Fuel Tank: Description and Operation

Fuel Tank and Lines

COMPONENT LOCATION

Fuel Tank And Lines:

INTRODUCTION
The major components of the 4.2L V8 fuel system comprise
- Stainless steel saddle type fuel tank
- Fuel pump
- Fuel filler pipes
- Fuel level sensors
- Fuel delivery pipes.

The fuel system uses an electronic returnless fuel system which comprises a pump module mounted in the fuel tank to deliver fuel at variable flow and pressure to the fuel rails which supply fuel to all fuel injectors. The fuel pump operation is regulated by a Fuel Pump Driver Module (FPDM) which is controlled by the engine management system. The control module regulates the flow and pressure supplied by controlling the operation of the fuel pump using a PWM output.

FUEL TANK







The fuel tank is a saddle type tank made of stainless steel pressings. The tank is located forward of the rear suspension and is mounted using two metal straps. The tank is a sealed unit with the only internal access being via the pump module flange aperture on the top of the tank.

The flange assembly comprises a pump module flange which contains all external pipe and electrical connections for the tank internal components, a collar and a clamp. The flange is fitted with a seal which locates in the tank aperture. An arrow on the flange must be aligned between two molded lines on the tank, adjacent to the pump module flange aperture, to obtain the correct orientation. The collar is located over the flange and is secured with the clamp. The flange, seal, collar and clamp arrangement meets the sealing requirements of LEV2 emissions.

The flange has a five pin external connector which provides for electrical connections for the level sensors, a common ground for the sensors and the fuel pump. This connector is wired to three push fit connectors on the underside of the flange. A quick release connector provides for the connection of the fuel feed pipe and breather.

The fuel pump module is mounted on a bayonet fitting at the base of the fuel tank. The module locks into position by rotating the module clockwise into the bayonet. The module comprises the fuel pump, the RH jet pump, the pump inlet filter, a second fine mesh filter which mounts into the carrier and an over pressure valve (PRV). The pump module, fuel filter and level sensors are available as serviceable components, the individual assembly components are not available separately.

FUEL PUMP MODULE







The fuel pump module is attached to the base of the fuel tank by the bayonet fitting. The pump module flange has three electrical connectors; one for the fuel pump motor and one for each of the fuel level sensors. All are connected to the external electrical connector via the connectors on the underside of the fuel pump module flange.

The pump module has a maximum rated flow of 180 liters/hour (47.55 US gallons/hour) and an output pressure of 5.0 bar (72.5 lbf/in2).

The fuel pump is energized by the fuel pump relay which is located in the Battery Junction Box (BJB) and the fuel pump control module which is located in the left hand side of the luggage compartment. The relay and control module are controlled by the engine control module The relay is energized at all times when the ignition switch is in ignition position II.

A 60 micron fine mesh, pump inlet filter is attached to the pump inlet port at the bottom of the pump. The filter is located vertically at the side of the pump to ensure that a portion of the filter is off the base of the swirl pot to prevent premature blocking of the filter.

A second, serviceable fine mesh filter is located in-line. This provides additional filtration to the fuel before it is passed to the fuel rail. The filter has an electrical connection which is attached to ground to prevent electrostatic build-up.

FUEL LEVEL SENSORS

Left Hand Fuel Level Sensor







Two fuel level sensors are installed in either side of the saddle tank. One is mounted on the fuel pump module, the other is mounted on a separate bracket in the other side of the fuel tank. The sensors are a Magnetic Passive Position Sensor (MAPPS) which provide a variable resistance to ground for the output from the fuel gage. The sensor is sealed from the fuel preventing contamination of the contacts, increasing reliability. The front and rear fuel level sensors are connected to the external electrical connector on the flange via the connectors on the underside of the fuel pump module flange.

The sensor comprises a series of 51 film resistors mounted in an arc on a ceramic surface. The resistors are wired in series with individual contacts. A soft magnetic foil with 51 flexible contacts is mounted a small distance above the film resistors. A magnet, located below the ceramic surface, is attached to the sender unit float arm. As the float arm moves, the magnet follows the same arc as the film resistors. The magnet pulls the flexible contacts onto the opposite film resistor contacts forming an electrical circuit.

