WS6 Oxygen Sensors on Vehicle

Oxygen Sensors  


 The sensor is part of the emissions control system and feeds data to the ECU. The goal of the sensor is to help the engine run as efficiently as possible and also to produce as few emissions as possible.
­A petrol engine burns petrol in the presence of oxygen. It turns out that there is a particular ratio of air and gasoline that is "perfect," and that ratio is 14.7:1 (different fuels have different perfect ratios -- the ratio depends on the amount of hydrogen and carbon found in a given amount of fuel). If there is less air than this perfect ratio, then there will be fuel left over after combustion. This is called a rich mixture. Rich mixtures are bad because the unburned fuel creates pollution. If there is more air than this perfect ratio, then there is excess oxygen. This is called a lean mixture. A lean mixture tends to produce more nitrogen-oxide pollutants, and, in some cases, it can cause poor performance.
­ Th­e oxygen sensor is positioned in the exhaust pipe and can detect rich and lean mixtures. The mechanism in most sensors involves a chemical reaction that generates a voltage(see the patents below for details). The engine's computer looks at the voltage to determine if the mixture is rich or lean, and adjusts the amount of fuel entering the engine accordingly.
The reason why the engine needs the oxygen sensor is because the amount of oxygen that the engine can pull in depends on all sorts of things, such as the altitude, the temperature of the air, the temperature of the engine, the barometric pressure, the load on the engine, etc.
When the oxygen sensor fails, the computer can no longer sense the air/fuel ratio, so it ends up guessing. Your car performs poorly and uses more fuel than it needs to.

reference by http://www.howstuffworks.com

 WS6 Oxygen Sensors on Vehicle 

 
 Make   FORD    Model   KA     Year ...............

1.0 Locate Oxygen Sensor

1.1 Locate an oxygen sensor on your vehicle. Describe where it is located:
The oxygen sensor is located the top of the exhaust manifold in front of the engine.

1.2 How many wires for this oxygen sensor?   4

1.3 Record the colours for each of the wires at the sensor side of the connector (not the ECU side of the connector). Then list the use of the wires. Usually a black or blue wire will be the O2 sensor signal, Grey may be the sensor ground. Heater power and ground are often white. But there may be other colours. You may have to consult a wiring diagram.

Colour         Use or Purpose
White            heater +

White            heater -

Black            signal positive

Gray             signal ground

1.4 What type of Oxygen Sensor is this? (tick one)

Zirconia switching sensor? …√….

Titania switching sensor? …….

Broadband Air Fuel Ratio sensor? (one cell) …….

Broadband Air Fuel Ratio sensor? (two cell) …….

This worksheet is designed for switching type sensors only. If you have a broadband sensor, see your lecturer for another worksheet.

2.0 Back probe the Oxygen Signal Wire with a pin and connect to an oscilloscope. If you need help using the oscilloscope see your lecturer or other help sources. Check that you are connected to the Oxygen sensor signal: Run the engine and check that you are seeing a signal. Connected OK? Yes ……√…….

3.0 Watch and Record Oxygen Signal pattern at 2500 rpm. Let the engine warm up and enter closed loop so you see a normal cycling pattern. You may have to hold the rpm about 2500 for half a minute to go into closed loop. 

3.1 Freeze your pattern and draw or photograph it onto the graph below: Note the voltage and time per division or scale next to the graph.
 

 

3.2 How high does the voltage go?   0.908 v

3.3 How low does the voltage go?    0.107 v

3.4 What is the average voltage? (Some oscilloscopes have functions that will calculate the average for you. If not, just guess.)   0.500 v

3.5 How many “Cross Counts” does the signal have in 10 seconds? (One cross count is when it goes from high to low, or from low to high.) List here:  14 

3.6 If the signal is not cycling normally, describe what the signal does: 

OK  
4.0 Watch and Record Oxygen Signal pattern at Idle rpm. Let the engine warm up and enter closed loop so you see a normal cycling pattern. You may have to hold the rpm about 2500 for half a minute to go into closed loop. Then let the RPM come down to idle.      

4.1 Freeze your pattern and draw or photograph it onto the graph below: Note the voltage and time per division or scale next to the graph.

