Is the .9 volts supply voltage, or is that what the PCM is seeing as the return? Supply should be 5 volts. Return should vary between zero and one. A digital meter doesn't react fast enough though, the scanner should display accurate data though, provided it samples often enough.

 

it varies between .8 and 1, so I called it .9, but doesn't that mean its really rich??

 

Yup. Or, the sensor is simply lying...... Ideally, it should bounce between values greater, and less than.. .45 volts. If it stays higher, its running rich, lower, lean. How old is the sensor??

Is the PCM going into closed loop?

 

I didn't replace it with everything else. Honestly I think its five years old, I know I changed it before I got my Cat.

I don't know how to check for the closed loop.

 

Doesn't your scanner tell you?