o2 readings

[1kwick6]

How can you tell you have a bad oxygen sensor

[gofstbuick]

O2 sensors work based on how fast it can respond to changes to the oxygen content in the exhaust (compared to atmospheric oxygen content). Two things of real concern is bias rich or lean and response time (in milliseconds). The test I use requires a digital storage oscilloscope (DSO), and a propane enrichment kit. Set your voltage to 200 millivolts(mv)/division and set your time scale to 200 milliseconds(ms)/division. Using a paperclip, push it between the O2 wire and the rubber insulation, so it contacts the O2 signal wire. Attach the positive lead of the DSO to the paperclip and the negative lead to a good ground source. If your scope requires a trigger voltage, set that to 600mv sloping down. When the O2 becomes active, you will see a high and low hills accross the screen. The slope lines should be smooth. If there is hash marks in the slope lines, this indicates a misfire. Because the DSO is seeing puffs of air from the misfire. For those that don't use a DSO to diagnose O2 sensors, this is an indication of how fast and precise a DSO is compares to a scanner. Your first test is to determine if the O2 is centered. Since we cannot force the O2 to constantly read 450mv, we will force the sensor to react at the extremes (lean and rich). If the sensor react properly at the extremes, then it is assumed to be centered. Begin flowing propane thru the air filter housing snorkel, and the sensor readings should flatline above 800mv, but not more than 1000mv. Shut the propane off and the readings should fall below 200mv, but not less than 0mv. Results out of spec on one or more readings indicates a ranging problem (replace O2 sensor). If ranging specs are okay, perform same test again, but after the propane is turned off, and the readings start to fall to almost the lowest reading, snap the throttle. This forced the computer into power enrichment mode and the O2 readings will rise rapidly. Measure form the lowest point just after the turn upward to just before the highest point (on the upward slope) just before the turn downwards. The response time should be less than 100ms. If your O2 cannot respond in less than 100ms, replace it. Because our engines are fuel injected, O2 response is critical to correct injector response.

[1badTTA]

After that reply on how to test an O2 sensor, I think I will just replace mine whenever I am in doubt. It certainly is nice to get the technical answer, but at 4:30 in the morning I am sure I wouldnt be able to do any of that test (even if I did have an O-scope) and would be better off just spendong the $30 on a new O2 sensor.

[Mile Hi GN]

Originally posted by 1badTTA
After that reply on how to test an O2 sensor, I think I will just replace mine whenever I am in doubt.

Thats the right conclusion.

They are cheap and easy to change - when in doubt, swap them out