Fuel Delivery and Air Induction: Description and Operation
V8 Fuel Delivery System
Fuel Delivery System Components
the Land Rover V8 fuel delivery system comprises the following main components:
- Saddle type fuel tank
- Fuel injectors
- Non return fuel rail
- Fuel pump
- On board refuelling vapor recovery system (NAS only)
- Tank leakage detection system (NAS only).
Fuel Tank
the fuel tank is constructed from moulded plastic and is mounted under the rear seat just forward of the rear axle. the fuel tank has a 100 Litre capacity and activates a low fuel warning lamp in the instrument pack when there is 12 liters in the tank. the tank is of the saddle tank design with a siphon jet pump in the left side to transfer fuel to the right side where the fuel pump is mounted. the fuel is delivered along pipes that run along the underside of the vehicle to a fuel rail mounted on the engine.
Fuel Filter
the fuel filter/pressure regulator is mounted in on the lower right hand side of the tank. the charcoal canister is mounted at the front of the tank on the right hand side. the components are covered by a plastic under tray to protect them when driving off-road. the undertray has an inspection cover to enable access to the charcoal canister and the fuel filter.
Fuel Pump
the fuel pump comprises a pump sender unit pot and venturi. the unit has an integral filter inside the pot. the pump unit operates at 3.5 bar for 170-205 l/hr (the V8 has a maximum operating requirement of 90 l/hr).
the pump is controlled by the ECM via the fuel pump relay.
Should the fuel pump electrical connection need to be disconnected, it is imperative that the ignition should be switched off. If the ignition is on in any position the fuel gauge will memorize its last needle position prior to power down. Once power is restored the gauge will display the last remembered position regardless of the actual level of fuel in the tank. This will result in incorrect fuel gauge readings if the fuel tank has been drained and not filled worth exactly the same quantity of fuel that was removed.
Injectors
An electromagnetic, top feed fuel injector is installed in each cylinder inlet tract of the inlet manifolds. A common fuel rail supplies the injectors with fuel from a returnless fuel delivery system. the fuel in the fuel rail is maintained at a pressure of 3.5 bar by a pressure regulator incorporated in the fuel filter Unit on the side of the fuel tank. A Schraeder valve is installed in the fuel rail, to the rear of injector No.7, to enable the fuel pressure to be checked.
Fuel rail
A contoured steel tube common fuel rail, supplies the injectors with fuel from the returnless fuel delivery system. the fuel in the fuel rail is maintained at a pressure of 3.5 bar by a pressure regulator incorporated into the fuel filter.
Tank Leakage Detection (NAS Only)
New Range Rover is equipped with a tank leakage detection system. the system is controlled by the ECM.
the tank leakage detection module is located inside the wheel arch at the top of the wheel arch next to the fuel filler neck on a metal bracket.
Leak Detection Normal Operation
In its inactive state, filtered fresh air enters the evaporative system through the sprung open valve of the tank leakage detection module. When the ECM activates the tank detection module for leak testing, it first activates only the pump motor. This pumps air through a reference orifice (0.5 mm) which causes the electric motor to draw a specific amperage value. This value is then equivalent to the size of the reference orifice. the solenoid valve is then energized which seals the EVAP system and directs the pump output to pressurize the EVAP system.
the system is detected as having a large leak if the amperage value is not realized, a small leak if the same reference amperage is realized or no leak if the amperage value is higher than the reference leak value.
the leak detection module ensures accurate fuel system leak detection for leaks as small as 0.5mm. the pump contains an integral DC motor which is activated directly by the engine control module. the ECM monitors the pump motor operating current as the measurement for detecting leaks.
In its inactive state the pump motor and the change over valve of the DC Motor LDP are not energized. When purge valve operation occurs filtered air enters the fuel system compensating for engine vacuum drawing on the hydrocarbon vapors stored in the charcoal canister.
the ECM only initiates a leak diagnosis test every second time the criteria are met. the criteria are as follows:
- Engine OFF with ignition switched OFF
- Engine Control Module still in active state or what is known as "follow up mode"(Main Relay energized, control module and ECM components on-line for extended period after key off)
- Prior to Engine/Ignition switch OFF condition, vehicle must have been driven for a minimum of 20 minutes.
- Prior to minimum 20 minute drive, the vehicle must have been OFF for a minimum of 5 hours.
- Fuel Tank Capacity must be between 15 and 85% (safe approximation between 1/4 - 3/4 of a tank)
- Ambient Air Temperature between 7°C & 35°C (20°F & 95°F)
- Altitude < 2500m (8,202 feet)
- Battery Voltage between 11.5 and 14.5 Volts.
When these criteria are satisfied every second time, the ECM will start the Fuel System Leak Diagnosis Test. the test will typically be carried out once a day i.e. once after driving to work in the morning, when driving home in the evening the criteria are once again met but the test is not initiated. the following morning the test will run again.
Phase 1-Reference Measurement
the ECM activates the pump motor. the pump pulls air from the filtered air inlet and passes it through a precise 0.5mm reference orifice in the pump assembly.
the ECM simultaneously monitors the pump motor current flow. the motor current raises quickly and levels off (stabilizes) due to the orifice restriction. the ECM stores the stabilized amperage value in memory. the stored amperage value is the electrical equivalent of a 0.5 mm (0.020 inch) leak.
Phase 2-Leak Detection
the ECM energizes the Change Over Valve allowing the pressurized air to enter the fuel system through the Charcoal Canister. the ECM monitors the current flow and compares it with the stored reference measurement over a duration of time.
Once the test is concluded the ECM stops the pump motor and immediately de-energizes the change over valve. This allows the stored pressure to vent thorough the charcoal canister trapping hydrocarbon vapor and venting air to atmosphere through the filter.
Test Results
the time duration varies between 45 & 270 seconds depending on the resulting leak diagnosis test results (developed tank pressure "amperage" within a specific time period). However the chart above depicts the logic used to determine fuel system leaks.