Rover SD1 V8 EFI, Vitesse and Rover EFi models
INTRODUCTION
Electronic fuel injection.
The RoverV8 fuel injection system fitted as alternative to carburetors compromise of two parts: a fuel injection system and an electronic control for the fuel injection system.
Components.
At 2.5 kgf/cm2 fuel is drawn from the fuel tank at the rear of the car by an electric fuel pump located beneath the car floor. The pump will only operate when the ignition and the starter motor circuits are energized. From the fuel pump fuel passes through fuel filters located in the engine compartment to a pressure regulator, the spring chamber of which is connected to the engine the engine intake manifold. As a result, the difference between the intake manifold pressure and the fuel pressure is held constant, excess fuel being returned to the fuel tank via an anti surge pot.
A fuel rail links the pressure regulator with the fuel injectors being fitted to each inlet manifold spur. The injectors may be either open or closed and are solenoid operated. A relays actuated by the ignition circuit energize the injectors and are pulsed to "open" by the electronic control unit. When the "open" injectors spray fuel into the inlet manifold to be drawn into the engine cylinders at the next stroke of the working cycle.
Therefore there needs to be no fixed relationship between the injector timing and the engine ignition or valve timing. The injectors are programmed to "open" in banks of four, in unison, twice per engine-operated cycle. (2 revolutions). On eight cylinder engines the two banks of four injectors operate alternately. The time that the injectors are "open" governs the amount of fuel supplied to the engine and the electronic control unit from the input it receives from various sensors computes this 'open' time.
To assist cold starting, a separate cold start injector sprays a fine jet of fuel against the air stream entering the plenum chamber before the main injectors add fuel to it. The cold start injector is energized from the engine starter motor circuit and has in series with it a thermotime switch, this switch is dual activated by the engine coolant temperature (heat) and a heater coil around a bi-metal strip (time), the coil being energized from the starter motor circuit. The purpose of the thermotime switch is to ensure that the cold start injector will not be energized when the engine is at normal operating temperature or should the starter motor be used for prolonged periods when the engine is below normal operating temperature. Thus the switch prevents extra fuel being supplied to the engine when it is not required. The switch will isolate the cold start injector after approximately 8 to 12 seconds at –20 C decreasing this time as the engine approaches its normal operating temperature.
DESCRIPTION
Fuel System
The electric pump (P) draws fuel from the fuel tank (see fig.1.1). The pump passes the fuel along the fuel supply pipe (8), through a fine mesh (2 micron) in-line filter (F) to the injector rail and injectors (1 -8).
Fuel pressure is controlled by the regulator (R) and excess fuel returns to the fuel tank via the return pipe (E).
Fuel enters the engine via eight injectors, one for each cylinder, and the fuel is injected indirectly.
This means that fuel is not injected directly into the' combustion chambers.
The amount of fuel delivered by the injectors is governed by the period of time they are open - the longer the 'open' time, the greater the amount of
fuel delivered.
The injectors operate in two banks of four; each bank operates alternately, with both banks operating twice per working cycle.
Air System
Without air in the correct volume, the fuel will not burn efficiently; therefore a sophisticated air control system is also necessary. Electronics System
The Electronic Control Unit (ECU) illustrated in fig.1.3 controls the injector 'open' time (duration). The ECU is a solid state computer; it receives information from a number of sensor sources - engine speed, engine temperature, ambient temperature, throttle position, air flow etc. It compares this information with data already programmed into it, to inject the correct amount of fuel by controlling the injector 'open' time.
The driver's accelerator pedal operates a throttle butterfly (T), as seen in fig.1.2, located in the air intake tract. From there the air passes to a plenum
chamber (PC) located centrally over the engine and from which the air is drawn through ram pipes into the inlet manifold itself.
However, before the air reaches the throttle butterfly it is drawn through the air flow meter (A). The air flow meter is a vital part of the EFI system; it measures the volume and mass of air being drawn into the engine, and takes into account the air temperature.
Now let us look at the function of the components within each system, and see how they contribute to the overall operation of 'Electronic Fuel Injection';
we will start with the fuel system.
FUEL SYSTEM OPERATION
Fuel Pump
The electric fuel pump, located in front of the fuel tank, is a roller type pump operated by a permanent magnet motor. The armature and bearings are cooled and lubricated by the fuel flowing through the pump with no risk of combustion because the pump never contains an ignitable mixture, even when the tank empties
Fig.2.1 shows an eccentric rotor (RT) mounted on the armature shaft with rollers (RO) in pockets rotating within a housing (H). When the motor is energised centrifugal force acting on the rollers forces them outward to act as seals. The fuel between the rollers is forced to the high-pressure side of the system(HP).
