I have a 96 Ford ranger with a 2.3 and manual transmission. I decided that it was probably a good time to changer out the o2 sensors. Originally it had 2. One before and one after the cat. But the owner before me cut the cat off. I didn't realize until now that there is only one sensor. Not sure if this is okay or not. But what I want to know is, which sensor to replace it with. Do I replace it with an upstream sensor or a downstream. Thanks

 

They should be the same part number, but upstream is the one you want, the one closer to the engine and the one that helps computer to keep engine running with correct air/fuel mix, they last about 100k miles, MPG goes down as they wear out, not major drop just less and less over time, so they pay for themselves over the next 100k miles.

Downstream(after Cat) O2 sensor is used to test if Cat is working, so for emission system not engine system, although it can play a small part in overall long term fuel trims.


You should have a CEL(check engine light) on if that downstream O2 sensor is missing, because it is part of the emissions system.

 

Thanks RonD I replace the one with an upstream and it definitely changed the way it runs. I do have a check engine light for the one that is cut.. I hate having check engine lights. Is there any way I can remove the code for a missing o2 without installing one?
Thanks

 

No, not really anyway to trick that type of monitor, O2 sensors generate there own voltage, so it isn't as simple as putting a jumper on the wiring.
There is also a Heater circuit on each O2 sensor that is monitored.

You probably could do it with custom circuit board but just putting on a Cat and O2 sensor would be less trouble and probably less money if you have to have someone else build the circuit board.