Sensor Operating Principle







The film resistors are arranged in a linear arc with resistance ranging from 51.2 to 992.11 Ohms. The electrical output signal is output proportional to the amount of fuel in the tank and the position of the float arm. The measured resistance is processed by the instrument cluster to implement an anti-slosh function. This monitors the signal and updates the fuel gage pointer position at regular intervals, preventing constant pointer movement caused by fuel movement in the tank due to cornering or braking.

A warning lamp is incorporated in the instrument cluster and illuminates when the fuel level is at or below 10 liters (2.64 US gallons).

The fuel level sender signal is converted into a CAN message by the instrument cluster as a direct interpretation of the fuel tank contents in liters. The ECM uses the CAN message to store additional OBD P Codes for misfire detection when the fuel level is below a predetermined capacity.

JET PUMPS
The fuel system incorporates two jet pumps. The LH jet pump is located on the fuel level sensor carrier on the LH side of the fuel tank. The RH jet pump is located in the swirl pot below the fuel pump. Both jet pumps operate on a venturi effect created by the fuel at pump output pressure passing through the jet pump. This draws additional fuel from the tank through ports in the jet pump body, delivering additional fuel to the swirl pot.

The jet pump is connected via a pipe from a three-way connection in the fuel pump. The LH jet pump collects fuel from the LH side of the tank and transfers it into the swirl pot, ensuring a constant supply of fuel to the pump. The jet pump has a jet nozzle of 0.5 mm diameter.

The RH jet pump operates at pump output pressure and delivers some of the fuel at pump pressure from the LH side of the tank. The jet pump has a jet nozzle of 0.5 mm diameter.

LIQUID VAPOR SEPARATOR (LVS)







The Liquid Vapor Separator (LVS) separates any liquid from the vapor and drains back into the tank via the Fuel Level Vent Valve (FLVV) which is located on the underside of the LVS.

A single Roll Over Valve (ROV) is located in the liquid vapor separator. The separator is attached to the upper half of the fuel tank and is connected via a pipe and T piece to the charcoal canister breather outlet and the tank vent breather outlet. The ROV contains a non-return valve which closes in the event of the vehicle overturning, preventing liquid fuel escaping from the tank via the breather pipe.

FUEL LEVEL VENT VALVE (FLVV)
The main purpose of the FLVV is to control the fill volume of the tank. During filling, vapor is passed via the FLVV to the LVS. The vapor then passes from the LVS to the vent connection via a corrugated tube. The vent connection is connected to the charcoal canister which stores the fuel vapor. During filling, when the tank reaches its full level, the FLVV closes and prevents fuel vapor passing through to the LVS. This causes the pressure in the tank to rise which in turn causes the pump filling nozzle to turn off.

FUEL FILTER
The fuel filter is located on a bracket on the LH side of the fuel tank. The bracket is secured by a single bolt.

FUEL FILLER PIPE ASSEMBLY







The fuel filler head is positioned at the rear of the vehicle, above the right hand rear wheel. The filler head is covered by a molded plastic cover which is electrically locked when the vehicle is locked. The filler cap is a conventional screw in type which is secured to the vehicle with a lanyard.

The filler head is a stainless steel fabrication which is secured to the vehicle body by a bracket.

Connections on the rear of the filler head allow for the connection of the fuel tank breather pipe from the fuel tank flange, the fuel filler pipe to the tank and the charcoal canister breather pipe.

The fuel tank breather pipe has a quick release fitting and connects to the breather pipe from the fuel tank flange.

The fuel filler pipe locates in a short flexible hose attached to the tank and is secured with worm drive clamps. The canister breather pipe is routed alongside the fuel filler pipe and attaches to the canister with a quick release coupling.

A fourth pipe is also routed alongside the fuel filler pipe and provides air ventilation for the charcoal canister. On all petrol vehicles, except NAS vehicles, the pipe is connected to the air pump port on the charcoal canister with a quick release coupling and connects to an insect trap at the fuel filler head. On NAS vehicles fitted with a DMTL pump, the pipe connects to the pump vent port and is also connected to a filter which is attached to the filler head.

FUEL LINES
The fuel lines are single piece construction from the fuel filter to the fuel rails in the engine compartment.