Oxygen Sensor Information
In response to several requests for more information about Oxygen (O2) sensors, perhaps the following information will help. Comment:
These procedures are only for self powered conventional sensors. Some very new cars are using a different style sensor that is powered. *Many* Oxygen sensors are replaced that are good to excellent. *Many* people don’t know how to test them. They routinely last 50,000 or more miles, and if the engine is in good shape, can last the life of the car.
What does the O2 sensor do?
It is the primary measurement device for the fuel control computer in your car to know if the engine is too rich or too lean. The O2 sensor is active anytime it is hot enough, but the computer only uses this information in the closed loop mode. Closed loop is the operating mode where all engine control sensors including the Oxygen sensor are used to get best fuel economy, lowest emissions, and good power.
Should the O2 sensor be replaced when the sensor light comes on in your car?
Probably not, but you should test it to make sure it is alive and well. This assumes that the light you see is simply an emissions service reminder light and not a failure light. A reminder light is triggered by a mileage event (20-40,000 miles usually) or something like 2000 key start cycles. EGR dash lights usually fall into the reminder category. Consult your owners manual, auto repair manual, dealer, or repair shop for help on what your light means.
How do I know if my O2 sensor may be bad?
If your car has lost several miles per gallon of fuel economy and the usual tune up steps do not improve it. This *is not* a pointer to O2 failure, it just brings up the possibility. Vacuum leaks and ignition problems are common fuel economy destroyers. As mentioned by others, the on board computer may also set one of several failure “codes”. If the computer has issued a code pertaining to the O2 sensor, the sensor and it’s wiring should be tested. Usually when the sensor is bad, the engine will show some loss of power, and will not seem to respond quickly.
What will damage my O2 sensor?
Home or professional auto repairs that have used silicone gasket sealer that is not specifically labeled “Oxygen sensor safe”, “Sensor safe”, or something similar, if used in an area that is connected to the crankcase. This includes valve covers, oil pan, or nearly any other gasket or seal that controls engine oil. Leaded fuel will ruin the O2 sensor in a short time. If a car is running rich over a long period, the sensor may become plugged up or even destroyed. Just shorting out the sensor output wire will not usually hurt the sensor. This simply grounds the output voltage to zero. Once the wiring is repaired, the circuit operates normally. Undercoating, antifreeze or oil on the *outside* surface of the sensor can kill it. See how does an Oxygen sensor work.
Will testing the O2 sensor hurt it?
Almost always, the answer is no. You must be careful to not *apply* voltage to the sensor, but measuring it’s output voltage is not harmful. As noted by other posters, a cheap voltmeter will not be accurate, but will cause no damage. This is *not* true if you try to measure the resistance of the sensor. Resistance measurements send voltage into a circuit and check the amount returning.
How does an O2 sensor work?
An Oxygen sensor is a chemical generator. It is constantly making a comparison between the Oxygen inside the exhaust manifold and air outside the engine. If this comparison shows little or no Oxygen in the exhaust manifold, a voltage is generated. The output of the sensor is usually between 0 and 1.1 volts. All spark combustion engines need the proper air fuel ratio to operate correctly. For gasoline this is 14.7 parts of air to one part of fuel. When the engine has more fuel than needed, all available Oxygen is consumed in the cylinder and gasses leaving through the exhaust contain almost no Oxygen. This sends out a voltage greater than 0.45 volts. If the engine is running lean, all fuel is burned, and the extra Oxygen leaves the cylinder and flows into the exhaust. In this case, the sensor voltage goes lower than 0.45 volts. Usually the output range seen seen is 0.2 to 0.7 volts. The sensor does not begin to generate it’s full output until it reaches about 600 degrees F. Prior to this time the sensor is not conductive. It is as if the circuit between the sensor and computer is not complete. The mid point is about 0.45 volts. This is neither rich nor lean. A fully warm O2 sensor *will not spend any time at 0.45 volts*. In many cars, the computer sends out a bias voltage of 0.45 through the O2 sensor wire. If the sensor is not warm, or if the circuit is not complete, the computer picks up a steady 0.45 volts. Since the computer knows this is an “illegal” value, it judges the sensor to not be ready. It remains in open loop operation, and uses all sensors except the O2 to determine fuel delivery. Any time an engine is operated in open loop, it runs somewhat rich and makes more exhaust emissions. This translates into lost power, poor fuel economy and air pollution. The O2 sensor is constantly in a state of transition between high and low voltage. Manfucturers call this crossing of the 0.45 volt mark O2 cross counts. The higher the number of O2 cross counts, the better the sensor and other parts of the computer control system are working. It is important to remember that the O2 sensor is comparing the amount of Oxygen inside and outside the engine. If the outside of the sensor should become blocked, or coated with oil, sound insulation, undercoating or antifreeze, (among other things), this comparison is not possible.
