Im testing the Oxygen sensor on my '80 245 today, and I've read the books so many times I've confused myself.

I get the car up to temperature (drove it around for a while), hook up the voltmeter (+) to sensor with it connected, and neg. to ground - it fluctuates around .5 volts fine....

Then I turn car off, disconnect sensor and connect voltmeter (+) to sensor, neg to ground. Start car and I get no voltage at idle (well maybe .002 volts or less).

If I raise the RPM's the voltage does increase, as high as .86 volts or so. But, doesnt the book say there should be a greater fluctuating voltage at idle?

Other minor details: the car "bucks" horrendously and I havent been able to keep the frequency valve duty cycle at a consistant level. (there may be several things going on here)


thanks for any response!
NOAH

When you unplug the sensor from ths system the "computer- Lamda module" will switch to open loop mode and usually will not fluctuate. If you hook up a Digital Volt Meter when the O2 sensor is plugged in it should fluctuate around .5 volts. It's hard to see with a DVM. I have one that also has a bar display which is easier.
Also when you first start the car the sensor may be to cold to have an output.

There is a way to test with the O2 sensor unplugged.
This also checks the Lamda module.
Connect the meter to the O2 sensor.
Start the engine.
Ground the other lead which is the input to the Lamda control.
The O2 sensor should approch 1 volt when it is warm.

then hook the positive side of a 1.5 volt battery to the input of the Lamda module and the negetive of the battery to ground.
The O2 sensor should approch 0 Volts.

Gary

hi there, with the car running the o2 sensor unplugged and hookeed to your meter it should fluctuate also around .5 but changing rapidly, maybe your 02 sensor is lazy (going bad) as i understand it. i installed a new 02 sensor and the reading is constantly changing very quickly. the 02 sensor is important for your application. im just learning, but just trying to help. the bentleys manual is very informative on this subject.