Fuel Delivery and Air Induction: Description and Operation
FUEL SYSTEMDescription
The fuel system used is the recirculatory type. The fuel tank is mounted across the car behind the rear passenger seats.
Fuel is drawn from the fuel tank into the in-tank fuel module by the fuel pump, with the fuel passing through a venturi on the fuel pump pressure side.
A 70 micron filter is incorporated at the inlet port of the module to prevent ingress of particle contaminants. A further 400 micron rock filter is included at the inlet port of the fuel pump to prevent the passage of smaller participle contaminants into the fuel pump and the rest of the fuel system.
Fuel is pumped from the base of the fuel tank through a flexible hose to an in-line filter. From the filter, fuel flows through underfloor pipework to the front of the vehicle where a flexible hose connects the underfloor feed pipe to the inlet port of the fuel rail.
The fuel rail is mounted on the engine and has a fuel pressure regulator attached at the return port. The fuel pressure regulator is used to control fuel line pressure and maintains a constant delivery of fuel to the fuel injectors across the fuel rail. This is accomplished by applying inlet manifold pressure to a diaphragm within the pressure regulator.
Pressure is kept constant within the range 241.30 - 310.25 kN/m2 (35 - 45 lb/in).
Unused fuel from the engine is returned to the in-tank module through return hoses and underfloor piping. A 70 micron filter is used in the return inlet of the module to capture debris that may be present in the fuel rail or return line at initial start-up and so prevent it from entering the system. Both the feed and return ports of the module use non-return valves for safety.
Electronic Fuel Injection
A digital type Electronic Control Unit (ECU) with an integral manifold pressure sensor, governs the amount of fuel injected. The manifold pressure and speed signal derived from ignition pulses, provide the main control for the fuel injected. Additional sensors are used to monitor engine temperature, inlet air temperature and throttle position, thereby ensuring optimum fuelling is computed for all engine operating conditions.
Fuel Control System
The metering of fuel is controlled by regulating the time that the injectors are open during each engine cycle. The frequency of the injectors is dependent on engine speed and conditions. The basic pulse length is mapped against speed and intake manifold pressure which is sensed by a transducer located in the electronic control unit and linked to the intake manifold by a pipe. Information on engine speed is derived from the ignition trigger pulses in the ignition system.
The injectors are fired six times per engine cycle, this operation being triggered from the output of the ECU.
The injectors are energized for a time proportional to the figure given on the base map plus a constant of proportionality which is varied according to secondary control parameters, i.e. engine coolant temperature, inlet air temperature, throttle movement and position, and battery voltage.
The fuel pump is energized only when the ECU senses an engine cranking signal or an engine running signal. This prevents the engine being flooded with fuel in the event of an injector sticking open.
Cranking Fuelling
Cranking fuelling provides six injections per engine cycle instead of the normal two. This reduces after a set number of injections.
Coolant Temperature Enrichment
Temperature enrichment is provided during starting and warm-up. This is achieved by increasing the injector "on" time above that of basic requirements and is implemented by the ECU in response to an input from the coolant temperature sensor. The enrichment is reduced with increasing engine speed and load.
After-start Enrichment
After-start enrichment is provided to supply added fuel during warm-up. The enrichment is coolant temperature dependant (the colder the temperature, the more fuel is supplied). This is achieved by the ECU which increases the injector "on" time above that of basic requirements and then decreases the amount of additional fuel supplied at a fixed rate over a number of engine revolutions.
Temperature Sensors
The temperature of the air taken into the engine through the inlet manifold and the temperature of the coolant in the cylinder block are constantly monitored. The information is fed directly to the ECU.
The air temperature sensor has a small effect on the injector pulse width, and should be regarded as a trimming rather than a control device. It ensures that the fuel supplied is directly related to the weight of air drawn in by the engine. Therefore, as the weight (density) of the air charge increases with a falling temperature, so the amount of fuel supplied is also increased to maintain optimum fuel/air ratio.
The coolant temperature sensor has a greater control although it functions mainly while the engine is initially warming-up.
Full Load Fuelling
To obtain maximum engine power it is necessary to inhibit the "closed loop" system and simultaneously increase the fuelling level. This is determined by throttle position and engine speed.
