WS3A

TPS (linear)
This TPS oscilliscope pattern is showing that the engine has started accelerating smoothly from idle. The TPS works by supplying a 5V reference to the potientiometer this read by a 'wiper' which connects with a different part of the potientiometer depending on how far the throttle pedal is depressed.
My theoretical fault is there is resistance in the earth wire.
For example the potientometer is 10k ohms, the resistance in the ground wire is 3k.
The throttle is at halfway.
Calculations.
R1=5000 R2=5000 R3=3000 RT=13k
5V/RT=0.000348 x R1=3.08 5-3.08=1.92
1.92/R2+R3=0.000385 x R2=1.925
1.92+1.92=3.84
5-3.84=1.16(R3)

So the signal sent to the ECU would be 3.84 for half throttle, but really the proper voltage for half throttle would be 2.5V.
As the ECU does not know any better it will adjust the air/fuel mix for a higher,roughly 2/3 throttle instead of half, which will cause the engine to run rich, which will effect performance and fuel efficiency.


IAT
The IAT and ECT work the same way. Both the sensors are NTC thermistors, this means that when the temperature increases they will decrease in resistance. It can range from 24000 ohms to 200ohms, all depending on the temperature.
In this picture the IAT sensor is being warmed up, as this happens it is slowly decreasing in resistance.

The ECT and IAT work by voltage drop. There is a 5Vsupply, followed by set resistor which is in series with the sensor. The ECM is able to calculate the temperature by reading the Vd across the set resistor. The set resistor will change in Vd as the sensor warms up. When the sensor is cold the set resistor will have less resistance, giving it a low Vd. As the sensor warms up and the difference in resistance is reduced the Vd will decrease over the sensor and increase over the set resistor. As this continues the set resistance will become greater that the sensors resistance and will have a large Vd across it. Using this Vd the ECM can tell the temperature.
If there was a resistance in the ground wire this would cause a fault which would mean the Vd over the set resistor would not be accurate as it would b
e Vd across the extra resistance also.

eg.
4500 ohm set resistor, and the temperature is 40C, so around 1100 ohms. VS=5V
4500(R1)+1100(R2)+400(R3)=6000(RT)
Vs/RT=0.000833
R1 x 0.000833=3.74
Vs-3.74=1.26
1.26/R2+R3=0.00084
R2 x 0.00084=0.924
3.74+0.924=0.336
R3 creates a 0.336 Vd.
So the set resistor is Vd 3.74 but it should be 4.014(did the same calculations for a normal reading), this will give the ECM a inaccurate reading.



ECT
The IAT and ECT work the same way. Both the sensors are NTC thermistors, this means that when the temperature increases they will decrease in resistance. It can range from 24000 ohms to 200 ohms, all depending on the temperature.
On this ECT sensor, at 20C it was around 2.7k ohms and as it warmed up the temperature reached 100C at 200 ohms.
If the set resistor (R1) is 20k ohms, the sensor is at 70C which is 400 ohm(R2)
There is a resistance in the ground wire of 8k ohms(R3).
R1+R2+R3=28.4k ohms (RT)
5V/28.4k=0.000176 x R1=3.52Vd
5-3.52=1.48
1.48/R2+R3=0.000176 x R2=0.7+3.52=3.59
5-3.59=1.41R3

As the voltage drop is lower of R1 than it should be, the ECM receives the wrong reading which effects the performance of the engine as they ECM will think its colder than it really is.

MAP
This oscilliscope pattern is showing me that there is little pressure going through the intake manifold. So that means the engine is idling, and at WOT the engine would show 5V as the pressure increases. The way the voltage is increased by pressure is that there is a reference chamber of pressure, a known pressure. This is seperated by a silicon chip, to the air pressure of the intake manifold. When the pressure increases the silicon chip changes its resistance which effects the output voltage.