A pressure relief valve (PR) is located within the roller pump (RP) prior to the armature (A) and protects the pump from over -pressurising. A non-return
valve (NR) is located in the pump outlet to the filter and injectors; it prevents fuel draining from the injector supply pipe.
Fuel gravitates through a filter in the tank to the pump inlet and into the roller pump ensuring that the system is primed. The roller pump generates the necessary fuel pressure to feed the injection system. Excess pressure opens the relief valve allowing fuel to recirculate to the pump input.
Fuel Filter
The fuel filter is mounted on the nls inner wing forward of the bulkhead. It is a 2 micron, fine mesh unit that must be changed at stipulated service intervals. It must be fitted the correct way round; the arrow on the filter body shows the direction of fuel flow, when installed.
Fuel Pressure Regulator
The fuel pressure regulator is fitted to control the pressure of fuel delivered at the injectors by sensing variations in manifold depression; this is to ensure that the actual quantity of fuel released by the injectors is governed by one factor only - injector 'open time'.
The pressure regulator is fitted in the excess fuel return pipe (E), close to the injector fuel rail with its fuel supply (F) as seen in Fig.2.2. It has two chambers separated by a diaphragm (R1); one chamber contains fuel from the supply line (F), the other is linked by a pipe to the engine side of the throttle butterfly to sense manifold depression. In the rest position the spring (R2) holds the, diaphragm valve against the fuel return pipe.
Under conditions of low manifold depression, e.g. full throttle (Fig.2.2A), the spring continues to hold the diaphragm on its fuel return pipe seat. In these
circumstances, pump pressure must reach approximately 36lb/sq.in to move the diaphragm valve against spring pressure and allow excess fuel to return to the tank.
When manifold depression is high, e.g. idle and overrun (Fig.2.2B), the diaphragm valve is drawn against spring pressure. The fuel return is opened and the fuel pressure falls to 26 Ib/sq.in. Any intermediate depression will regulate fuel pressure between the minimum and maximum.
In this way fuel pressure varies according to manifold depression and ensures the amount of fuel delivered by the injectors is governed only by the injector 'open time me. When manifold depression is low (Fig.2.2A), fuel pressure needs to be high to ensure sufficient fuel is forced through the injector for a given injector 'open time', say 0.003 cc of fuel per 10 millisecond period.
When manifold depression is high (Fig.2.2B), the depression will try to 'suck' fuel from the injector nozzle. Therefore the fuel pressure needs to be reduced by the action of the regulator to ensure the same 0.003 co of fuel will pass through the injector in the same 10 millisecond period.
Injectors
Although the injectors are non-serviceable items, it is useful to have some knowledge of how they operate for diagnostic purposes.
Each injector contains a needle valve (A) as seen in fig.2.3, which is held closed in the rest position by a coil spring (B). When the electrical solenoid (C) is energised, it lifts the needle valve to allow the fuel to pass; and when the solenoid is de-energised, the spring snaps the needle valve closed to cut off the fuel flow.
The tip of the needle is ground to a pintle shape to ensure efficient atomisation of the fuel spray into the inlet manifold. The injector needle valve is opened when signalled by the ignition system via the ECU.
The signal to inject comes from the ignition distributor reluctor as shown fig.2.4. Only four of the reluctor gaps are used to signal 'inject'; the ECU ignores every other signal. It is the ECU, which dictates the injector 'open time' and therefore the amount. Of fuel that is injected.
A separate resistor pack is fitted in the circuit to reduce the 12 volt supply down to 3 volts at the injector; this is shown in the electrical section. Obviously if the incorrect quantity of fuel is injected, emissions, performance, economy and the customer, soon become upset. The principal sensor in the EFI system is the intake air flow meter. And we see how this operates in the next section.
AIR SYSTEM OPERATION
Air Flow Meter
The air flow meter is located between the air filter and the throttle butterfly housing. Air flowing to the engine is monitored by the air flow meter and information is sent to the ECU. Incorporated in the airflow meter is an adjustment screw to set the mixture and CO levels.
The air flow meter contains a double flap unit, which pivots on a spindle (FS) mounted in the housing. The measuring flap (MF) is closed on to its stop by a light spring (FR), and is opened by the air being drawn into the engine; as the measuring flap opens, the compensating flap (CF) moves into the damper chamber.