Flooding Protection System
When the ignition is switched on, but the engine is not cranking, the fuel pump will run for two seconds to raise the pressure in the fuel rail; it is then automatically switched off by the ECU. Only after cranking has started is the fuel pump switched on again. Switching control is built into the ECU circuitry. This system prevents flooding if any injectors become faulty (remain open) when the ignition is left on.
Engine Load Sensing
The driver controls engine power output by varying the throttle opening and therefore the flow of air into the engine. The airflow determines the pressure that exists within the plenum chamber, this pressure therefore is a measure of the demand upon the engine. The pressure is also used to provide the principle control of fuel quantity, being converted by the manifold pressure sensor in the ECU into an electrical signal. This signal varies the width of the injector operating pulse as appropriate. The pressure sensor is fitted with a separate diaphragm system that compensates for ambient barometric variations.
Fuel Pump 1 In-tank Module
Fig. 1 Fuel Pump Module:
The fuel pump is fitted inside the in-tank module (1 Fig. 1), which is fixed to the centre base of the fuel tank, via a rubber cradle (2 Fig. 1) and steel bracket (6 Fig. 1). The rubber cradle behaves as an acoustic baffle to deaden pump vibration and noise. There are three large tabs (3 Fig. 1) and one small tab on the module casing, which locate into slots in the centre recess of the rubber mounting (4 Fig. 1) this ensures that the pump can only be mounted in the correct orientation. The periphery of the rubber mounting incorporates four protrusions each having a locating slot (5 Fig. 1), three slots are large and one is small, which locate onto tabs on the steel support bracket (7 Fig. 1).
NOTE: It is important to ensure correct orientation and fitting of fuel pump module with rubber mounting and steel support bracket.
Fig. 2 Filter:
The fuel pump draws fuel into the module from the fuel tank through a filter in the base of the module (1 Fig. 2).
Fuel is pumped out of the module through a port at the top of the module (9 Fig. 1). There are two rubber moulded hoses connected to the top of the module, the short hose (10 Fig. 1) connects from the module's outlet port to the underfloor fuel feed pipe at the base of the fuel tank. The long hose (11 Fig. 1) connects the fuel return pipe to the module's return port.
Connections between the hoses and solid pipes are underneath the car. The only direct connection between pump module and the tank is at the evaporative loss flange via a two wire electrical connection (12 Fig. 1).
The pump delivers approximately 120 Liters/min. @ 3 Bar.
The complete fuel pump module is replaced when renewing the fuel pump.
Fuel Filter
The main in-line fuel filter is mounted underfloor the left-hand side of the vehicle forward of the axle carrier. The unit is made from stainless steel.
CAUTION: Directions for fuel flow are shown on the filter, it is important that the filter is connected the correct way round.
Evaporative Loss Flange
Evaporative Loss Flange:
The flange is mounted to the tank by a seal and locking ring, it has three external outlet ports and one electrical connection.
The large port (1 Fig. 1) allows the tank to vent vapor during refuelling and is directly connected to the fuel filler neck.
The intermediate port (2 Fig. 1) has a "Legris" quick-fit connector moulding and allows for over pressurization; it is connected to atmosphere by a nylon pipe the outlet of which is underneath the vehicle.
The small outlet port (3 Fig. 1) is used for vehicles incorporating evaporative loss control and uses a nylon pipe to connect the tank to the charcoal canister located at the front of the vehicle. For cars not fitted with evaporative loss control, the pipe is vented directly to atmosphere via a hose passing underneath the car. In both evaporative loss control vehicles and non-evaporative loss control vehicles, a Rochester valve is included in the line, controlled by manifold pressure.
Connectors and Hoses
Legris Connectors:
Legris quick-fit connectors are used throughout the fuel system (Fig. 2). At connections between hoses and the underfloor pipes, the pipes have a ridge or paint line to indicate how far the connector should be pushed onto the pipe end.
CAUTION: Pipes and component stubs must be fully inserted into connector ends to ensure proper fit; failure to do so could cause fuel leakage.
There are two sizes of connector, 8mm and 10mm, this is to ensure that the feed pipe is not connected as the return pipe and vice versa. The 10mm connector is used for the feed line.
To release connectors, push and hold the locking ring (1 Fig. 2) towards the connector fitting while moving the connector and pipe end apart.
Always ensure pipe connectors are pushed fully home when refitting by having the pipe shoulder (2 Fig. 2) abut the locking ring.
In-tank fuel hoses
Service tool JD 175 is available for the tightening of jubilee clips which attach feed and return hoses to the in-tank module.
