900 L4-1985cc 2.0L SOHC (1988)
Lambda Control Unit: Description and Operation
The ECU controls fuel system by means of the following main functions: Oxygen sensor monitoring; Comparator; Integrator; Signal amplifier
(Output stage).
The monitoring function checks that the operation of the oxygen sensor and the modulating valve control function coincide with the programmed
values. If incorrect values are received or a problem is detected, the control function is disabled and a fixed pulse ratio of 50% is selected for the
modulating valve. Different fixed pulse ratios can be selected if certain terminals in the ECU are grounded.
The control function of the comparator is governed by the relationship between the actual sensor voltage and the preprogrammed reference voltage in
the comparator. If the mixture is lean, the signal voltage from the oxygen sensor will be lower than the reference voltage and the ECU will then increase
the pulse ratio of the modulating valve, thereby enriching the mixture.
The integrator controls the signal voltage from the output stage at a programmed control speed to adjust the fuel mixture. The control speed is
optimized to provide best possible conversion of the exhaust gases in the catalytic converter, by keeping the Lambda value as close to 1 as possible
(ideal mixture - 14.7 to 1).