4.2 How high does the voltage go?   0.857 v

4.3 How low does the voltage go?   0.167 v

4.4 What is the average voltage? (Some oscilloscopes have functions that will calculate the average for you. If not, just guess.)   0.450 v

4.5 How many “Cross Counts” does the signal have in 10 seconds? (One cross count is when it goes from high to low, or from low to high.) List here:   6

OK

5.0 Make this Oxygen Sensor go rich by accelerating once or twice. (The fuel system should normally make the system go rich when you do a sudden acceleration.) Push on the accelerator quickly but don’t let the rpm go high enough to hurt the engine. (If you act like you will hurt the engine you will be asked to leave lab.) The signal should go over 0.85V.

5.1 Freeze your pattern as it goes rich and draw or photograph it onto the graph below: Note the voltage and time per division or scale next to the graph.

         

5.2 How high does the Oxygen sensor voltage go?  0.859 v

5.3 If this signal is not going high normally, describe what the signal does:
OK

6.0 Make this Oxygen Sensor go lean by doing a sudden deceleration. Gently run the rpm up to about 3,000, and let the RPM drop suddenly. The fuel system should make the system go lean on deceleration. The signal should go below 0.2V.

6.1 Freeze your pattern as it goes rich and draw or photograph it onto the graph below: Note the voltage and time per division or scale next to the graph.

 

6.1 How low does the Oxygen sensor voltage go?  0.131 v

6.2 If this signal is not going low normally, describe what the signal does:
OK

7.0 Measure the Response Time of the sensor. You want to know that the sensor can respond quickly to changes in the exhaust gas. The best way is to do a sudden acceleration, freeze the pattern, and measure how long it took the sensor to go from lean to rich.

     
7.1 Freeze your pattern as it goes suddenly rich from a lean condition and draw it into the graph below: Normally you want the voltage to go from below 0.2V to above 0.8V. in less than 100 ms. Note the voltage and time per division or scale next to the graph.

7.2 Measure how long the sensor took to go from lean to rich. Use the cursers on the scope if necessary. Record how long the sensor took here:  100 ms


8.0 Discuss how a normal Zirconium oxygen sensor works: draw a picture below to help show how it works?  

 The sensor signal shows the oxygen density of exhaust gases and the normal Zirconium oxygen sensor voltages go up(rich) and down(lean) repeatedly between 0 v to 1 v.

9.0 Discuss how good or bad this Oxygen Sensor is. What about it functions well or is faulty? Use detail and specific voltages in your discussion. Can it accurately tell the ECU how rich or lean the exhaust is?

 The output signal of oxygen sensor informs the vehicle’s ECU (Electronic Control Unit) whether the Air/Fuel Ratio is lean(below 0.2 v) or rich(above 0.8 v). Based on this, the ECU adjusts the amount of fuel injected into the engine to achieve an optimal air/fuel ratio.

   

WS7 Exhaust Gas Analysis (Petrol only)

WS7 Exhaust Gas Analysis (Petrol only)

Make  TOYOTA     Model CORSA    Year 1996

Exhaust Analyser should be warmed up and recently calibrated. When it’s time to start taking tailpipe readings, put the analyser probe into the tailpipe and install exhaust tube over probe to capture exhaust fumes. Make sure there is adequate ventilation. 

Note: make sure you fill out the “means: ............. segment to explain what that gas reading means. Example, if you are measuring HC, which shows us about misfire in the engine, and you had a low number like 28 ppm, you would say “shows low amount of misfire”, or “most of the fuel is being burnt.” But if the HC was high, like 340 ppm, you might say “There is a high amount of misfire” or “not all the fuel is being burnt.”  

1. With the analyser probe sensing normal air, what are the Four Gas readings? Record the amount and then what it means: 

CO 0.001%  means: control rich conditions
HC 12 ppm   means: higher HC means that unburn fuel remains in the exhaust gases.
CO2 0.00%  means: efficency
O2 20.9%  means: lean
2. Start the engine idling cold, and record the Four Gas readings:
Explain what is happening within the engine referring to the four gases:

CO 2.5%  HC 788ppm  CO2 12.6%  O2 5.15%

 When the engine starts with cold idle conditions, the CO increase to 2.5%. This means that rich mixture enters the combustion chamber. The HC also goes up significantly and unburn fuel remains in the exhaust gases. The CO2(efficency) is low and the O2 is high from the  inactive catalytic converter. 