Throttle Potentiometer
Throttle Position Switch:
To ensure the vehicle road performance is satisfactory, with good throttle response, acceleration enrichment is necessary. Signals are provided by the throttle potentiometer (Fig 1), which is mounted on the throttle spindle and indicates the throttle position to the ECU. When the throttle is opened the fuelling is enriched and when closed the fuelling is weakened. When the throttle is opened very quickly, all the injectors are simultaneously energized for one pulse.
This ensures that there is enough fuel available at the inlet ports for the air admitted by the sudden opening of the throttle. The duration of this extra pulse is controlled by the engine temperature signal, and is longer with a cold engine.
Lengthening the normal injection pulses is done in proportion to the rate at which the throttle is opened and it takes a short time to decay when the throttle movement stops. Enrichment in this way is also varied according to the engine temperature. The fuel cut off function is controlled by the throttle potentiometer, and the conditions under which it occurs are programmed into the ECU memory.
Injectors
Fuel Injector:
Each fuel injector (Fig. 2) consists of a solenoid operated needle valve with the movable plunger rigidly attached to the nozzle needle. In the closed position, a helical compression spring holds the needle against the valve seat.
The injectors have a solenoid winding mounted in the rear section of the valve body, with a guide for the nozzle needle in the front section.
The injectors are operated in two stages, initially they are operated via a pull-in circuit, then when the injectors are open a change to a hold on circuit is made via current limiting resistors for the remainder of the injection period as determined by the ECU. In this way the heating effect on the output transistors of the ECU is reduced. It also ensures a rapid response from the injectors.
The metering of fuel is controlled by regulating the time that the injectors are open during each engine cycle. The frequency of the injectors is dependent on engine speed and conditions. The basic pulse length is mapped against speed and intake manifold pressure which is sensed by a transducer located in the electronic control unit and linked to the intake manifold by a pipe. Information on engine speed is derived from the ignition trigger pulses in the ignition system.
The injectors are energized for a time proportional to the figure given on the base map plus a constant of proportionality which is varied according to secondary control parameters, i.e. engine coolant temperature, inlet air temperature, throttle movement and position and battery voltage.
Fuel Pressure Regulator
Fuel Pressure Regulator:
The fuel pressure regulator (Fig. 1) is attached to the fuel rail and consists of a metal housing containing a spring loaded diaphragm. When the pressure setting of the regulator is exceeded, the diaphragm moves, exposing an opening to an overflow duct which allows excess fuel to return to the fuel tank, causing a drop in fuel pressure. The reduced fuel pressure allows the diaphragm to move back to its original position, thereby closing the fuel return outlet. This sequence of events is repeated as long as the pump is running. In this way, fuel pressure is held constant as fuel demand varies. The pressure setting is adjusted to the correct value during production when the outer spring housing is compressed until the correct spring load is obtained. This is not adjustable in service.
The spring housing of the regulator is sealed and connected to the engine inlet manifold by a small bore pipe. By allowing it to sense inlet manifold depression, the pressure drop across the injector nozzle remains constant because the fuel pressure will alter as manifold depression alters. This arrangement ensures that the amount of fuel injected is only dependent on the the duration of injector open time.
System fuel pressure is 3 bar (43.5 in/lb) above manifold pressure.
Fuel Rail
The fuel rail is mounted and secured to the inlet manifold casting. The six injectors are directly fitted to the rail via O-ring seals and secured by retaining clips.
Fuel is fed into the rear of the rail and fuel flow pressure across all injectors is controlled by the pressure regulator valve mounted at the front rail.
ENGINE COMPARTMENT COMPONENT LOCATION
1. Injector
2. Fuel rail
3. Pressure regulator
4. Fuel return pipe
5. Air cleaner assembly
6. Throttle actuator
7. Throttle potentiometer
8. Throttle housing assembly
9. Vacuum pump
10. Vacuum dump valve
11. Throttle pedestal assembly
12. Throttle linkage
13. Fuel feed pipe
14. Throttle cable
FUEL TANK ASSEMBLY (COUPE)
1. Tank unit
2. Tank breather hose
3. Flange locking ring
4. Evaporative loss flange
5. Flange seal
6. Internal feed and return hoses
7. Pump module
8. Mounting rubber
9. Drain plug
10. Gauge unit locking ring
11. Fuel gauge sender unit
12. Gauge unit seal