Sensors
Note: the term TPS can mean either throttle position sensor or throttle position switch Throttle Position Sensor (potentiometer) Potentiometer type sensors are composed of variable resistors that have a slide contact, which changes its position as the throttle butterfly moves.
A voltage is supplied to the sensor by the E.C.U. As the throttle position changes, the output voltage from the sensor changes, this in turn is recognised and a comparison made by the E.C.U to its memory. These sensors are adjusted by loosening the sensor mounting screws. (It is critical that you follow the manufacturer’s set-up procedure)
For example:
The idle position is recognised by the lowest voltage reading through the sensor but in contrast, the maximum power signal is recognised by the highest reading at the full throttle position of the sensor travel. It is important that both signals are correct.
Checking the Throttle Position Sensor
What type of TPS is this?
- This is a variable throttle sensor.
Explain its internal operation and why your voltage changes
- The voltage changes when the body butterfly opens, coursing the resistant to decree letting the car go faster, the variable throttle body sensor pics this up and sends a signal to the ECU saying the throttle is opening there for put in more fuel and air in to the combustion chamber to increase the speed.
- A throttle positon sensor (TPS) is a sensor used to monitor the position of the throttle in the engine.
- The sensor is usually located near the butterfly so it can sence the throttle value directly.
- There are usual 3types of wires one ground, 2nd to the ECU and 3rd Is the input,the voltage changes each time the wire back to the ECU increases because of the changing in the air flow
`Now connect a Power Supply to your sensor and test the voltage output at different throttle angles. NOTE: Always use a 5V supply.
| Throttle angle | Voltage output |
| IDLE | 0.74 V |
| 22.3c | 1.20 V |
| 45c | 1.79 V |
| 65c | 2.2 V |
| 75c | 3 V |
| 90c | 3.9 V |
Now plot your findings on a graph
Trottle Position Switch There is an idle position signal that is used mainly for fuel cut-off control and ignition timing corrections. The power signal is created at full throttle and is used for increasing fuel injection volume which in turn increases engine power output. Note there is no switching at part .   |
Throttle position switch detects throttle position at idle or full throttle by using switch contacts that are connected or disconnected as throttle position changes.
This type of switch can have two or three contact positions and is usually checked and adjusted using a multi-meter. Adjustment is made by loosening the mounting screws and rotating the switch assembly.
On - Off type throttle position switches can have:
Two position (three pin) or
Three position (four pin).
Testing the throttle position switch.
Note: PSW means power switch (WOT)
IDL means idle circuit
E means earth
Plot your findings on the graph
Explain the internal operation of this sensor and why the resistance changes
Manifold Absolute Pressure (MAP)
Wire up a map (manifold absolute pressure) sensor with a 5 V feed and earth. Measure the return voltage from the third wire. Using a mity-vac apply vacuum to the map sensor. Plot the voltage return in relation to the vacuum applied.
Dose the map sensor match the manufacture specifications, why, why not
Does a map sensor read vacuum or pressure?
This reads pressure..
Explain the internal operation of this sensor and why the output voltage changes
Air flow/mass sensors (MAF)
What voltage did you get when you first powered up the sensor without passing air over the sensor?
How did the voltage change when air was passed over the sensor?
Explane the internal operation of this sensor.
Vane or flap air flow sensor/meter (AFM)
Are your results within the manufacturer’s specifications, why or why not?
Explain its internal operation and why your voltage changes.
CTS (Coolant Temperature Sensor)
THw (Thermistor water)
ECT (Engine Coolant Temperature)
Suspend the engine coolant temperature sensor in a container of water as shown.
Temperature Resistance
(deg C) (ohms)
- 10 7,000 - 12,000
20 2,000 - 3,000
50 700 - 1,000
80 200 - 400
85+ Less than 200
On - Off type throttle position switches can have:
Two position (three pin) or
Three position (four pin).
Testing the throttle position switch.
Note: PSW means power switch (WOT)
IDL means idle circuit
E means earth
Plot your findings on the graph
Explain the internal operation of this sensor and why the resistance changes
- this sensor senses the amount of air flowing threw the engine.
- The resistance decreases as the throttle is opening, as the resistance decreases, more air is entering the engine.
- This is a switch therefor this is ether a open circuit or a closed cuircit. (Off Or On), when the angle turns a sertain degree the sensor switches it off (the reading in the multimeter is 0.00v) or if the switch is on( the reading is 0.0v) the ECU input wire sends this signal according to the airflow.
