4 Wire Oxygen Sensor

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 isn’t 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 doesn’t 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.

9 Comments

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  1. Hi Rick
    I’m new at this. I do have a near by
    u-pull yard. What autos should I be looking for to find this 4 wire injector?
    How far back did they start using these?
    Thanks again
    Doug (new owner of a 92 XFI)

  2. Any 96 up car should probably have a 4 wire oxygen sensor. Take a propane tank and a voltmeter like described in the article to find a good one or 2.

  3. so the heater circuit remains on the whole time that the car is on?? did you try just this mod and run a couple tanks of gas to see if there was an improvement in mileage?? thanks.

  4. i did this mod on my 91 lsi 4/auto. after my first full tank, mpg dropped from 38.5 to 37.6. i guess i can’t blame the 4 wire sensor, for this drop, so i will keep it on there and see what happens. my only other mods is an xfi cam, along with block heater and wair air intake. its winter time here in the south usa, so i’m sure mpg will pick up when warm weather comes back. btw, if anybody is wondering, i hooked up the heater circuit to 12v & ground to see how hot the sensor gets while on a workbench. the highest temp i recorded w/non contact thermometer was almost 300 f. this was after about an hour of being plugged up. hope this helps.

  5. The heater is supposed to stay on when the ignition is in the on position. It doesn’t take that much power to run the heater circuit in the sensor. The mileage increase from this mod alone won’t be a lot and will depend on your driving conditions. If you do engine off coasting and turn the engine off at stoplights the 1 wire cools quickly and takes a bit before it is working again. The 4 wire will keep working the whole time. So under worse case conditions this might get you another 3-5mpg but normal easy driving it might only be worth 1mpg. It is a cheap mod and pretty easy so I say it is worth doing.

    The drop in mileage is probably your warm air intake. These engines are very well tuned and hot air going into the intake no matter how I try and do it has always killed my mileage. Cold air intakes have not shown any change to mileage one way or the other though, but they did give a bit of top end power if that matters to you. I have tried air from 150 degrees right off the exhaust manifold to 10 degrees above ambient air temperature and pretty much anything over 90-100F makes the mileage go down.

  6. Which Brand O2 Senssors are Inexpensive?

    The Stock Geo #2 O2 Sensor
    Costs more than $100.

    ARe Chevy or Ford O2 sensors Reliable and inexpensive?

  7. Thanks for the info! This was what i needed to know

  8. ANY 4 wire sensor will work? I have an 88 Cherokee where I accidentally ordered the wrong O2 sensor for it. the sensor “appeared” identical but the plug was reversed (it was for the 4cyl Cherokee) so I swapped the plugs and it did NOT run properly.

    I eventually gave in and ordered the right O2 sensor and the problems went away almost instantly.

    So how do I know which will work? are some different? maybe I just wired it wrong or something when I swapped the plugs??

    Just curious anything I can do to make it better is appreciated! (I will have my 94 XFI in 3 more weeks 🙂

  9. Did this 2 my 96 metro. Was ready half a volt cold and the same hot. Used my A and O on the weakest flame I could make and got the tip just cooking. Works like bran new now. Mine was the type 1 o2 sensor

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