How do I check the O2 sensor on a '89 I6 300? shes running kind of rough. like its not gettin gas but i know it is. I thought id start at something small like a sensor that hasnt had attention for a while. Thanks.

 

You can't really check the O2 sensor, but if it's been over 50,000 miles since it was changed, that's probably a good idea anyways.

 

she has over 192,000 miles on the odometer. I know the previous owner real good. Ill ask him when it was last changed.

 

He says hes never replaced it himself. But he also said hes had it in the garage a couple of times. Either way,i took it off and sprayed carb and choke cleaner through it reall good. then blew it all out. but it back on and waiting to see if it works. The local parts house wants $41-45.00 for one new.

 

You might want to invest in a new o2 sensor at that mileage, even with the high price. My Haynes says the only way to clean them is to torch them and burn the garbage off them, if its there. The o2 sensor is one of the main sensors for the computer, and it's important for it to work properly. Not sure if choke and carb cleaner is good for it either, you might try some injector cleaner if it's running rough, and change the fuel filter, they get clogged up and stop the gas flow, and are only 5 bucks.

Good Luck.

 

Yes, you can check your O2 sensor.

First, check your computer codes. 2-digit codes indicating problems: 41, 42, 91, 92. 3-digit: 136, 137, 139, 144, 171-178.

Second, check the sensor output voltage. On my 88 4.9, there was a connector between the downpipe and the sensor, and another right near the battery. Mine was a 3-wire; one wire for the heater, one ground, one for the signal. 4-wires have an additional green (?) wire to give the sensor it's own ground. Signal wire was white. With the engine HOT and running, pull the connector by the battery (you really shouldn't stick your hand between the oilpan and downpipe on a running engine ;-), and with a good <b>digital</b> multimeter (cheap analogs will current-drain the voltage towards zero), check the voltage between the white wire and battery ground. It should be rapidly switching between about .2V and .6V. Stochiometric is .45, but the sensor is extremely non-linear. .2 is just barely lean, .1 is way lean, etc., same for rich. The faster the switching, the better. If it reads constant anything, clean it or junk it. For the trouble of removing the thing, you might as well replace it. Modern sensors are much better than older sensors, etc., plus you get a guaranteed 50k mi. out of the thing. Be sure to reset the computer after you change the sensor. Computer will need to recalibrate itself to the new sensor, and to clear any codes.

Here's a nice thread about removing the O2 sensor on my 88 4.9; applicable to any other vehicle. <a href="https://www.ford-trucks.com/forums/showthread.php?p=1876206">https://www.ford-trucks.com/forums/showthread.php?p=1876206</a>

Check your plugs as well. A failed O2 sensor will put the computer into open-loop, and the resulting richness/leanness depends on the condition of the rest of your sensors. My truck ran way lean. Decent mileage, no torque, knocked like crazy, and it roasted 5/6 plugs.

$40 isn't bad for an O2, and that's Bosch at Advance. Recommend getting a $12 haynes manual while you're there.