Manifold Absolute Pressure (MAP)
Wire up a map (manifold absolute pressure) sensor with a 5 V feed and earth. Measure the return voltage from the third wire. Using a mity-vac apply vacuum to the map sensor. Plot the voltage return in relation to the vacuum applied.
Dose the map sensor match the manufacture specifications, why, why not
- Yes, As I passed air over the sensor the voltage decreased, dependant on the amount of air passing through it. according to the manufactures specifications the map sensor is in good condition. when is reached 25Hz i had less than 4 volts on the sensor
Does a map sensor read vacuum or pressure?
This reads pressure..
Explain the internal operation of this sensor and why the output voltage changes
- The manifold absolute pressure sensor is a sensor inside the manifold to measure the changes in the manifolds pressure and make those changes in to a signal and send that signal to the ECU,wich then calculates the load on the engine. How this works is ,there is a silicon chip mounted inside the refferenc chamber.
- One side of the chip sensors collecting pressure(vacuum) ,the other-side of the chip is the pressuse to be measured. this silicon chip changes the resistenc with the change in pressure this is how the output voltage change.
- This is a switch type thermostat therefore it is ether on or off.
Air flow/mass sensors (MAF)
What voltage did you get when you first powered up the sensor without passing air over the sensor?
- 1.084V..
- As variable-presser is passed over the sensor the sensor picks density of the air and sends a signal to the ECU threw the ECU wire . the more dence the air gets the the bigger the signal back to the ECU gets bigger.
Explane the internal operation of this sensor.
- The MAF sensor converts the amount of air drown in to the engine into a voltage signal. this is nessesory because to determine how much fuel to inject, when to ignite the cylinder, and when to shift the transmit ion.
- There are two types of mass airflow sensors. in use./ 1st- the vain meter, 2nd Hotwire. nether can measures properly but with a additional sensor or two this can be read accurately.
- Both systems are used in fuel injection engines.
- Both the sensors designs output 90.0-5.0volts.
Vane or flap air flow sensor/meter (AFM)
Are your results within the manufacturer’s specifications, why or why not?
- Yes according to my observation the vane airflow meter is within the manufactures specification, in the specs angle: closed specification 1.6 volts _+ 0.5 volts, when i tested i got :0.681V.
- And at 90 degrees: spec 2 to 5 volts and i got a reading of 4.9 V.
Explain its internal operation and why your voltage changes.
- This sensor senses the airflow angle opening in the throttle body and sends a voltage signal to the ECU on the input wire, witch controls the amount of air entering the engine.
CTS (Coolant Temperature Sensor)
THw (Thermistor water)
ECT (Engine Coolant Temperature)
Suspend the engine coolant temperature sensor in a container of water as shown.
Temperature Resistance
(deg C) (ohms)
- 10 7,000 - 12,000
20 2,000 - 3,000
50 700 - 1,000
80 200 - 400
85+ Less than 200
Heat the water and check the temperature with a thermometer. Do not let the thermometer
touch the bottom of the hot container as this might damage the thermometer or give an
incorrect reading. Also check to see if there is any resistance to the body of the sensor it
should be OL(over load)
Graph of the readings
Graph of the readingsDoes the sensor meet the manufacturer’s specifications why or why not?
- Yes, because 20 to 50 degrees the temperature dropped by a KOhme, yet it stayed between 1KOhme-2KOhme.
- when the temperature reaches 80 degrees the resectenc stays between 100Ohme-300Ohme
What type of thermostat is this?
- This is a negative temperature sensor, (N.T.S)
Explane the internal operation of the sensor?
- This sensor senses the heat in the water, this activates the variable resister witch varries the current flow when the resistant verries according to the heat in the water., EG: when the resistance is Low the temperature is high.when the temperature is low there resistances high.
- then the sensor sends this information on the ECU wire it sends a signal back to the ecu wich then calculates how rich to run the engine to worm it up
Thermo Fan Switch
Suspend the engine thermo fan switch in a container of water as shown to heat the
sensor. Heat the water and check the temperature with a thermometer.
Do not let the thermometer touch the bottom of the hot container as this might damage the
thermometer or give an incorrect reading.
- I have measured the turminals on eachside and have ploted a graph of how this switch may work.
