Manifold Pressure Control System

COLD ENGINE
With the engine coolant below 38"C, the manifold pressure signal to the ECU is switched by means of a solenoid vacuum valve, via a delay valve, to a port in the 'A' bank intake throttle housing. This port is located so that manifold pressure is not available to the ECU when the throttles are closed. As the throttles are opened from the idle position, exposing the port to manifold pressure, the pressure signal is supplied to the ECU via a delay valve and solenoid valve located under the 'rear of 'A' bank manifold. This has the effect of reducing the rate of ignition advance on acceleration following a cold start, and so effects a reduction in exhaust emissions under these conditions.

HOT ENGINE
When the engine coolant exceeds 45'C, the manifold pressure signal to the ECU is switched by means of a coolant temperature switch (located at the rear of the 'A' bank coolant rail} and the solenoid vacuum valve from the throttle edge port to the intake manifold. This allows full manifold pressure to the ECU under all conditions and when required a maximum ignition advance.