?? on 02 Sensors....

[shadowracer]

OK here it is a heated O2 sensor will have 4 wires coming out of it two for the heater element and two to actual sniff your exhaust. A non heated O2 sensor will only have one wire coming out of it usually white in color. I've used bosch O2 sensors in the past in emergency situations and they have worked just fine. I purchased the universal kind that come with the connector and instructions really straight forward if you ask me.

Your 1990 Civic Si should only have one O2 sensor, your correct at that. Your car should have a non heated O2 sensor with a single wire coming out of it.

If you are going to change your O2 sensor yourself make sure you have a quality O2 sensor socket handy, along with some anti sieze, and a pair of mechanics gloves. Here is a lil advice being a 1990 your O2 sensor will probably give you hell trying to get it out unless you have a torch handy. As for me I don't have a torch handy so my trick is to let the car warm up to operating temp so that the exhaust is hot, hence the need for the Mechanics gloves. The heat from the exhaust will make the O2 sensor come out easier. I've done plenty this way and it works wonders. Hope this helps good luck