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Old 05-07-2008, 12:09 PM   #11 (permalink)
Coyote X
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Location: Southen West Virginia
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Metro XFi - '93 Geo Metro XFi Convertible
90 day: 62.17 mpg (US)

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A 4 wire sensor is better than a 1 wire. I had a voltmeter hooked to my o2 sensor in my car and when it had a 1 wire anytime I did eoc, coasted in gear, or let it idle for about 30 seconds the sensor cooled off and took about 30 seconds to start reading again once I started driving unless I held it to the floor to heat it faster. With the 4 wire sensor it started working within 30 seconds of starting the car and stayed working while eoc or whatever.

The O2 goes high impedance when it isn't working so the computer knows to ignore it and just run off the fuel tables so without a voltmeter it is hard to tell when a sensor is working or when it is cold. It is easy to convert a 1 wire car to a 4 wire. And all 4 wire sensors are the same so go to a junkyard with a propane torch and voltmeter and get a few of them really cheap.

Here is a writeup I have on my site detailing O2 sensors:
The factory one wire Oxygen sensor works well for what it was designed for but it does have limitations. 4 wire sensors have been used for a while so it is easy to find them at junkyards. It is easy to test a sensor to make sure it is working with just a voltmeter and propane torch. Take the sensor you want to use out of the car and hook your voltmeter up to the sensor wire and sensor ground wire using the chart on this page to figure out the wires. Once you have it hooked up you should be reading 0 volts. light the propane torch and hold the tip of the inner blue cone on the oxygen sensor. It takes a few seconds to get it up to temperature and you should see the voltmeter go to .9-1.4 volts. Once you get it there twist it around to make sure the whole element is heated evenly and any buildup on it is burned off. The voltage should drop within 1-2 seconds to under .1 volts when you take the propane torch away. If it does not go down quickly then try turning the propane up higher and burn off any deposits on the sensor you can. It will not hurt the sensor to make the case glow orange. After a few minutes of cleaning the sensor it should respond quickly to the torch being pulled away from it. If it is slow to respond to the torch being added or taken away then it is probably lead or silicon fouled and you can give up on it and go to the next one. If after 5 minutes it isnít working like it should then give up on it and pull another one off a different car in the junkyard. I would grab an extra one while I am at the yard just to have a spare they are cheap.

Type 1 Type 2 Type 3 Description
Black White Black Heater Circuit
Black White Red Heater Circuit
White Grey Black Sensor Ground
Blue Black White Sensor Output

The Wiring is normally one of these colors. Make sure you only pick colors from one column. Things are much easier if you cut as much of the harness out of the junk car as you can to give you as much lead wire as possible. If not at least get the connector and a few inches of wire to splice into your existing harness. The connections should be pretty easy. The sensor ground should run by itself to a chassis ground and not just grounded to the engine in case the engine has a bad ground. The sensor output goes to the factory Oxygen sensor wire. The heater wires do not have a polarity so one wire should go to ground but not using the same wire as the sensor ground. The other wire should go to the ignition and only have power when the key is in the on position and not when the key is on accessory.

The advantage wit the new sensor is that the computer knows when the sensor is working and will use it to adjust the A/F ratio. The old sensor would cool off at idle and while coasting and take a few seconds to get back up to temperature. This left times when the computer could not adjust the A/F ratio. The new sensor has a heater so it will stay working at idle and as soon as you give it gas from coasting. It also heats up much quicker so it starts working much sooner when starting the car. The most obvious thing you will notice the idle is smoother and it doesnít hesitate as much when going from coasting to accelerating. Overall this is a very simple and cheap mod so if you have some free time I would do it if your car has a 1 or 3 wire sensor in it now.


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