Oxygen Sensor Voltage Readings
 

I realize that a great many of folks here already have their Oxygen Sensor disconnected so no bashing please... Since I have owned my car (Sept 2003) I have never been able to get any reading from the Oxygen Sensor (my fuel mileage is rather poor at 17.70 highway driving). My understanding is that when the car is running and up the normal operating temperature, the sensor generates a voltage and ideally this should be around 0.45V. I have replaced the Oxygen Sensor and it still measures no voltage. I currently have the factory heat exchangers/cat/muffler system in the car. I performed a test by removing the Oxygen Sensor and applying heat via a hand held propane torch while measuring the voltage on the sensor and I was able to repeatedly obtain readings that appeared to be correct (up to 1.00V). Since the car is a 1981 model there is only one sensor lead and a lot of heat must be generated in order to produce this signal voltage. Is is possible that my car is running so rich that the the exhaust temperature is unable to reach the proper level thus not produce a voltage through the Oxygen Sensor?

Here are the Bosch specs and related <FONT FACE="SYMBOL">l</FONT>'s

http://forums.pelicanparts.com/uploa...1081027643.jpg

O2 sensors are useless at idle bring the car up to 2500 RPM and see if you get a reading.

Having never had one of the new fangled Motronics cars that need those things, what happens to the DME when the signal from the 02 sensor fails or is not present? Does it switch to a default rich mode?

TT

Yes
The Lambda oxygen sensor must be operational before the Lambda closed-loop control circuit can function. An auxiliary evaluation circuit monitors this factor on a continuing basis. A cold oxygen sensor or damaged circuitry (short or open circuits) will generate implausible voltage signals which are rejected by the
ECU. The heated Lambda sensors used in most systems are ready for operation after only 30 seconds. Cold engines require a richer mixture (<FONT FACE="SYMBOL">l</FONT> < 1) to idle smoothly. For this reason the Lambda closed-loop control circuit can only be activated once a set temperature threshold has been passed. Once the lambda control is activated, the ECU uses a comparator to convert the signal from the sensor into a binary signal. The controller reacts to the transmitted signal (<FONT FACE="SYMBOL">l</FONT>> 1 = mixture too lean, or <FONT FACE="SYMBOL">l</FONT> < 1 = mixture too rich), by modifying the control variables (with an initial jump followed by a ramp progression). The injection time is adjusted (lengthened or shortened), and the control factor reacts to the continuing data transfer by settling into a constant oscillation (Figure 7). The duration of the oscillation periods is determined by the flow times of the gas, while the "ramp climb" maintains largely constant amplitudes within the load
http://forums.pelicanparts.com/uploa...1081095913.jpg http://forums.pelicanparts.com/uploa...1081095923.jpg

I have performed yet another test this morning: spliced into the single wire coming fron the Oxygen Sensor and ran a length of wire from this splice, outside the car, through the passenger window, and into my 'cockpit' where I connected the wire to a multimeter using an alligator clip. I used the computer ground underneath the passenger seat as a ground for this test. After properly connecting these leads I place the multimeter in the passenger seat and set the unit for Volts (DC) and go for a test drive. After allowing sufficient warm up time I turn the multimeter on and I still get 0.000 Volts (peak RPM was 4,200). After parking the car I also tried connecting my ground to the catalytic converter just to ensure that I had a proper ground and maintaing 3,000 RPM's I still see no voltage. I am at a loss on why I see no voltage after verifying the Oxygen Sensor is indeed functional - see original post. The meter is new and has been tested. Does anyone have any thoughts???
:confused:

I've heard that lambda needs very high impedance input circuitry and is easily damaged by running voltage trought it.

Maybe you should measure right off the sensor. Your wire to the ECU may be toast.

The Lambda unit doesn't default to a rich mixture without the O2 hooked-up.
The actual mixture goes to a value determined by the control pressure - WUR,
system pressure, and Lambda unit open loop duty cycle (50%), i.e a neutral
value.

If the O2 lead is not shorted to ground or open, your meter is on D.C.
volts, and the O2 is O.K. & at the needed temp, then the engine is
running very lean, < .45 lean, >.45 rich, <<.45 very lean; e.g. a bad
Lambda unit or too high a control pressure.

This is assuming that your mixture is set at 0.4 to 0.8% CO ** 80 to 83 Models USA and Canada.

**Measured in front of the catalytic converter with oxygen sensor pulled off.

Porsche Technical Specifications

a neutral value - that which was set by the mixture screw on the fuel distributor
and by the control & system pressures