Mercedes-Benz Forum banner

1 - 5 of 5 Posts

·
Registered
1984 190E 2.3 8v
Joined
·
119 Posts
it is a sensor placed in the exhaust gas stream to signal the CIS to either enrich or lean depending on values.
 

·
Registered
1985 2.3 16v euro
Joined
·
35 Posts
sensor that either creates or changes voltage depending on oxygen content in the exhaust gases. some cars have them before and after the cat.
most have to be a minimum of 600 degrees to work, before that your car runs off memory to preset the mix. some even come with a heater, (4wires) to help your car spend less time in open loop!

either
titania which is the variable resistor
or a galvanic battery that produces voltage.

I think up to five volts
basically as a signal to help the computer vary the air and fual mixture. it is never a perfect reading you measure it for the duty cycle (on vs off time)
 

·
Registered
MercedesBenz190D 2.5
Joined
·
1 Posts
Gasoline engines run best when the air-fuel mixture is correct. The air-fuel mixture must be controlled to reduce exhaust pollutant emissions. Lowest emissions are achieved with a slightly lean mixture. The catalytic converter, an essential part for emission control, also likes a controlled lean air-fuel mixture. The oxygen sensor detects the air-fuel mixture of a gasoline engine by measuring the amount of oxygen in the exhaust gas. The fuel-injection system will trim the mixture richer or leaner based on the signal from the oxygen sensor. The typical installation is in the exhaust manifold, where the hot exhaust gases will pass by it. High temperature(>350 C) is required for the sensor to operate. My car has a heated sensor, so the sensor starts to work very quickly after the engine has started. It has three wires. Two are for the heater, and one is the sensor output. The metal case of the sensor is grounded and is the return for the sensor's output. Unheated sensors have one or two wires. I do not know the exact composition of the sensor, but I do know how it is constructed and how it operates. A ceramic-like material is exposed to the exhaust gas on one side, and to the outside air on the other. A voltage is produced as oxygen travels through the material. A rich mixture will produce almost 900 millivolts. A lean mixture produces about 100 millivolts or less. The sensor does not produce in-between voltages with any regularity. I think the material in the sensor is made to match the optimum air-fuel mixture, and the output of the sensor is pretty much on or off(too rich or too lean). The car's fuel-injection system picks a voltage to compare with, and modifies the mixture to try to maintain an on-off ratio close to 50%, so if you averaged the voltage over time it would be about 400 or 450 mV. The on-off transitions occur about one or two times per second in my car when it's running properly. When the sensor is cold, no voltage is produced, and the sensor is an open circuit with almost infinite resistance. When the sensor heats up, the impedance drops and it can produce a little bit of current. If I had to guess, I'd say that mine has an impedance of about 5000 ohms when hot. The car presents a very high impedance load, in the megohms.
 
1 - 5 of 5 Posts
Top