3. When the engine has warmed up, record the Four Gas readings:
Explain what is happening within the engine referring to the four gases:
  CO 0.001%  HC 29ppm  CO2 15.01%  O2 0.40%

 When the engine is fully warmed up, the CO and HC noticablely decrease. This means that ideal mixture enters the combustion chamber. The CO2(efficency) is high and the O2 is low because the catalytic conver well operates for cleaning the emissions.

4. Run the warm engine at 2500 RPM, record the Four Gas readings:
Explain what is happening within the engine referring to the four gases:

CO 0.23%  HC 121ppm  CO2 15.10%  O2 0.32%

 When the warm engine is run at 2500 rpm, the CO and HC are more produced than the engine idling due to higher rpm with more emissions. However, the CO2 and O2 are still similar to idling condition.
   
5. At idle, run the mixture rich with extra propane, LPG, or carburettor cleaner, and record the Four Gas readings:
Explain what is happening within the engine referring to the four gases:

CO 0.96%  HC 224ppm  CO2 14.32%  O2 0.68%

 At idle, I made a disconnection of the vacuum hose in the fuel regulator for the rich condition. The CO increases to 0.96% which means the state of rich mixture. The unburn fuel is more produced due to more fuel injection.  

6. At idle, create a lean condition with an air leak or vacuum leak, record the Four Gas readings:
Explain what is happening within the engine referring to the four gases:

CO 0.029%  HC 470ppm  CO2 7.79%  O2 5.93%

 At idle, I made a disconnection of the PCV valve for the lean condition. The CO recovers the nomal condition. The unburn fuel goes up at 470ppm. The CO2(efficency) is reduced but the O2 increases significantly which means the state of lean mixture. 

7. Accelerate the engine, by blipping the throttle a few times (don’t rev too high anddamage the engine), and watch how the gas readings change. Record the Four Gas readings when the CO is highest:
Explain what is happening within the engine referring to the four gases:        
CO 2.5%  HC 434ppm  CO2 10%  O2 1.3%

From the sudden acceleration, the rich mixture is supplied into the combustion chamber. The CO and HC rise. The CO2(efficency) is reduced but the O2 increases slightly due to more fuel injection with more intake air.  

8. Disconnect one spark plug wire, ground it with a jumper wire, then record the Four Gas readings as the engine idles:
Explain what is happening within the engine referring to the four gases:       

CO 0.01%  HC 1033ppm  CO2 13.6%  O2 4.53%

 When the misfire is produced in a cylinder, the HC increases dramatically because the unburn fuel is created by the misfired cylinder. The O2 is also produced more from the air/fuel mixture of the misfired cylinder.

9. If you can get to it, disconnect the injector harness connector from one injector on an engine that has one injector for every cylinder: Record the Four Gas readings as the engine idles:
Explain what is happening within the engine referring to the four gases:

CO 0%  HC 55ppm  CO2 11.61%  O2 5.45%

 When the injector is disconnected, the HC is normal because the fuel does not injects into the intake port. However, the O2 increases due to the air is still supplied into the combustion chamber.  

10. Optional: Make other changes to the engine at idle, such as turning on the air conditioning or rocking the steering wheel. Note the change you made:
Explain what is happening within the engine referring to the four gases:

CO 0.009%  HC 18ppm  CO2 15.44%  O2 0.04%

 Overall, the emission is clean with proper values. However, when loads (air conditioning and rocking the steering wheel) are added, the rpm will go up. As a result , the CO and HC increase slightly with the rich condition.  

Return the vehicle to good condition and proper adjustment.
11. Explain the different readings you would get from a vehicle with a catalytic converter and a vehicle without one and why?

 I would get the differnt readings. If the vehicle does not have a catalytic converter the emission will be exhausted without any filtering. The catalytic converter helps reducing emissions with its chemical actions.

12. Explain what light off point means and what happens?

 When the temperature is hot enugh, the catalytic converter will clean the emissions with its operating temperature.

13. On lambda, 02 sensors why do they have 1,2,3,4 or 5 wires and what do these extra wires do?
 From two white heater positive and negative, the O2 sensor works correctly and increases responses with operating temperature when the engine starts with cold conditions. The black wire is a snesor signal positive which gives the state of exhaust gases to the ECU. The gray wire is a sensor signal earth.  

WS5 Scan Tool Diagnostics

WS5    Scan Tool Diagnostics

Make   TOYOTA              Model    SPRINTER           Year    1987

(Course: using a Scan Tool that communicates to the engine you want to test.)

Warning: Be careful working around engines and exercise caution to avoid injury.


