Haltech E6M - Manual (Page 89)

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CHAPTER 15 CLOSED LOOP CONTROL
15.1 Description
By fitting an oxygen sensor to the exhaust system of an engine, the E6H/E6M is able to
perform a feedback correction to maintain a consistent air-fuel ratio around stoichiometric
mix; i.e.. when exactly the correct amount of fuel is provided to consume all the oxygen of the
air drawn into the engine, without any unburnt fuel remaining after combustion. Using closed
loop fuel control adapts for small variations in fuel quality and day-to-day running, provides
better fuel economy and lower emissions.
Figure 15.1 Typical lambda sensor output.
An oxygen sensor (or lambda sensor) is placed in the exhaust gas stream usually after the
collector but before the catalytic converter. The O2 sensor possesses an output voltage
characteristic similar to that in figure 15-1. When the exhaust gas is free from oxygen (i.e..
mixture is rich), the sensor reads around 1 volt. When there is an excess of oxygen, the sensor
reads closer to 0 volts. Most oxygen sensors' transfer curves change very suddenly around
stoichiometric mixtures.
The object in closed loop control is to measure the voltage of the oxygen sensor, determine
whether the engine is running lean or rich, and compensate accordingly by adjusting the
injection time. The ECU may overcorrect slightly, and then will pull the mixture back towards
the desired air-fuel ratio. This slight oscillation either side of stoichiometric mixture aids the
function of the catalytic converter.
15.2 Using Closed Loop Control
In order to use the closed loop fuel control function, you must have the following:
- an appropriate lambda sensor mounted in the exhaust stream;
- E6H/E6M programming software and cable.
Mounting and connection of the sensor is all that is required in installation. Check figure 15-2
for appropriate wiring for different oxygen sensors. Run the E6H/E6M programming software