Fuel Rail: Description and Operation

NATURAL GAS FUEL SYSTEM

Fuel Rail

Fuel Rail Components:

The fuel rail (Figure 78) distributes low pressure fuel from the chassis supply line to each fuel injector. Fuel pressure at the top of each fuel injector is maintained within 1% of the other fuel injectors at all times; this is done with nearly symmetric flow paths. The fuel rail is also designed to have minimal flow restriction by increasing the cross-sectional flow area and reducing the flow path length. The fuel rail contains several other Parts In Assembly (PIA) components that perform crucial functions. These include:
- Injection pressure sensor which measures the pressure of the fuel near the fuel injectors. This signal is used by the PCM to adjust the fuel injector pulse width and meter fuel to each engine combustion cylinder.
- Engine fuel temperature sensor which measures the pressure of the fuel near the fuel injectors. This signal is used by the PCM to adjust the fuel injector pulse width and meter fuel to each engine combustion cylinder.
- Low pressure solenoid shut-off valve which isolates the fuel rail from the upstream fuel system when the engine is OFF. This minimizes the amount of fuel available to flow through the fuel injectors when the engine is off or leak from a damaged fuel rail during and after a crash. The valve is controlled by the PCM fuel shut-off valve circuit and contains an inertia switch. The valve is only on for one second after a key-on or whenever CKP signals are being received by the PCM.
- schrader/service valve (if equipped) provides a service port to the low pressure fuel system. This valve is needed to relieve the pressure in the system before and during service. This valve could also be used to monitor the pressure near the injectors during diagnostic procedures.

Fuel Rail Shut-Off Valve

Fuel Rail Shut-Off Valve:

The fuel rail shut-off valve (Figure 86) is a normally closed solenoid actuated valve that opens when (along with all of the tank valves) Pin 80 is grounded by the PCM. The valve isolates the fuel injectors from fuel line pressure when the engine is off. Nominal resistance of the coil is 11 ohms. The fuel rail shut-off valve is wired in parallel with the four tank valves.

Fuel Rail Valve Circuit Operation
When the key is turned to the ON position, the power relay is turned on. The power relay provides power to the PCM and the control side of the fuel shut off valve relay. The relay provides voltage to the fuel rail valve. If the ignition switch is not turned to the START position, the PCM will shut off the fuel rail valve after one second. The PCM will open the valve (along with the four tank valves) to provide fuel while cranking. The valve will remain open when the engine is running unless the inertia fuel shut-off switch is "tripped."