the RPM sensor was working HZ

Inductive sensor type of RPM.This type of sensor consists of a permanent magnet and pick up coil. The sensor is mounted close to crankshaft. As the crankshaft move on AC voltage pulse is induced in the pick up coil, the crankshaft rotate faster, more pulse are generated and ECU will determine the speed base on the number of pulse produce. 

I think there is only two functions, AC volt function of multimeter tells us how much voltage it generates for every tip passing the sensor magnetic pick up and Hertz tells us how fast it's rotating, as if speed of the shaft increased it increased frequency of rotation, so it start to rotate faster and get more revolutions per minute.

If the ECU did not receive the correct signal from RPM or Crank sensor, it can cause  short circuit, loose connection and  faulty signal converter.

MAP or MAF sensor

I turned on the ignition but no start the engine and checked the reading with the meter it was 1.83V. With the engine idling the reading was 0.6V.

With short acceleration of the engine the reading was 28.4mV.

Inside MAP sensor there is a silicon chip which changes resistance with different pressure inside intake system and this changes output voltage to ECU. When the engine is going hard, intake vacuum drops as the throttle open wide and the engine sucks more air, which requires more fuel to keep the air/fuel ratio in balance.

The readings are correct for the engine, due to the MAP delivered the voltage signal to ECU about 0.6 when the engine at idle. If the silicon chip is damaged, poor connection can effect the output voltage and send the wrong signal to ECU and also the vacuum hose attached to the sensor should be in good condition.

Incorrect signal from the MAP sensor sends the wrong signal to the computer can disrupt fuel consumption and affect engine performance.

IAT (Intake air Temperature), ACT (Air change temperature), or MAP (manifold air temperature sensor

The reading was 12.3 with the igniton "on"

This  reading is more than the reading i had for the ECT

This shows us the IAT sensor is colder than the ECT sensor

The intake air temperature sensor let  the computer know how hot or cold the incoming air is. The computer will then adjust the amount of fuel being injected, as well as make minor adjustments to timing based on that reading.Most air temperature sensors are negative temperature coefficient thermistor with high resistance the they are cold,but the resistance will drop as they heat up.

IAT reading will affect the ECU outputs for fuel injection depending on the intake air temperature as the engine heat up incoming air.The incorrect input can affect the computer sending that incoming air is warmer or colder than it  is , causing it to inject more fuel and advance the timing a tad.

If the air temperature is cold, the resistance in the sensor should be high and the voltage drops across the resistance is high then this voltage will send to ECU and the ECU will control fuel injector delivered more fuel into combustion cylinder. As the temperature is hot, the resistance should be low and ECU will control fuel injector delivered less fuel into combustion cylinder.

poor electrical connections at the sensor. A loose or corroded wiring connector can affect the sensor’s output and create the incorrect temperature and send the wrong signal to ECU.

Camshaft Position Sensor (CMP)

The readings in the different settings

DC volts:124.2mv

AC volts:1.543V 

HZ volts:24.32 Hz

% Duty cycle:82.3%

The AC voltage is good to show the CMP, due to the camshaft position sensor (inductive type) which generates AC voltage.AC voltage will move between 0.3-1 AC voltage, AC voltage increases will engine RPM, so the faster the engine crank, the higher the AC voltage.