Here are some photos of O2 sensor I'm checking out. I had a hard time finding it from manuals - were either wrong or diagrams hard to understand. Maybe this will help someone else.

Other sensors are OK - anyone know what each of the other 3 are?

1990 Mitsubishi Eclipse 2.0 DOHC Non-Turbo

Location of O2 sensor and connector
http://imageshack.us/photo/my-images/822/o2sens01.jpg

Sensor on inlet of thermostat
http://imageshack.us/photo/my-images/715/sensor1n.jpg

2 sensors below thermostat
http://imageshack.us/f/214/sensor23.jpg