Rover's Vikingship The Lucas Electronic
Fuel Injection
part three
Rover's Vikingship


This part of site is an attempt to organize and add to the web resources for the Rover SD1 to form a cohesive and easily usable guide for those of us without easy access to expert repair and/or advice. It is not offered in any way as a definitive source and we take no responsibility for any errors that may exist.
the webmaster Rene Winters.


EGR Valve
To end this second part of the programme let's look briefly at the ancillary emission control equipment. First exhaust gas recirculation, the EGR valve dilutes the air/fuel mixture by returning a proportion of the exhaust gas to the inlet manifold. The lower peak combustion temperatures reduce the formation of nitrogen oxides.
The valve is operated by manifold depression and exhaust back pressure. It is therefore, sensitive to engine load.
Depression is sensed at this throttle edge tapping and is transmitted to the valve, through a hose.

Overrun Valve

Next the overrun valve, its function is to maintain satisfactory combustion during deceleration. The valve is mounted on the plenum chamber and is operated by manifold depression.
When depression reaches a critical level, a disc valve opens against spring pressure, and allows metered air to bypass the closed throttle plate. When depression falls, the spring ensures the bypass channel is closed.
Evaporative Emission Control
3 Finally, to prevent fuel vapour entering the atmosphere, two charcoal canisters are fitted in the fuel tank vent pipe.
A vapour separator prevents liquid fuel entering the pipe.
The canisters are also connected to the crankcase and to the throttle body. This arrangement not only ensures combustion of both oil and fuel vapour, but also, after the engine has stopped, any resultant vapour is absorbed by the canisters.

The Electrical Circuit

First let's introduce the combined relay, it is the link between the ECU and the injection system.
When the ignition is switched on, the main section of the combined relay is energised. It supplies current to the ECU switching it on.
When the engine is cranked, the main section of the relay supplies current, via the power resistor pack, to the injectors. The injectors open as their separate earth paths are completed by the ECU.
At the same time, current from the starter relay energises the pump section of the combined relay. The relay completes the circuit through the inertia switch to the fuel pump; this providing the initial fuel supply.
Apart from this, the pump section of the relay instructs the ECU to extend the injection period, thus enriching the mixture, it also completes the circuit through the extra air valve heater coil, to earth, via the ECU: and it supplies current to the thermal time switch and the cold-start injector. Providing the engine is cold, finely atomised fuel is sprayed into the plenum chamber.
As soon as the engine fires, air drawn into the manifold causes the flap in the airflow meter to be deflected. The pump contacts close and energise the pump section of the combined relay. This replaces the initial cranking current and provides a supply to the fuel pump and the heater coil in the extra air valve.

While the engine is running, the injectors open at a frequency determined by the pulse chain from the ignition coil negative terminal, sensed at the ballast resistor.
The duration of each injection being determined by the signals received by the ECU, from the airflow meter and air temperature sensor; the throttle potentiometer, the coolant temperature sensor and the lambda sensors.
As the engine warms up, the electrical resistance of the coolant temperature sensor drops, and the ECU gradually weakens the mixture by shortening the injection period.
At normal running temperature, the only effect of the coolant temperature sensor, is to instruct the ECU to cut the power supply to the extra air valve. The coolant temperature is now sufficient to keep the throttle bypass channel closed.
As you know the output voltage from a battery depends on its state of charge and the electrical load. To compensate for this, the ECU continuously monitors battery voltage and generates a correction factor. which is then applied to the injector opening pulses. This means that fuel delivery is unaffected over a wide voltage range.

Lucas EFi part I
Lucas EFi part II
Lucas EFi part IV



© rwp dec 2003