Calculations
R1=14k ohms
R2=7k ohms
R3=6k ohms
R4=10k ohms
R5=19k ohms
RIN=2k ohms
RF=5k ohms

A= R1+R2+R5=RT1 (40K)
5V/40K=0.000125 x R1=1.75Vd at R1
5V-1.75V=3.25 at point A

B=R3+R4+R5=RT2(35k)
5V/35k=0.000125 x R4=1.428exp-4 x R4=1.428Vd at R4
5V-1.428=3.572V at point B

RIN
B/Rin=0.001786

MAF
The MAF sensor is used to measure the amount of air(mass).
At A the engine is accelerating hard WOT, increasing the mass airflow.
At B the car is decelerating to about half throttle.
At C the car is accelerating smoothly up to WOT.
At D the car is off the throttle, but the engine is still slowing down which is still drawing air in.
At E throttle is blipped increasing the air flow for a split second.

Calculations
Platinum wire=R1=34K Ohms
B-earth=R2=15k Ohms
Bad earth=R3=58K Ohms
RT=107K Ohms
5V/RT=4.672exp-5
R1 x 4.672exp-5=1.588
5-1.588=3.412V output at B

As there is a big resistance in the earth circuit, it draws voltage away from the lessers resistors, R1 and R2 and uses most of the voltage over R3. This effects the voltage at B as there would be less Vd across R1 as the voltage is needed down at R3. So there would be a higher reading at B.

WS3 Oscilloscope patterns

TPS(switch)
With the engine start the idle circuit is on to keep it running at the optimal air/fuel mix. As this is not a sensor but a switch, the ECU will not change the air/fuel mix until the switch changes to the WOT circuit. This will not happen till the throttle is depressed to 88degrees, at this point the switch activates and the WOT circuit kicks in, while the idle circuit stops. This tells the ECU that the engine is at needing an increased air/fuel mix so it can accelerate faster.

Oxygen Sensor
This pattern is showing the O2 sensor in closed loop. Open loop would be when the O2 sensor is not active, everytime you turn your car on the O2 is in open loop until it warms up to operating temperature. Closed loop is when the O2 sensor is cycling the air/fuel mix to evenly burn. It does this by sending its signal to the ECU which adjusts the air/fuel mix accordingly. When the air/fuel mix is lean it shows little voltage around .2V and when running rich its around .9V.



Hall Effect distributor
A=This is the dwell time
B=This is the firing time
C=This the peak voltage
The hall effect distributor works by passing a crystal by a magnet.
This means the electrons in the crystal are moving perpendicular to the magent. That then causes the electrons to get pulled to one side, giving a difference in voltage, which is then amplified by an op amp, which turns on the transistor.


Rpm sensor
This is the Rpm sensor, this is really showing the magent in the distributor at work. As the pole peice approaches the magnet, the voltage starts to increase as the air gap is getting smaller.
When the air gap is at its smallest the magnetic field is at its strongest at has fully saturated the trigger coil. As the pole peice or reluctor wheel moves away from the magnet, the magnetic field induced in the coil collapses and sends a negative voltage( a voltage in the opposite direction).
Then the next pole peice starts to come round and the cycle continues...

Injector pulse
The pattern us showing the injector being opened and closed. In the first square, this is showing the 12V supply. In the second square you can see the voltage drop to almost 0 as it is earthed, this is when the injector is open. In the fourth square the injector is turned off, this creates a back emf, in some cars this is used to charge the capacitors. In the 5th square, this shows the back emf fading as the injector returns to its normal 12VS.
If this injector pulse was faulty, this could effect the fuel/air mixture. If the injector stayed open to long it would let to much fuel though. This would flood the cylinder and cause the engine to run rich. This would then produce bad emissions and also reduce the power of the engine.

MAP(Manifold absolute pressure sensor)
This is a picture of a map sensor, while it was at idle. If the diaphragm had been damaged, it may not reach its max or min voltage. This could effect the output voltage to the ECU, which then is using the wrong information to run the car, which would obviously cause the car to become rich or lean. The higher the voltage the higher the pressure. So if the car was at idle like shown, it would raed around .8V-1V. At WOT the voltage would read at 5V.

Alternator Output
This pattern is showing that the AO is working correctly, as it is putting out 14.6V. If this was a faulty alternator, we would be able to see a lower voltage. Also if faulty the alternator would put out voltage spikes which you would be able to see with the oscilliscope. This is the alternator output, this shows that the alternator in my car is putting out 14.5V while it is running. If the alternator belt was slipping, it would not produce the voltage needed to charge the battery and run the some systems on the car.