Input Sensors & Actuators On Car

Injectors

Make - Toyota
Model - 4AFE

Discuss why we bother checking the voltage supply to the fuel injectors?

Because the injector is a electromagnet that lifts a armature to spray petrol into the combustion chamber or intake manifold or plenum chamber. If the injector dose not have supply voltage when the ECU switches to earth the electromagnet will not have any voltage so the armature wont lift.

If we find a lower voltage at the injectors than the battery, what can that mean? And how would injector operation be affected?

This could mean a faulty EFI relay or a bad earth somewhere this lower voltage would affect the injectors because the electromagnet would not get energised enough to lift the armature properly.

Wiring Diagram :

Reference Voltage at TPS sensor

What is the purpose of the reference voltage to the throttle position sensor?

To supply a set voltage to the fixed resistor so the movable wiper output voltage will change depending on its position on the fixed resistor from the supply end to the ground end.

What could cause problems so that there is not the correct reference voltage at the throttle position sensor?

There could be a loose connector plug or some dirt or grease in the plug.

Ground at TPS Sensor

TPS sensor ground voltage was 0.3v

What dose this tell you about the ECU earth or ground? Why is it important to measure it?

0.3v tells us that there is a good earth or ground at the ECU. IF this voltage reading was over 0.5v this would mean there is a bad earth and would result in the TPS sensor functioning incorrectly.

TPS Return/Output

Half open throttle with engine off 2.2v

Wide open throttle with engine off 3.8v

Describe hoe a TPS sensor works.

The TPS has a potentiometer which is a variable resistor. This has a fixed resistor that has a 5 v reference voltage supply. The fixed resistor has a movable contact the moves across the resistor and depending on which end of the resistor the contact is it will give a varied output voltage. On the sensor we tested at closed throttle was 0.4v half throttle was 2.2v and wide open throttle was 3.8v.

Discuss what type of sensor voltages should go to the ECU as the throttle opened and closed.

The sensor voltage should be a smooth steady voltage the increases as the throttle opens and decreases as throttle closed.

Decribe problems which could occur to prevent the TPS from sending the correct voltage to the ECU.

If the slider contact became fouled by grease or dirt this would cause a poor contact with the fixed resistor this would cause a incorrect voltage signal being sent to the ECU.

TPS circuit diagram.

Engine Coolant Temperature Sensor (ETS)

Back probe supply wire for ETS voltage with engine off and ignition on = 1.46v

After running the engine for two minutes we tested again and got 1v

Describe how an ETC sensor works.

The ETC has a (NTC) negative temperature coefficient variable resistor that resistance decreases as the coolant temperature increases. The ECU sends a 5v supply through a fixed resistor that is in series with the NTC, and because all the voltage must be used up in a series circuit the ECU can calculate the temperature of the coolant by how much voltage is needed to push across the NTC compared to the fixed resistor.

Describe how the ETC sensor voltage affects the fuel injection.

The ECU uses the ETC signal in part to determine how much fuel is needed.When the engine is cold the voltage signal from the ETC will be interpreted as cold engine and adjust air/fuel mix to suit the conditions.

Describe what could go wrong to create an incorrect voltage for the ECU.

If the plug connector to the sensor got contaminated by grease or dirt this could cause a resistance in the circuit resulting in a incorrect voltage being sent to the ECU.

Ground ETS

Back probe test on the ground wire to the ETS 0.001 this means there is a good earth. It is important to measure the earth or ground for the sensor because if there is a bad earth the voltage signal sent to the ECU would be incorrect and this would effect engine operation. If the ECU connector plug got dirt or grease in it or poor ground conection would cause a bad earth.

ETS circuit diagram

RPM Sensor or Crank position sensor (CPK)

 Back probe the signal wire for the RPM sensor with engine idle. 0.23v AC

Increase engine RPM 2500 =  0.45v AC

Return engine to idle speed and switch meter to DC this reading was 0.71v DC

Increase rpm to 2500 = 0.17v DC

Switch the volt meter to read at idle Hz = 38

At 2500rpm = 98 Hz

The best setting to show the RPM sensor working was Hz.

The RPM sensor on the engine we tested was inductive type with Ne and G signals. The G signal tells the ECU the standard crankshaft angle. The Ne signal tells the ECU the crankshaft angle and engine speed.

Describe how this type of RPM or crank sensor works.

The Ne generator has a toothed timing rotor or reluctor and a pick up coil. The pick up coil is connected to a fixed magnet. When the reluctor which is made from a magnetic material spins past the pick up coil and magnet it cuts through the coils magnetic field creating a alternating voltage.

Discuss how using different functions of your meter can help you to accurately measure the sensor output when you don't have a oscilloscope available.

This can help because you can check your different meter readings against each other and see if they are within manufactures specifications.

What can go wrong so the ECU did not receive the correct signal from the RPM or crank sensor.