How can I test my O2 sensor?
They can be tested both in the car and out. If you have a high impedence volt meter, the procedure is fairly simple. It will help you to have some background on the way the sensor does it’s job. Read how does an O2 sensor work first.
Testing O2 sensors that are installed
The engine must first be fully warm. If you have a defective thermostat, this test may not be possible due to a minimum temperature required for closed loop operation. Attach the positive lead of a high impedence DC voltmeter to the Oxygen sensor output wire. This wire should remain attached to the computer. You will have to back probe the connection or use a jumper wire to get access. The negative lead should be attached to a good clean ground on the engine block or accessory bracket. Cheap voltmeters will not give accurate results because they load down the circuit and absorb the voltage that they are attempting to measure. A acceptable value is 1,000,000 ohms/volt or more on the DC voltage. Most (if not all) digital voltmeters meet this need. Few (if any) non-powered analog (needle style) voltmeters do. Check the specs for your meter to find out. Set your meter to look for 1 volt DC. Many late model cars use a heated O2 sensor. These have either two or three wires instead of one. Heated sensors will have 12 volts on one lead, ground on the other, and the sensor signal on the third. If you have two or three wires, use a 15 or higher volt scale on the meter until you know which is the sensor output wire. When you turn the key on, do not start the engine. You should see a change in voltage on the meter in most late model cars. If not, check your connections. Next, check your leads to make sure you won’t wrap up any wires in the belts, etc. then start the engine. You should run the engine above 2000 rpm for two minutes to warm the O2 sensor and try to get into closed loop. Closed loop operation is indicated by the sensor showing several cross counts per second. It may help to rev the engine between idle and about 3000 rpm several times. The computer recognizes the sensor as hot and active once there are several cross counts. You are looking for voltage to go above and below 0.45 volts. If you see less than 0.2 and more than 0.7 volts and the value changes rapidly, you are through, your sensor is good. If not, is it steady high (> 0.45) near 0.45 or steady low (< 0.45). If the voltage is near the middle, you may not be hot yet. Run the engine above 2000 rpm again. If the reading is steady low, add richness by partially closing the choke or adding some propane through the air intake. Be very careful if you work with any extra gasoline, you can easily be burned or have an explosion. If the voltage now rises above 0.7 to 0.9, and you can change it at will by changing the extra fuel, the O2 sensor is usually good. If the voltage is steady high, create a vacuum leak. Try pulling the PCV valve out of it’s hose and letting air enter. You can also use the power brake vacuum supply hose. If this drives the voltage to 0.2 to 0.3 or less and you can control it at will by opening and closing the vacuum leak, the sensor is usually good. If you are not able to make a change either way, stop the engine, unhook the sensor wire from the computer harness, and reattach your voltmeter to the sensor output wire. Repeat the rich and lean steps. If you can’t get the sensor voltage to change, and you have a good sensor and ground connection, try heating it once more. Repeat the rich and lean steps. If still no voltage or fixed voltage, you have a bad sensor. If you are not getting a voltage and the car has been running rich lately, the sensor may be carbon fouled. It is sometimes possible to clean a sensor in the car. Do this by unplugging the sensor harness, warming up the engine, and creating a lean condition at about 2000 rpm for 1 or 2 minutes. Create a big enough vacuum leak so that the engine begins to slow down. The extra heat will clean it off if possible. If not, it was dead anyway, no loss. In either case, fix the cause of the rich mixture and retest. If you don’t, the new sensor will fail.
Testing O2 sensors on the workbench.
Use a high impedence DC voltmeter as above. Clamp the sensor in a vice, or use a plier 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 lead 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 carbureted 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. There is almost always *no* benefit in replacing an oxygen sensor that will pass the test in the first line of this paragraph.
Rick Kirchhof Austin, Texas | Experience is what you
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1. Find a sweet song that you like.
2. Drag and drop the song into iTunes.
3. If the song is too long for your taste, right-click Get Info and go to the Options tab. Adjust the start time and stop time to get to a length that you would like. Many phones don’t have a lot of space, and this may be an issue.