Does the fan switch meet the manufacturer’s specifications? Why or why not?
- Yes, the switch constantly increases the voltage by a little-bit. But as soon as the temperature goes above 92degrees the switch closes therefore this matches the manufacturer specifications..
Is this a thermistor?
- No, this sensor works as both a switch and a sensor, it sensors the heat for the time its meant to , as soon as the temperature hits a certain point the sensor urns off like a switch.
Explain the internal operation and why your resistance changes?
- As the sensor heats up, the resistance do not change by a lot. approximately by 1Ω.
- This happens because of the Bi-Metal inside. Bi-Metal is two metal plates inside placed next to each-other, what happens in-side is, when the two metals plates heat up they bend towards one side, at95 degrees it touches the other end of the switch witch gives me a reading "OL" (over-load) the switch coursing in to turn off.
ATS (Air Temperature Sensor)
THA (Thermistor Air)
IAT (Intake Air Temperature)
Connect an ohmmeter to the terminals of the sensor. Suspend the sensor in a container of
water to heat the sensor. Heat the water and check the temperature with a thermometer.
Note the resistance change..
Does the sensor meet the manufactures specifications? Why or why not?
- Yes, it dose, is the heat increases the resistence goes down gradualy.
- the resistence stayed between 1400KΩ to 400Ω therefor this sensor meets the manufactuers specifications.
What type of thermistor is this.
- Engine air temperature sensors. (this sensor is a thermistor.)
What do you observe about your results of the air and coolant sensors?
- The IAT sensors the air entering the engine. The engine computer needs these information to estimate the air density so it can balance. the air/fuel mixture, it works as a coolant sensor. the ECU applies the voltage to the sensor (usually 5Volts)threw the input wire back to the ECU then looks at the voltage signal it reads to calculate air temperature. The return voltage signal in the return wire will change in propotion to the changes in air temperature.
Knock sensor
-Connect the knock sensor up to an oscilloscope.
-Gently tap the end of the knock sensor and observe the waveform
-pic of the waveform on the graph below
Explain why we are reading a voltage from this sensor when we are not supplying a
voltage to it.
- The Knock sensor sensors the knocking in a engine and sends a signal to the ECU..
- inside is a "Piezoelectric" element. when this element shakes is produces a voltage signal thisis why we read a voltage reading we got in the graph..
- the Knock sensor is designed to allow the engine to run at the most stable timing without less were and tear as possible.
Oxygen Sensor.
Testing O2 sensors on the workbench.
Use a high impedance DC voltmeter as above. Clamp
the sensor in a vice, or use a pliers
or vice-grip to hold it. Clamp your negative voltmeter lead to the case, and the positive to
the output wire. Use a propane torch set to high and the inner blue flame tip to heat the
fluted or perforated area of the sensor. You should see a DC voltage of at least 0.6 within
20 seconds. If not, most likely cause is open circuit internally or leads fouling. If OK so far,
remove from flame. You should see a drop to under 0.1 volt within 4 seconds. If not likely
silicone fouled. If still OK, heat for two full minutes and watch for drops in voltage.
Sometimes, the internal connections will open up under heat. This is the same a loose
wire and is a failure. If the sensor is OK at this point, and will switch from high to low
quickly as you move the flame, the sensor is good. Bear in mind that good or bad is
relative, with port fuel injection needing faster information than carburetted systems.
ANY O2 sensor that will generate 0.9 volts or more when heated, show 0.1 volts or less
within one second of flame removal, AND pass the two minute heat test is good regardless
of age. When replacing a sensor, don't miss the opportunity to use the test above on the
replacement. This will calibrate your evaluation skills and save you money in the future.
Adjusting Reluctor Air Gap on Magnetic Distributor
Method
by Using a brass feeler gauges only, proceed to adjust the reluctor / pickup coil air gap
given specifications.
Signal Circuit: Refer to the signal waveform and compare.
Spin the distributor either by hand or in a synchograph machine.
Capture the signal waveform on a digital oscilloscope and record below (with time and
voltages. Show the peak to peak and peak voltage as well as wave time.
Formula:
Probe x volts / div x number of squares and increments
Describe the waveform using arrows and A, B, C etc. What is happening at different
points?
- When the distributer not rotating there is 37.7mV going threw it. As it rotates the voltage goes less, resulting in a low voltage reading. The faster it rotatates means there is more frequency and switches faster. The Voltage will stay the same..
