Engine management system - PGM-Fi (All cars): Description and operation

Throttle angle sensor

Vehicle speed transducer

The fast idle control solenoid system supplements the electronic air control valve (EACV) operation during extreme low temperature conditions. The solenoid windings receive an ignition feed from the ignition switch, which is earthed by the E.C.U. when additional fast idle is required.

When the coolant temperature drops below – 10°C (14°F) and the engine speed below 1,800 rev/min, the E.C.U. earths the solenoid windings. The fast idle valve then opens allowing additional air to by – pass the throttle valve increasing the fast idle speed. The E.C.U. will then implement the electronic air control valve (EACV) to fine tune the fast idle speed.

All cars

A throttle control system, consisting of a diaphragm, closes the throttle slowly during gear changing or deceleration reducing exhaust emissions.

The throttle body incorporates a throttle valve activated by the throttle pedal. A by – pass passage around the throttle valve incorporating an adjusting screw enables the air flow at idle to be adjusted.

Note: The throttle stop screw is pre – set at the factory and should not be altered in service.

To reduce exhaust emissions a throttle dashpot diaphragm is fitted, slowing down the release of the throttle valve during deceleration and gear changing.

Throttle control system

The throttle control system consists of dashpot diaphragm, incorporating a spring and vacuum chamber connected to the inlet manifold. The dashpot diaphragm is connected to the throttle valve lever. During acceleration when manifold depression is low, only a small vacuum is present above the dashpot diaphragm. The diaphragm spring then applies a pressure on the throttle lever and the throttle valve is held partially open.

When the throttle is released during gear changing or deceleration a depression is created above the dashpot. This depression compresses the spring and the throttle valve fully closes. This operation momentarily increases air flow into the engine when the throttle is released, reducing exhaust emissions.

Note: As the throttle is partially open when the engine is switched off, vacuum must be applied to the dashpot diaphragm, when checking throttle cable adjustments.

Catalyst equipment

Oxygen sensor

An oxygen sensor is fitted to the engine exhaust manifold, to detect the amount of oxygen in the exhaust gases and send signals to the E.C.U. The E.C.U. interprets the signals and varies the duration during which the fuel is injected accordingly.

Non – evaporative loss equipment

Charcoal canister

A charcoal canister is used for the temporary storage of fuel vapour from the fuel tank until the vapour can be purged from the canister into the engine and burned.

The charcoal canister is purged by drawing fresh air in through the purge air hose, through the canister and into a port on the throttle housing.

Vapour purge control valve

A purge control valve on the top of the canister is operated by manifold depression. A thermostatic valve in the vacuum line prevents the purge control valve from opening when the coolant temperature is below a predetermined limit.