If the ground shield around the signal wire were to perish a electrical interference could combine with the signal voltage resulting in a incorrect voltage to the ECU.

Manifold Absolute Pressure (MAP)

Back probe the MAP sensor plug and attach meter and record voltage at idle = 1.3v

Snap acceleration = 3.2v

Describe how the MAP sensor works to tell how much air comes into a engine?

The MAP sensor has a piezo resistive wafer thin silicon chip. When this chip is is distorted by changes in the intake manifold pressure. The resistance changes in relation to how much the silicon chip is distorted. There is a integrated circuit that converts the changes in resistance into a voltage signal that is then sent to the ECU.

Discuss how the readings above are correct or incorrect for this engine.

These readings are correct because at idle there is low pressure on the silicon chip which means there is not much deformation of the chip. This means there is a small resistance so a low voltage reading was recorded 1.3v this was within manufactures specifications. At wide open throttle there is high pressure on the silicon chip this causes a increased deformation resulting in a higher resistance and higher voltage signal. the reading we got was 3.2v this within manufactures specifications. below is a couple of diagrams that I got off blackboard that show the workings of the MAP sensor.

What could go wrong so the ECU did not receive the correct signal from the MAP sensor?

If the vacuum hose that goes from the sensor to the intake manifold had a kink in it this would result in a incorrect pressure on the silicon chip this wound end up giving a incorrect voltage signal to the ECU.

SENSORS (Off Car)

Throttle Position Seneor (TPS)

What type of TPS is this ?

 Linear.

Explain its internal operation and why your voltage changes.

The linear TPS has a variable resistor (potentionometer) which has a slide contact that moves across the resistor when the throttle butterfly moves. This gives a voltage of 0.5-1v when butterfly is closed at idle and then voltage increases as throttle buttefly opens to aprox. 4.5-5v at fully open.

Now connect a power supply to your sensor and test the voltage output at diffrent throttle angles.

Throttle angle :                                          Voltage output :

  fully closed 0°                                                      0.9v
        30°                                                                1.59v
        45°                                                                2.14v
        65°                                                                2.95v
        80°                                                                3.92v
  fully open 90°                                                      4.8v

TPS Throttle Position Switch

Place the ohm meter across the E and IDL pins and with throttle shut, check for continuity.

E - IDL throttle shut = 0.1Ω throttle open = 0.L

Place the ohm meter across the E - PSW pins and check for continuity when throttle is wide open.

E - PSW throttle open =  0.2Ω throttle closed = 0.L

Explain the internal operation of this sensor and why the resistance changes.

The resistance changes because the TPS switch has contacts that switch so at closed throttle you can maessure E - IDL resistance. but when contacts open you get 0.L the same thing happens with E - WOT with contacts closed you can meassure resistance but when they open you get 0.L

AIR FLOW/MASS SENOR (MAF)

What voltage did you get when you first powerd up the sensor without passing air over the sensor?

1.1 volt

How did the voltage change when air was passed over the sensor?

The voltage increased from 1.1v to 3.2v

Explain the internal operation of this sensor.

The (MAF) sensor has a power transistor that supplies voltage to a wheat-stone bridge. This has two temperature sensitive resistors one is a PTC and acts as a heating element the other is NTC resistor and acts as a thermistor, each is connected to another resistor. The PTC has a platinum hot wire and is connected to the inverting side of a differential op-amp and also sends signal to ECU. The thermistor is connected to the non-inverting side of the differential op-amp. When engine speed increases air flow increases cooling the thermistor and lowering its resistance this increases the voltage across the second resistor which suppiles the non-inverting side of the op-amp. This increases the voltage output of the op-amp which turns the power transistor more on so more current is supplied to thermistor heating it back up. The higher current is also supplied to the PTC resistor which sends an increased signal to the ECU.

Vane or flap airflow sensor/meter (AMF)

http://www.youtube.com/watch?v=cVDdOoHj-_I

Explain the internal operation and why your voltage changes.

The vane/flap is L shaped plate that has a measuring plate and a copmensating plate attached to a return spring. The incoming air deflects the mearsuing plate in proportion to the volume of intake air flow. The compensating plate moves in the damping chamber and prevents rapid movement of the measuring plate. The measuring plate is connected to a potentiometer which coverts movement of the measuring plate into a veriable voltage signal. A moveable contact on the measuring plate move across a fixed resistor that has a 5v referance voltage and a ground, as air intake increases the output voltage signal changes as the moveable contact moves across the fixed resistor. On the sensor we tested the voltage went from a higher voltage 4.53v at closed to a lower 0.45v at open.

Knock Sensor :

Connect the knock sensor up to an oscilloscope. Tap the end of the knock sensor and observe the wave form.

Explain why we are reading a voltage from this sensor when we are not supplying a voltage to it.

This is because the knock sensor has a piezo crystal element. When the element is destorted by vibration from the cylinder block caused by detonation it produces a small AC voltage.