1. Scan Tool Data


1.1 Find a vehicle which is appropriate for the scan tool. 

1.2 Connect the scanner, power it on, follow the instructions and input the correct vehicle information it asks for so you can view the data.


1.3 Find the data for the information listed on the next page. Turn engine on to idle. Fill in the letters used to label the information and the value of that data. (For example, engine load information may be found under MAP, with a value of 3.6, listed in volts) Note: not all vehicles will support all information, just find as much as you can. If the engine won’t run, input the information with the key on, engine off.
 
<><> <><><> <>

Type of information (PID = Parameter Identification)	Letters to describe it	Value of data	Units for data
	E.g. TPS		E.g. volts
Engine Load (how much air comes in)	Intake	29	kPa
Engine RPM	RPM	800	RPM
Throttle angle	TPS	0	%
Engine coolant temperature	ECT	85	℃
Intake air temperature	N/A	N/A	N/A
Fuel Injection opening pulse	FIOP	2	ms
Transmission select position	N/A	N/A	N/A
Vehicle Speed	N/A	0	km/h
Oxygen sensor(s)	N/A	LEAN	N/A
LEFT		RICH
RIGHT
Fuel Trim	N/A	N/A	N/A
Idle control	ISC	39	%
Power steering condition	N/A	N/A	N/A
Air conditioning condition	A/C signal	off	switch on/off
Exhaust Gas Recirculation (EGR)	N/A	N/A	N/A
Fuel Evap or Purge condition	N/A	N/A	N/A
Malfunction Indicator Light (MIL)	N/A	N/A	N/A
Barometric Pressure	N/A	N/A	N/A

2 Trouble Codes or Fault Codes


2.1 Find where the Codes are listed


2.2 Record any codes, and what system and condition they describe in the chart below (Example: might be code number 21, for Throttle Position Sensor, signal voltage too low) If there are no codes listed, put “none”.

Code number	System affected	Condition described
NO code

3 Lecturer put in Fault


3.1 Find your lecturer and have him create a fault under the hood (don’t look)


4 Record New Codes


4.1 Look up the codes now in the scan tool


4.2 Record the codes in the chart below. Also record what system is affected, and what condition is described.

Code number	System affected	Condition described
31	Air flow meter / VAC sensor	engine stop
22	Coolant temperature sensor	No signal, The ECU orders rich mixture all the time therefore, the engine RPM goes up.

5 Find What Data Has Changed
5.1 Look through the scan tool data to see what PIDs (Parameter Identification of system voltages) have changed. Which readings don’t make sense or don’t read what you would expect. Concentrate on the PIDs related to the codes.

5.2 Record the PIDs that have changed below:

Type of information (PID=Parameter Identification)	Letters to describe it	Value of data	Units for data
Engine Speed	RPM	875	RPM
Coolant Temperature Sensor	CTS	90	℃
Intake Manifold	Intake manifold	46	kPa

6 Visual Inspection to find fault
6.1 Do a visual inspection under the hood to find where the problem is. Use information from the code to know where to look for the problem and what type of problem to look for.


Describe problem you found:
 When the vacuum sensor is disconneted, the engine is not running.
7 Repair fault


7.1 Plug back in the connector, or repair problem found
 
7.2 Describe what you did:


  I have reconnected the vacuum sensor connector and then restarted the engine. The engine runs well with out any problems.

8 Recheck Data PIDs

Type of information (PID=Parameter Identification)	Letters to describe it	Value of data	Units for data
Engine Speed	RPM	825	RPM
Coolant Temperature Sensor	CTS	90	℃
Intake Manifold	Intake manifold	27	kPa

8.1 Recheck the data with the scan tool

8.2 Record the voltages for the PIDs related to the problem, to confirm they are back to normal

9 Clear Codes

Describe what you did to clear codes:

  I made a disconnection of the negative terminal or the engine main fuse for 30 seconds.  


10 Recheck for codes and record codes in system now:      

 When I recheck the codes from selecting D.T.C, there were no troble codes on the screen.

 

11 Discuss the importance live data when fault finding

 

It shows the state of the sensors from the live data values.
12 Explain the need for parameters when checking live data

when the fault is resolved, the live data will be rechecked with its parameters then the data should be compared to fault datas.

13 Discuss how a scan tool can aid you when fault finding  
   I can find the fault easily and although the vehicle is old or new, I can also check the state of a vehicle with various information.