On my old engine I thought I remember the O2's reading around a constant 450v at closed loop on my scanmaster.

Mine now under the same conditions are reading different. The left at around 350V and the righ is bouncing and the BLM's are acting strange.

Does this behavior at closed loop cold engine sound normal?

 

i dont think they are supposed to be constant. the right is probably good and the constant bad.

 

That being said I am lost why the two are much different at start up from one motor to another. I thought the O2's did not do jack in closed loop?

 

The PCM ignores the O2 sensors in open loop. A cold O2 sensor will read 450mV; as heat from the exhaust start to warm up the O2 sensor the mV readings will start to bounce above and below 450mV. Even though these readings are moving, the PCM will ignore them until closed loop is reached.

 

So if at cold startup if one is 350 and the other one is already bouncing then they are bad right?

 

swap sides and see if the constant reading follows the sensor.

Dan

 

The o2 sensors are suppost to jump back and forth pretty much between .2 and .8 volts. If it constantly keeps going lower it means it is reading a bit lean, and if higher rich. But if one is just staying at the same # no matter what then yea I beleive that o2 would probly be bad.

 

My engine is missing due to arcing plug wires, does this cause the BLM to jump up?

 

Yes, unused oxygen passing out of the cylinder and across the O2 sensor will be interpreted as a false lean condition. It is "corrected" by increasing the BLM.