4. Press OK and then go to the preferences pane. (Command-,)
5. In the advanced pane, then the importing tab, make sure that your settings are turned to Import Using MP3 Encoder.
6. Press OK
7. Right click on the song and click Convert Selection to MP3. This will create a new file at the length that you choose.
8. Drag this file to the desktop.
9. If you have your phone already set up for bluetooth connectivity, all you need to do is with the file clicked press (command-shift-b). This will pull up the send file box, and you pick which device to send the file to.
The most common problem with Sammis is the choke setting…other things like timing can affect it but i’m sure you’ve already checked all of that… anyway what you do now is get a long flat head screwdriver and lay it on top of the same mount that your accelerator cable runs through before it gets to that large cam on the bottom of the carb that we talked about before…it is the same bracket or mount that the two 12 mm nuts are found that hold the cable adjustment… anyway that bracket is going to bend down a bit after you use it for the leverage you’ll need to do the adjustment on this mark you need to make but don’t worry about the bending because you can just bend it back up into place after you are done….you’ll see what i mean after you do the adjustment…anyway, lay the handle of the flat head on the top of the bracket and then with the flat head of the screwdriver catch the end of the small cam that is pointed your way and push down on the handle of the screwdriver which will cause the bottom lobe of that cam to go up!!!!…so far so good???…now take a small nail or drill bit that will fit snugly into the hole that is in that same cam and you’ll see that there is also a hole in the bracket above this small cam that when the lobe is pushed up flush with you can run the drill bit or nail all the way through both and whalah!!! The cam will stay in place now without your having to hold the screwdriver any more!!!…now what you need to do is use that same long flathead to slowly put pressure on the “l” or “c” shaped finger on the other end of this same small cam that we have been dealing with all this time… if you take a look at it you’ll see how it is actuated by the thermocouple that comes down from the other housing above it…that thermocouple is actuated by water temperature from the two hoses that run into that same housing…anyway in order to get the idle down, you need to use the screwdriver tip to push that finger up…. do this process slowly and as you bend it a little at a time you’ll see that the mark on the small cam will eventually line up with the rod we talked about before… that is where you need for it to be to operate correctly…remember that you need to bend a little…i’d say not more than 1/16th of an inch at a time; then remove the drill bit and see where you are and then repeat these small adjustments until the marks come into alignment…after that straighten the bracket back up that you bent and start your engine!!! You should be much happier.
Now and again, Apple’s technical specifications state a maximum amount of RAM that’s not actually correct. It was the case with the iMac G4, and believe it or not, it’s the case with some MacBooks and MacBook Pros. Any 2.2GHz or faster MacBook Pro (except the 2.33GHz models), and any MacBook made in November 2007 or sooner, actually supports 6GB of RAM, not 4GB! Like all our RAM, the 4GB PC5300 chips carry a lifetime warranty and are guaranteed Mac-compatible.
You can tell the speed of your Mac by selecting About This Macfrom the Apple menu on the upper-left corner of your screen. If your MacBook Pro is at 2.2GHz or faster, it will accommodate the upgrade, but it’s a bit tougher to tell if your MacBook qualifies. Your MacBook’s serial number is the best way to know for sure whether it can hold 6GB.
Your serial number is very deliberately constructed. The first two characters tell you where the machine was manufactured, the third tells you the year in which it was manufactured, and the fourth and fifth characters tell you the week it was made. Let’s take a hypothetical serial number and dissect it—say, W88231FMYK0. W8 indicates that the machine was made in the Shanghai, China facility. The second 8 indicates the year of manufacture (2008). And the fourth and fifth characters show the week it was made. So, we know from this serial number that the MacBook was made in Shanghai in the 23rd week of 2008.
How does this relate to RAM in your MacBook? Well, MacBooks manufactured in the 48th week or later in 2007 qualify for the 6GB RAM upgrade. When you look at your serial number, you can ignore the first two characters, as it really doesn’t matter where your machine was made. But make sure the third character is 7 followed by 48 or higher. Any MacBook made in 2008 qualifies for the upgrade.
I know your next question already: What about requiring matched pairs of RAM for fastest performance? Well, I’ve never really believed that the average user can tell a difference between a machine with matched pairs and one without. There are several studies out there confirming that the infinitesimal speed loss from not interleaving is more than offset by the availability of more physical memory. Any time you can avoid the use of virtual memory, you’re going to see a big speed boost.