Fuel Management: Notes

Fuel Tank:  The fuel tank is made of high density polyethylene (reduced weight) which is manufactured to meet safety requirements.

A mid-chassis mounted "saddle" type tank is used providing a tunnel for the driveshaft but creates two separate lower chambers.

A syphon jet is required with this type of tank to transfer fuel from the left side, linked to the fuel return line. As fuel moves through the return, the syphon jet creates a low pressure (suction) to pick up fuel from the left side of the tank and transfer it to the right side at the fuel pick up.

The fuel tank capacity is 55 liters (14.5 gallons). This includes a rerve capacity of 8 liters (2 gal.). 

The E85 fuel tank design represents the next step in reducing the potential evaporative emissions. This design reduces the number of external connections and openings by increasing the amount of "in tank" or integral components  . The fuel system is divided into two subsystems: fuel supply and fuel ventilation (evaporative contaiment and control - refer to EMISSIONS MANAGEMENT  section).

MS45 Fuel Supply: 

When the fuel pump is energized, it supplies fuel from the pickup area in the baffle chamber through the fuel filter to the fuel pressure regulator. The fuel supply pressure is controlled by the 3.5 Bar fuel pressure regulator  (integrated in the fuel filter assembly). The regulator is influenced by internal fuel pressure and not intake manifold vacuum. The fuel exits the fuel pressure regulator supplying the fuel rail and the injectors. The fuel rail distributes an even supply of fuel to all of the injectors, and also serves as a volume reservoir.

The fuel is supplied through a Non Return Fuel Rail System. The fuel return line is located on the filter/regulator assembly which directs the unused fuel back through the fuel tank. The fuel tank hydrocarbons are reduced by returning the fuel from this point (lower temperatures) instead of from the fuel rail.

As fuel moves through the return, the syphon jet creates a low pressure (suction) to pick up fuel from the left side of the tank and transfer it to the right side at the fuel pick up. A second syphon jet is mounted through the baffle chamber to draw as much fuel as possible from the right side of the tank into the baffle chamber (critical for low fuel or reserve situations).

Fuel Pump:  The electric fuel pump supplies constant fuel volume to the injection system. This system uses a single submersible (in the fuel tank) pump. The inlet is protected by a mesh screen.

When the fuel pump is powered, the armature will rotate the impeller disc creating low pressure at the inlet. The fuel will be drawn into the inlet and passed through the fuel pump housing (around the armature). The fuel lubricates and cools the intervals of the pump motor.

The fuel will exit through a non-return check valve to supply the injection system. The non-return check valve is opened by fuel exiting the pump and will close when the pump is deactivated. This maintains a "prime" of fuel in the filter, lines, hoses and fuel rail.

The pump contains an internal overpressure relief valve that will open (reducing roller cell pressure) if there is a restriction in the fuel supply hardware.

Fuel Supply Components:  The fuel is transferred from the fuel pump to the fuel filter. The fuel filter "traps" contaminants before they reach the fuel injectors and should be replaced at the specified interval. The large filter size also serves as a volume reservoir (dampening fuel pump pulsations).

Fuel Pressure Regulator:  The Fuel Pressure Regulator maintains a constant pressure for the fuel injectors. The fuel pressure is set to 3.5 bar  by internal spring tension on the restriction valve. The fuel pressure regulator is not influenced by vacuum.

The ECM determines the fuel quantity compensation for manifold vacuum changes. This is based on throttle position, HFM and load for precise compensation.

When the restriction valve opens, unused fuel returns from the regulator/filter assembly back through the fuel tank to the left side syphon jet.

Siemens Fuel Injectors:  The Fuel Injectors are electronically controlled solenoid valves that provide precise metered and atomized fuel into the engine intake ports. The Fuel Injector Valve consists of:

Fuel is supplied from the fuel rail to the injector body. The fuel is channeled through the injector body to the needle valve and seat at the tip of the injector. Without electrical current, the needle valve is sprung closed against the seat.

The Fuel Injectors receive voltage from the Fuel Injector Relay. The ECM activates current flow through the injector solenoid creating a magnetic field that pulls the needle "up" off of its seat. The pressurized fuel flows through the tip of the injector that is fitted with a directional angle "plate" with dual outlets. This "fans out" the spray into an angled patterns which helps to atomize the fuel. When the ECM deactivates current flow, the needle valve is sprung closed against the seat and fuel flow through the injector is stopped. The lower portion of the injector body is jacketed in metal.

The length of time that the ECM activates the Fuel Injectors is very brief, the duration is in milli-seconds (ms). This affects the mount of fuel volume flowing through the Fuel Injectors. The ECM will vary the length of time (ms) to regulate the air/fuel ratio (mixture).

A Fuel Injector is faulty (mechanical or electrical), it can produce the following complaints:

• Malfunction Indicator Light
• Excessive Tailpipe smoke (leaking)
• Engine Hydrolock (leaking)
• Misfire/Rough Idle (Leaking or Blocked)
• Long Crank Time (Leaking)
• Oxygen Sensor/Mixture/Injector Related Fault Code

Crankshaft Position/RPM Sensor (Hall Effect):  This sensor provides the crankshaft position and engine speed (RPM) signal to the ECM for fuel pump and Injector operation.

A Hall sensor is mounted on the left side at the rear of the engine block. The impulse wheel is mounted on the crankshaft inside the crankcase, at the rear main bearing support. The impulse wheel contains 58 teeth with a gap of two missing teeth.

The Hall sensor is supplied with voltage from the ECM. A digital square wave signal is produced by the sensor as the teeth of the impulse wheel pass by. The "gap" allows the ECM to establish crankshaft position.

The crankshaft position sensor is monitored as part of OBD II requirements for Misfire Detection. If this input is faulty, the ECM will operate the engine (limited driveability) from the Camshaft Sensor input. A fault with this input will produce the following complaints:

• Hard Starting/Long Crank Time
• "Malfunction Indicator Light"
• Driveability/Misfire/Engine Stalling