Rpm Reading & O2 Mv Readings

[mr.ricoe]

Just wondering if anyone had an idea were the rpm readings to the rpm gauge come from. The reason I asked is my rpm stop indicating but it still has 4bars illuminated and on my scanmaster the rpm's are able to read.

My other question is my o2 mv readings are always going up & down from 780 to 100 or varies. I just installed a heated o2 sensor. What are the readings suppose to be?

 

[mikestertwo]

Just wondering if anyone had an idea were the rpm readings to the rpm gauge come from. The reason I asked is my rpm stop indicating but it still has 4bars illuminated and on my scanmaster the rpm's are able to read.

My other question is my o2 mv readings are always going up & down from 780 to 100 or varies. I just installed a heated o2 sensor. What are the readings suppose to be?

The rpm reading comes off of the ignition module. There is a tach test connector located behind the alternator. If you have a steady 4 bars illuminated on the gauge then most likely the gauge died. Some people make the mistake of plugging the tach test connector into the fuel pump test connector which is also located behind the alternator and that will kill the tach reading but the tach will read "0" not 4 bars unless there is something wrong with the tach and it has an offset in it.
As far as your O2 readings, they look normal. They should cycle up and down.