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O2 sensor testing
How would I know if I need to replace my O2 sensor on my 82 SC?
I don't feel any buzzing on the frequency valve when the car is running. Thanks |
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03-25-2023, 10:49 AM
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Do you mean an air bypass valve. o2 sensor would be on the exhaust. bypass valve would be between throttle body and intake.
If it is the o2 sensor you can measure the volatage at the plug. Mine stopped giving voltage when hot so had to get a new one. |
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03-25-2023, 12:47 PM
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The O2 sensor, the Bentley service manual says to test with the plug connected with the test lead connected. How would I insert a lead in there?
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03-25-2023, 01:20 PM
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Join Date: Mar 2019
Posts: 1,600
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Rig up some kind of "tee" connector and measure with a DVOM (or if you're careful, sneak the probe under the rubber boot until it contacts the terminal). Voltage should vary from about 200mV to 800mV, with a bias voltage of about 450mV with the key on and engine not running. If it's stuck on the low end, it could be a bad sensor or that the engine really is lean. If it's stuck high, the engine is too rich. Seldom do O2 sensors fail outputting high voltage.
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03-26-2023, 06:44 AM
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I created a wire lead with a red male plug to a wire that I use. What kind of end does your sensor have. I have the big female end one so even a multimeter will fit in it.
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03-26-2023, 01:56 PM
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It's the plug on the driver side engine bay, the one that usually snaps off.
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03-26-2023, 03:01 PM
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Join Date: May 2004
Location: Boulder, Colorado
Posts: 7,275
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Joe - the frequency valve should "buzz" whether the O2 sensor is working or not. If it isn't buzzing, either it isn't connected (done recent work back there here the wires connect to the FV?), or it has failed (which I think is unusual), or somehow the 12 pin connector for the CIS in the front left of the engine compartment has been disconnected or otherwise the control wire has been compromised, or the mini brain in the silver box under the passenger seat itself isn't working. There is a relay near the center tunnel which delivers power to the brain, which should switch on when you start the car. It gets its power from the same fuse that protects the interior lights!
The engine will start (but not easily), and run (better than one might think) without any of this working, but troubleshooting this will make you much happier when you straighten things out. I'm a bit dubious of using just your ear to make sure the FV is working. Better to put your hand back there in it to feel its vibrations. And to validate your belief that it isn't working. What operating issues do you have which led you to start in on this? The 3 pin black rubber shrouded connector can be used to measure (usually indirectly) the pulse width modulation value which controls the FV. If you get a reading from it, the FV is getting input. In the absence of a signal from the O2 sensor, the FV system defaults to a 50% pulse width. However, that 50% can occur under several engine operating conditions, so would be tricky to sniff out a failed sensor from that data. As noted, you can check the O2 sensor directly for voltage to see if it is working. |
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03-26-2023, 09:03 PM
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If I wanted to see if the plug is getting power to the FV would I need to bypass the fuel pump relay and turn the ignition to the run position, I did that and I'm not getting power to the plug using a test noide. All the interior lights are working as well as the front trunk light.
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03-27-2023, 08:35 AM
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