Input Sensor and Actuators On-Vehicle

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

A. Voltage supply is needed to operate the injectors otherwise they can not open and close itself

Q.If we find lower voltage at the injectors that at the battery, what can that mean? and how would injector operation be affected?

A. It means that there may be bad connections in this circuit or high resistance in the wires to injectors. In this situation the injectors would not be opened fully to inject the proper quantity fuel to the cylinders

Circuit diagram for fuel injectors

Reference Voltage at TPS sensor

Q.What is the purpose of the reference voltage to the throttle position sensor?
A. To check that the correct voltage is going to the sensor to operate it correctly.

Q. What could cause the problems that there is not the correct reference voltage at the Throttle Position Sensor?
A. High resistance in the supply voltage wire or bad earth.

Ground at TPS sensor
Record the voltage on the meter 0.01V ( A good ground will usually read less than 0.05 V. Some manufacturers say 0.1 V)
Q. What does this voltage tell you about the ECU earth or ground? why is it important to measure it?
A.It tell us that the ECU is grounded and the circuit is closed. It is important because if it is not grounded then TPS sensor will not work and the engine will not work properly.
A. This tell us that the ECU is grounded. It is important to measure this voltage because we can see from this voltage whether ECU is grounded or not.

Q. Discuss what could go wrong so that the ECU earth or ground is not good?
A. If ECU earth is not good then ECU will compare TPS signal voltage wrongly with the reference voltage and hence effects engine performacne.

Q. Describe how a TPS sensor works?
A. When the throttle butterfly moves as opening and closing of throttle, the signal arm moves up and down on the carbon track. This signal arm measure the voltage over the carbon track according to the resistance of carbon track and then the signal arm send the signal to ECU to compare this voltage with reference voltage. After comparing and processing this signal voltage, ECU send back the new signal to adjust the throttle postion so it wouldn't effect the engine proformance.

Q. Discuss what type of sensor voltage should go to the ECU as the throttle is opended and closed?
A. As the throttle is opened, the signal arm moves up the carbon track and therefore decrease in resistance and hence increase in voltage. when the throttle is closed, the resistance is highest and voltage is very low at this position.
Q. Discribe problems which could occur to prevent the TPS from sending the correct voltage to the ECU?
A. Bad ground and the sludge deposite over the throttle which effect the opening and closing of throttle.

ECT (Engine Coolant Temperature) Sensor

Q. Discribe how an ECTsensor works
A. ECT sensor is a NTC type of sensor. As the engine worms up or coolant worms up, the voltage acorss its terminals goes down and hence this voltage is sent to the ECU for comparing with its referance voltage.

Q. Describe how the ECT sensor voltage affects the fuel injection output from ECU
A. After pocessing the sensor voltage, ECU controls the fuel injection output so that it wouldn't affect the engine proformance. It sends the signal to the injectors not to open for long time.
Q. Describe what could go wrong to create an inncorrect voltage for the ECU
A. It may heat up the engine which results in damge the engine, like cylinders cracking.

Q. what does this voltage tell you about the ECU earth or ground? Why is it important to measure it?

A. It tells us that ECU has good earth. It important because other wise sensor will not give us the wrong voltage output

Q. Discuss what could go wrong so that the ECU earth or ground is not good:

A. ECU will process wrong signal and return back wrong signal to other engine's signals and hence affect engine performance

Q. Describe how the MAP sensor works to tell the engine how much air comes into the engine?
A. There is a silicon chip in the sensor. Silicon chip changes its resistance with the changes in pressure. Change in resistance alters the voltage signal. ECU interprets the voltage signal as pressure and any change in voltage signal means there was a change in pressure. Thats how engine knows how much air comes into the engine.
Q. Discuss how the readings above are correct or incorrect for this engine:
A. Here we need to compare the intake pressure with voltage changes but we do not have facility here to measure these two things together. Voltage is decreasing with accelration of the engine. It means it might be in working condition.
Q. What could go wrong so the ECU did not receive the correct signal from the MAP sensor?
A. If ECU didn't receive the correct signal from MAP, the engine could either run lean or rich, depend upon the signal received by ECU

Q. Describe how the MAF sensor works to tell the ECU how much air came into the engine. Include what readings might be normal under different load conditions.

In above diagaram, the power transistor supplies voltage to wheat-stone bridge. The voltage is divided and dropped through to point A and B. As the engine revs up and the air flow increases and it cools the thermistor and lower its resistance. This means at point A the voltage goes up because more voltage is needed to drop across the second resistor. This increased voltage is then supplied to the non-inverting side of the differntial op-amp. Increasing its output which then goes to the base of the power transistor turning it on more and so supplying more current to the thermistor heating it back up to its previous temperature. This increasing current also flows through the platinum hot wire giving an increased signal to ECU.
Q. Discuss how the MAF readings above are correct or incorrect for this engine:
A. We did this experiment on Nissan Cefiro but it didn't have the manufactures' specifications in it. We when we scan it with a scaner, we couldn't find any error code up on the screen. From the above values of voltage, it seems that its working well as the voltage increases with more air going through it.
Q. What could wrong so the ECU did not receive the correct signal from the MAF sensor?
A. The hot wire may contaminated with crankcase ventilation oil fumes and form a sludge on it. This may effect the sensitvity of the thermistor and hence its resistance.

Q. Decribe how the IAT sensor works
A. The sensor has two-terminal electrical connector attached to either end thermistor element. It monitor the temperature of air entering the intake manifold by mean of a thermistors. It has the same resistance characterstics as the water temperature sensor. As the pressure and density of air changes with temperature, It sends the signal of intake air temperature to ECU. ECU then processing it for fuel correction program.
Q. Describe how the IAT reading affects the ECU outputs for fuel injection. Include how an incorrect input could affect the fuel injection and engine running:
A. As the air is more dense when cold, so the engine will run lean in this condition. IAT sensor sends the signal for this by mean of voltage variation to ECU. ECU then process it for fuel correction program and make the fuel adjustment accordingly so that the engine run in closed loop.
Q. Describe how the IAT sensor signal should change for different air temperature conditions:
A. IAT sensor has same resistance characteristics as water temperature. At high temperature it will send the low voltage to ECU and in cold condition when air is dense (more air going inside intake monifold), it will send high voltage to ECU.
Q. Describe what could go wrong to create an incorrect IAT signal for the ECU:
A. It will send worng signal to ECU and then the engine will either run lean or rich according to the signal received by ECU.
Diagram:

Diagram: