1.0 Locate Oxygen Sensor
1.1 Locate an oxygen sensor on your vehicle. Describe where it is located:
1.2 How many wires for this oxygen sensor? 3 wires
1.3 Record the colors 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 colors. You may have to consult a wiring diagram. Black for signal, white for heater and other white for ground.
1.4 What type of Oxygen Sensor is this?
This type is Zirconia switching sensor working on 0.1-1V
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 it is.
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? 0.7V
3.3 How low does the voltage go? 0.02V
3.4 What is the average voltage? (Some oscilloscopes have functions that will calculate the average for you. If not, just guess.) 0.45V
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: 2
3.6 If the signal is not cycling normally, describe what the signal does:
Not cycling normal. It's still working well but not as I expected.
I would like expected the signal would be like the picture below:
Reference:
http://www.auto-facts.org/automotivescantool.html The signal as above running rich roughly 0.8V-0.9V and lean 0.1V-0.2V. And the same amplitude and frequency.
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? 0.8V
4.3 How low does the voltage go? 0.02V
4.4 What is the average voltage? (Some oscilloscopes have functions that will calculate the average for you. If not, just guess.) 0.4V
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: 1
4.6 If the signal is not cycling normally, describe what the signal does:
Not cycling normal. The pattern look like going down little bit before revv down. Should be the pattern curve down smoothly.
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? 0.8V
5.3 If this signal is not going high normally, describe what the signal does:
I revv the engine 3 times make the engine running rich, output amplitude the pattern not really smooth, even that what we would be expected.
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? 0.13V
6.2 If this signal is not going low normally, describe what the signal does:
The voltage nearly 0V, looks like normal or good sensor, lower than 0.2V. Will jump back to previous voltage after few second.
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 cursors on the scope if necessary. Record how long the sensor took here: 50ms.
Discuss how a normal Zirconium oxygen sensor works: draw a picture below to help show how it works?
Zirconia oxygen sensor is an impervious tube-shaped zirconia (zirconium oxide) element with a closed end and is coated externally and internally with porous metal electrodes, typically platinum. Above temperature 400°C, this sensor becomes an oxygen ion conductor, which results in a voltage being generated between the electrodes. The voltage is dependent upon the differences between the partial pressures of the oxygen in the sample and the oxygen in a reference gas (generally air).
Thus, with air on both sides of the cell, the output is zero. The reference electrode is negative with respect to the sample electrode for sample concentrations of oxygen higher than that of air and positive for concentrations less than that of air. Depending on the application either the internal or external electrode can be used as the reference. The output voltage is processed electronically to provide signals suitable for display or for process control purposes.
Reference:
http://www.hitech-inst.co.uk/pdfs/technical/oxygen_sensors.pdf
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?
I would say this is not really bad and far from good below than average. This O2 sensor still can read and give the signal to the ECU not even than I expected because have an interference and not give us the pattern smoothly.
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