- As shown on the graph were it starts the rotation forme, then the fall to CHA is the blade chopper cutting off the signal.
- this distrobuter rotates in half the time of the crank shaft, 1 rotation in the distributer i is equal to 2 rotations in the crakshaft
Hall -Effect Sensors
Note: always use 5 Volts unless instructed otherwise.
Wire up the distributor as shown in the wiring diagram. Connect an oscilloscope then spin the distributor and observe the waveform.
Hall- effect Distributor
Starting at the point where the voltage output changes, then turning the distributor clockwise until
the voltage changes again, note the degrees turned and the voltage obtained. Then repeat
until a full revolution is completed.
Optical distributor.
the distributor and observe the waveform
Red -12V
Practical task sheet
Now wire up your injectors to a power supply and listen to see if they click.
State any other engine problems that could give the same result as an injector not firing.
Describe the condition of all the injectors that you
Coil Test Results
Coil #1 Primary . .1.6Ohms .. Serviceable? yes
Coil #1 Secondary . 16.38Ohms.
Coil #1 Earth leakage test ..open cuircuit
Coil #2Primary . 1.3Ohms................ Serviceable? yes
Coil #2 Secondary O.L
Coil #2 Earth leakage test . Open cuircuit
Wasted Spark Coil Pack
Wire up the distributor as shown in the wiring diagram. Connect an oscilloscope then spin
the distributor and observe the waveform
Red -12V
Black- Earth
Blue –signal out
- What happens hear is that it the biggining of the black line going form one end to the other is the distributor signal reading.
- This distributor is like a switch , turns off and on.
- At the biging of the graph were the line first starts off is were the signal biggins.
- The first fall in the black line is were the choppers in the distributor cutting off the signal turning it off.
- There are 4 choppers, after all the choppers have gone pass the sensor, it is called one full rotation, this happens half the time in one full turn in the crankshaft.
- A hall-effect uses a steal chopper plate were optical uses inferd diodes.and inductive signals with referenc mark on the rotational crank pully.
Injector testing
Note:
Injectors from systems that use dropping resistors in the power feed to the injector can be identified from those that do not by their resistance value.
Common values:
With resistor 1.5 - 3.0
(Or with current control built into the E.C.U.)
Without resistor: 14.0 - 17.0
Practical task sheet
Checking Injectors off a Vehicle
Now wire up your injectors to a power supply and listen to see if they click.
State any other engine problems that could give the same result as an injector not firing.
- The fule line (nozzle) could be blocked.
- fuel could be enter-fearing with the injecters.
Injectors removed from the engine can be cleaned and tested in special test benches to
check for:
• Injector spray pattern.
Pattern should be an even cone shape without distortion or hard lines of fuel running
through it.
•Offset spray pattern.
Dirt or build up on the nozzle seat can cause the spray pattern to be offset to one side and
give poor atomisation.
• Delivery volume
Fuel flow must be compared with manufacturer’s specifications and there should be little
variation between injectors. The E.C.U. will open the injectors for the correct length of time but if there are restrictions within the injector they will reduce the flow and the related cylinder will run lean.
• Injector leakage. (Dribble)
Causes hard starting, especially when the engine is hot, and high fuel consumption. It is checked by applying full line pressure to the injector but not operating it. Fuel leaks past the seat causing drips from the nozzle. Most manufacturers state a maximum leakage factor of one drip per minute is acceptable.
Injector spray patterns
Test bench cleaning
This type of cleaning is very thorough as the injector can be inspected and tested at the same time.
These machines use a cleaning agent for flow and spray pattern calibration.
In some instances an ultra-sonic bath of caustic solution is used.
Ultra sonic cleaning is when the injectors are submerged in a bath of solution and a
current is applied to hold the injector winding open. The solution is vibrated at a very high
frequency and has a hammering action on the buildup of impurities inside the injector.
The test bench has a pump that pressurizes the test fluid to the same specified running
pressure as the vehicle, and allows for accurate fuel flow calibration and spray pattern
analysis as well as leakage checks.
(This procedure is more expensive but testing of injector can be carried out at the
same time)
Practical task sheet
Cleaning Injectors off a vehicle
When removing fuel injectors from the engine take care to:
- Relieve pressure in the fuel tank.
