ok 97 4.0 and my o2 sensor thats mounted in the cat is reading 1.000 all the time. does this mean that it is bad

 

Explain what you mean by that test measurement.

Proper testing of an oxygen sensor is a fairly complicated procedure.

 

i have a snapon obd2 scanner. that alows me to watch watch what the rpms are, and what the o2 sensors are doing and so on. the front o2 sensor fluxuates between .350 and .700 and the rear is allways 1.000. does this info help

 

Are you setting a code or do you have a check engine light for an oxygen sensor issue?

Curious as to why you are looking at this unless it is just incidental to your trying out the scan tool on your XJ.

The post-cat sensor is just there to measure efficiency of the catalytic converter, so unless it sets a check engine light, there isn't any pressing need to replace it.

You'd have to look up the sensor test procedure in the factory service manual to see if you can figure this out, but in general, oxygen sensor voltage should fluctuate rapidly between .4 and .6 volts, so this sensor after the catalytic converter may be out to lunch.

 

ok so needs to be replaced or not. and im not getting any codes at all. and aditional info just replaced the intake/exuast gasket is why i was watching the data

 

Don't replace it unless it sets a check engine light is what I would do. Won't affect engine performance any. If it gets bad enough, it will set a CEL.

 

ok thanks for the info