A potentiometer (variable resistor) (AP) is connected to the flap spindle; movement of the flap alters the value of the resistance which is signalled to the ECU. The ECU compares this signal value with its memory and, together with information from other sensors, computes the duration of the injector
'open' time.
There is one further electrical connection at the flap spindle, which is to the switch contacts (FPC) in the circuit to the fuel pump.
It can also be seen in fig.2.6 that whilst the bulk of air enters the engine via the measuring flap, a by-pass port and adjustment screw (CO) is also provided. This adjustment screw enables fine adjustment of the actual airflow and thereby controls the mixture strength (CO) at idle speeds. The throttle butterfly (TB), which controls the speed of the engine, is also equipped with a potentiometer (TP) to provide the ECU with information on throttle position.
Also shown is the throttle butterfly by-pass port and idle speed adjustment screw (IS). This screw operates in much the same way as the mixture screw, in that while some air is passing the throttle butterfly, the idle screw can be adjusted to alter the total volume of air entering the engine, in order to control the idle speed.
Let us now just concentrate on how the measuring flap is stabilised throughout the engine speed range. When the throttle is opened as seen in fig.2.7, pressure at 'B' falls due to the depression in the manifold, and atmospheric pressure 'A' moves the measuring flap to allow more air to enter the engine. At the same time the air in chamber D is momentarily compressed, thus damping the rate of movement of both flaps.
Fig. 2.7
If the throttle is now held steady, the air pressure in chamber '0' will also fall until it is equal to the pressure at 'B'. This balance of pressure on each side of the damper flap ensures that the flap unit remains stable at any throttle opening.
At maximum throttle opening as shown in fig.2.8, the flap unit will be resting against the full open stop; here depression is maintained, in chamber '0' by the rush of air passing the small gap shown at 'G.
Both flaps are in fact slightly twisted in opposite directions to the pivot spindle axis; this is to ensure
progressive pressure changes within chamber '0' and smooth movement of the flap unit when opening or closing.
Throttle Butterfly
The throttle butterfly (seen in fig.2.9) is mounted in between the plenum chamber and the air flow meter; it is linked directly to the driver's accelerator pedal.
As mentioned previously, a throttle potentiometer is mounted on the butterfly spindle similar to the potentiometer on the air flow meter spindle.
The varying resistance signals from the air flow meter and throttle potentiometers are fed to the ECU for analysis and for computation of the injector 'open' time.
The information from these two potentiometers is computed by the ECU to give a very accurate fuel/air ratio supply to the engine.
The required ratio varies dependant on a number of factors, and therefore additional devices are fitted to ensure the correct air/fuel ratio under a variety of conditions; for example, an 'extra air valve' and Injector provide a richer mixture for cold starting.
COLD START OPERATION.
During cold starts, additional air and fuel is required to provide a combustible mixture. The air is supplied to the plenum chamber via the extra air valve, which bypasses the throttle butterfly and operates in conjunction with a cold start injector to supply the additional fuel.
Extra Air Valve
The extra air valve is mounted on the inlet manifold coolant gallery in front of and to the right of the plenum chamber, and is therefore sensitive to coolant temperature.
The extra air valve contains a disc valve (DV) as seen in fig. 2.10A. and its basic design is quite simple. When cold, an aperture in the disc and an aperture in the body of the valve are in alignment, allowing air to pass through. When the temperature rises, the disc turns about its central spindle
progressively eclipsing the aperture through which the air can pass.
The disc is turned by a bi-metal (B), which responds to both ambient temperature (i.e. the coolant temperature) or to the heating wire (H) coiled
around it This coil is connected to the fuel pump electrical circuit; therefore the coil starts to heat the bi-metal and begins to close the valve as soon as the engine cranks and runs (see fig. 2.10B).
Once the engine is running, the combined effect of the heater coil and engine temperature closes the extra air valve at temperatures between 60 - lO°C.
Cold Start Fuel Injector
During cold starts an electrical supply into the ECU from the starter circuit ensures an increased 'open' time for all the injectors during cranking. However, to achieve a satisfactory start in particularly adverse conditions, a· cold start injector mounted on the R/H side of the plenum chamber is positioned to spray directly against the incoming air to give the best atomisation of the additional fuel it supplies. The cold start injector (CSI) (see fig.2.11) is controlled by a 'thermo time switch' (TT) located in the coolant gallery in the inlet manifold. This unit contains a heater coil (HC) around bi-metal operated contact points (BMC), and works as follows.
