Viper GTS V10-8.0L VIN E (1999)
The input from the upstream heated oxygen sensor tells the PCM the oxygen content of the exhaust gas. Based on this input, the PCM fine tunes
the air-fuel ratio by adjusting injector pulse width.
The sensor input switches from 0 to 1 volt, depending upon the oxygen content of the exhaust gas in the exhaust manifold. When a large amount
of oxygen is present (caused by a lean air-fuel mixture), the sensor produces voltage as low as 0.1 volt. When there is a lesser amount of oxygen
present (rich air- fuel mixture) the sensor produces a voltage as high as 1.0 volt. By monitoring the oxygen content and converting it to electrical
voltage, the sensor acts as a rich-lean switch.
The heating element in the sensor provides heat to the sensor ceramic element. Heating the sensor allows the system to enter into closed loop
operation sooner. Also, it allows the system to remain in closed loop operation during periods of extended idle.
In Closed Loop, the PCM adjusts injector pulse width based on the upstream heated oxygen sensor input along with other inputs. In Open Loop,
the PCM adjusts injector pulse width based on preprogrammed (fixed) values and inputs from other sensors.
Downstream Oxygen Sensor 1/2
The Downstream O2 Sensor has two functions. One function is measuring catalyst efficiency. This is an OBD II requirement. The oxygen content
of the exhaust gasses has significantly less fluctuation than at the inlet if the converter is working properly. The PCM compares upstream and
Downstream O2 Sensor switch rates under specific operating conditions to determine if the catalyst is functioning properly.
The other function is a downstream fuel control which was introduced in 1996. The upstream O2 goal varies within the window of operation of the
O2 Sensor. In the past the goal was a preprogrammed fixed value based upon where it believed the catalyst operated most efficiently.
While the Upstream O2 Sensor input is used to maintain the 14.7:1 air/fuel ratio, variations in engines, exhaust systems and catalytic converters
may cause this ratio to not be the most ideal for a particular catalyst and engine. To help maintain the catalyst operating at maximum efficiency,
the PCM will fine tune the air/fuel ratio entering the catalyst based upon the oxygen content leaving the catalyst. This is accomplished by
modifying the Upstream O2 Sensor voltage goal.
If the exhaust leaving the catalyst has too much oxygen (lean ) the PCM increases the upstream O2 goal which increases fuel in the mixture
causing less oxygen to be left over. Conversely, if the oxygen content leaving the catalyst has is too little oxygen (rich) the PCM decreases the
upstream O2 goal down which removes fuel from the mixture causing more oxygen to be left over. This function only occurs during downstream
closed loop mode operation.
