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O2 readings Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 11 Sep 2002 11:46:28
In Reply to: Thanks Ari, Quasi, Tue, 10 Sep 2002 22:20:33 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Ideally the O2 sensor will be swinging between around 0.2 and 0.8 volts, crossing 0.5 about once per second. Because digital voltmeters have a relatively slow update rate, you'll see some variation on that.
O2 sensors are designed so that 0.5 volts is the ideal stochiometric ratio. (OK, just showing off). But to make 3-way catalytic converters work, the engine control swings the mixture very slightly around that ratio, and that's why the O2 sensor voltage varies. The O2 sensor works by comparing how much oxygen is at the tip as compared to the amount at the back of the sensor where the wires come out - normal atmosphere. Big difference, bigger voltage. No difference, no voltage. 0.2 volts is a lean mixture - lots of extra oxygen. 0.8 or 0.9 volts is a rich mixture - no extra oxygen.
The sensor is pretty sensitive, so 0.2 or 0.9 volts is not a big mixture change. The sensor saturates at around 0.0 to 0.2 volts at the lean end, 0.9 or so at the rich end. So 0.9 can be slightly rich or incredibly rich. If you see the O2 sensor output varying anything at all between 0.2 and 0.9, then you know the engine is running right around the proper mixture.
In your case, I'd be looking for the sensor stuck at either 0.2 or 0.8/0.9 volts. (voltages vary from sensor to sensor, and where you're finding your ground point). If the sensor is stuck at 0.2, then it's telling the ECU that the mixture is lean, and the ECU will respond by pumping in more fuel. To me, that would indicate an O2 sensor problem. However if the O2 sensor is stuck at 0.9 volts, then it's telling you the mixture is rich, which would agree with observations (poor gas mileage). That would imply a good O2 sensor, and something else driving your rich.
Ari
posted by 192.249.4...
, Tue, 10 Sep 2002 18:21:53, Wed, 11 Sep 2002 11:46:28 <-- Viewing This Message
, Wed, 11 Sep 2002 13:17:17
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