During cranking in cold conditions current can pass through the closed contact points of the thermo time switch and cause the injector to operate. At the same time current is passing through the heater coil to warm the bi-metal. After a maximum of 12 seconds the expansion of the bi-metal will open the contact points; the injector will then cease to operate to avoid an over fuelling condition.
In any case the injector will cease to operate as soon as the engine fires because it is only connected to the ignition system during cranking, and when
correctly tuned, the engine will fire and run before the maximum 12 second limit is reached. At higher ambient temperatures the operating time progressively lessens, until 35°C approximately, when the thermo time switch contact points remain open and the cold start injector will not operate.
SOLENOID AIR VALVE OPERATION
(Only fitted to vehicles with air conditioning) On vehicles fitted with air conditioning, an air supply is taken from the extra air valve pipe; this supply feeds an air valve (fig.2.12), which increases the idle speed when the air conditioning compressor cuts in. It is a sealed unit containing a solenoid-operated valve.
The solenoid is connected electrically to the compressor control circuit, and as soon as the compressor cuts in, the solenoid opens the valve to allow additional air into the engine. This causes a slight fall in manifold depression - enough to affect the fuel pressure regulator and increase the fuel pressure. The increased air/fuel mixture is sufficient to step up the idle speed and counteract the loading on the engine imposed by the compressor.
VENTILATI0N SYSTEM VACUUM SUPPLY (Only fitted to vehicles with air conditioning)
On vehicles fitted with air conditioning some of the flaps on the heater/air conditioning unit are operated by Vacuum actuators controlled from a vacuum diverter unit linked to the heater/aircon controls on the centre console.
This vacuum comes from a connection to the rear of the plenum chamber and is stored in a reservoir (VR) fig.2.13, mounted ON the N/S bulkhead.
COOLANT CONNECTIONS
For quick warm-up, a manifold hot spot (MH) fig.2.14 is fitted under the plenum chamber intake in the area of the throttle butterfly; the hot spot is
heated by coolant passing through hoses (CH) from the engine.
It is important to ensure that the ·hot spot· gasket and bolt threads are smeared with silicone sealant during assembly to ensure coolant cannot leak to the outside, or indeed past the bolt hole threads which break through into the plenum chamber throat.
The illustration also shows the vacuum advance pipe connection (VC) on the manifold side of the butterfly and the crankcase vent pipe (CV) on the intake side.
Correct Functioning of the Crankcase Ventilation System is important to the operation of EFI.
CRANKCASE VENTILATION
The crankcase ventilation system is an integral part of the air supply system to the engine, but it is often overlooked when diagnosing problems. An air leak or a blocked pipe in the ventilation system will noticeably affect engine performance.
The system works as follows:
Air is drawn out of the crankcase by depression felt at the pipe connected to the plenum chamber in the butterfly housing. This pipe connects to the front of the right rocker cover via an oil separator (OS) which is fitted to ensure that lubricating oil is not drawn into the engine inlet. As the impure air is being drawn out to be burnt in the combustion chambers, it is replaced by fresh air drawn in through the filter (F) located on the rear of the left rocker cover (see fig.2.15)
The volume of air taken into the engine in this way bypasses the air flow meter, and therefore must remain a 'constant' amount to maintain the programmed air fuel ratio. Any faults that occur within the crankcase ventilation system will affect the running of the engine. These include:
Air restriction due to blocked filter, oil separator, external pipe etc.
Excess air due to leaking gaskets etc.
Overrun valve
Having explained the fuel air and crankcase ventilation systems, we now look at the operation of the electrical sensors, which provide the information by which components carry out the commands of the ECU.
The pressure differential acting on the valve head (VH) compresses the spring (SP) centralised by the spring seats (SS). Thus, the head moves away from the valve disc (VD) which is trapped by the connection faces.
This allows air to pass from the air rail into the inlet pipe (IP) and through the valve into the plenum chamber to optimise the combustible mixture (see fig.2.16).
A nut (N) adjustment controls the spring tension, which is preset during manufacture and should not be altered. However if it has been disturbed, acceptable conditions can be restored with the nut approximately 5 turns out from fully closed.
Mounted on the side of the plenum chamber at the rear of the engine, the connection face (CF) must be airtight.
Sufficient air is provided by this valve during engine-overrun conditions to ensure good combustion.
This is necessary because the very nigh vacuum during rapid deceleration of the engine causes any residual fuel condensed on the inlet manifold and plenum chamber walls to evaporate and create an over rich mixture.