- cearful not to drop or damage the injector as it is really sensitive.
- Even removing the injectors is a timed and cearfull preceger that needs TLC as it cannot be rushed.
What are the manufacturer’s specifications in relation to:
Injector leakage none Drips per minute.
Injector flow rate 165 ML. per minute flow rate
Test results.
- No injectors require attention.
Analysing your results
Describe the condition of all the injectors that you
tested.
- these injectors are working fine except injector NO.1 is wearing out is the reading was jumping down as it was being tested, other than that the injectors are in good conditions all the readings are at 32 cc flow rate.
- the infecter no1 could be faulty due to number of reasons eg:spray pattern could be poor or the flow rate could be lower than the others...
Testing ignition Coils
To test the internal resistance of the primary and secondary windings, follow the diagrams
below.
Note: you will NOT be able to test the primary resistance of some wasted spark coil packs.
Testing ignition coils
Method
1 Obtain two different ignition coil configurations.
2 List all coil part numbers, voltage, internal resistance specifications where shown.
Coil Specifications
Coil# 1 No : C6R 500/12V Coil#2.No : CIT- 118/12Volts..
Coil# 1 Voltage . : 12V Coil# 2 Voltage :12V
Coil #1 Primary :3.0--5.0Ohms Coil #2 Primary :1.0--1.3Ohms
Coil# 1 Secondary :7.0--9.0KOhms Coil #2 Secondary :8.5--9.5KOhme
Remember
Always check for meter error and deduct that value off your final reading
( most important when using the 0 - 200 ohm scale )
3. Obtain a multimeter.
4. Carry out tests and record your findings.
5. Turn the meter rotary switch to the 200 ohm position, touch the positive and negative
leads together and note your default error.
6. Carry out tests and record your findings
Coil Test Results
Coil #1 Primary . .1.6Ohms .. Serviceable? yes
Coil #1 Secondary . 16.38Ohms.
Coil #1 Earth leakage test ..open cuircuit
Coil #2Primary . 1.3Ohms................ Serviceable? yes
Coil #2 Secondary O.L
Coil #2 Earth leakage test . Open cuircuit
Wasted Spark Coil Pack
Note: That if the coil you are testing is off a four cylinder engine you will only can check
two secondary windings, also if the ignition module is incorporated within the coil you will
not be able to test the primary windings
Coil #1 Secondary .....
6.94 kOhme |
Coil #2 Secondary ...
6.90 k ohms |
Coil #3 Secondary ...
6.93 k ohms |
Coil #1 Primary ........
6.95 k ohms |
Coil #2 Primary .......
6.93ohms |
Coil #3 Primary ......
5.95 ohms |
Testing Ballast resistors
1 Obtain 2 ballast resistors with different part numbers
2. List part numbers and resistance specification(s)
3. Measure the resistance of the resistors
Specifications
Ballast resistor 1 No.. .
BR3
Ballast resistor 2 No .... BR1
Ballast resistor No 1 ohm spec
1.5 -1.7
. Ballast resistor No 2 ohm spec 0.9-1.1
Measured Resistance Values
Ballast resistor No1 measured ohms 1.7 ohms Serviceable
Ballast resistor No 2 measured ohms 1.6ohms
Measuring Current Draw and Voltage Drop
Standard Single tower coil
1. Wire up a ballast resistor in series with your coil primary winding values as shown in
the following diagram.
2. Connect an ammeter in series and note the current draw.
3. Measure and note the voltage drop across the ballast resistor.
4. Measure and note the voltage drop across the coil primary.
Current draw 4.58 A
Coil calculated Voltage Drop=2.63v
Coil measured Voltage Drop 2.25v
Ballast resistor calculated voltage drop =856v
Ballast resistor measured voltage drop 8.20v
Wiring up ignition systems
Warning: Ignition coils create high voltage. It can be dangerous, so avoid getting
too close to ignition parts when engine is running. Make your connections when the
engine is off, and then keep your distance when the engine is running. Even some
primary voltage is high enough to stop a “Pacemaker”.
Warning #2: Don’t ground a coil for more than a few milliseconds or more than 50%
duty cycle. You can overheat the transistor or melt the inside of the coil. They will
go bad!
Wire up an ignition module using a function generator to trigger the module.
Have a coil and spark plug in the circuit so the spark plug can fire
Idea of how this looks like.
