I have a 90 RS 4 door as some of u may know and that means that its a non-OBD. So luckily I get to buy the 40ish dollard O2 sensors from the parts store. Well the other day I was having overheating problems. I fixed that, didn’t realize that the radiator cap has such a strong influence on the temp of the car! Anyways so I reset my ECU cuz I adjusted my timing and then I was reading a post about if you unplug the O2 sensor my check engine light should of came on. Well I did unplug the O2 sensor and the car seemed to have absolutely NO effect at all when I did so, but the check engine light didn’t light up. I changed my sensor to a Bosch kind from Kragen because my older one wasn’t letting me pass smog. So does this mean that my Bosch sensor is not working? Or do I need to get a new one maybe? What gives? How can you test your O2 sensor to see if its working or not? And maybe I didn’t have the light come on because of the non-OBD status? The sensor is a one wire kind. Any ideas any1?
I have a 90 LS. The check engine light should come on with no o2 sensor installed. It will seem to run okay but I think you will burn tons of fuel without an o2 sensor. That’s the only thing I can think of now. How’s your fuel economy? I get about 310 miles per tank average.
Ben
how long did you leave the car running with no o2 sensor hooked up.My engine light would come on before and i checked the computer for codes and it was the o2 sensor, however if i started my car and didn’t drive my light wouldn’t come on, when i would drive off after a few minutes it would come on, so if you just started the car and it sat there the light may not come on yet.If you replaced the o2 sensor and theres no light you should be fine, you can always check the computer for codes but from what you are saying i think you’re fine.hope this helps
if you want to check your 02 . you could use an voltmeter just take a pin and slide it in the connector next to the wire and after your car is at running temp it should fluctuate betwwen 100-900 mv.
yes drive around for a litte bit then it should come on…not sure why… but thats what mine did when it wasn’t pluged in…good luck…
later,
Dan 
Well I adjusted my valves and prior to adjusting them I would get about 300-340 miles per tank, after adjusting I’m getting crappy mileage. I have to fill up around 250-270 miles per tank. I wanted to adjust the timing because this could b the reason for crap gas mileage, and resetted the ECU since I did the valve adjustment. I will go and test out the O2 later today and see what happens.
Say if it doesn’t turn on, what could b the problem? That means that that wire is getting power from somewhere to the ECU. I haven’t checked the codes on the car in like years, never really had a reason to.
I am running rich I suppose at hard acceleration due to the black smoke coming out when WOT.
Shanks