Fuel Delivery: Notes

Natural Gas (NG) fuel system consists of fuel tank(s), fuel shutoff valve assemblies, fuel supply lines, fuel filter, manual shutoff valve(s), service (Schrader) valve, fuel injection supply manifold and fuel pressure regulator. The following list of components and their specific operation corresponds to numbers in illustration. See Fig 1.

1. The Crankshaft Position (CKP) sensor is used to signal PCM that engine is either cranking or running.
2. The fuel shutoff valve logic is defined in Fuel System control strategy and is executed in PCM. PCM will ground fuel pump relay for one second during Key On Engine Off (KOEO). During cranking, fuel pump relay is grounded as long as PCM receives a signal from CKP.
3. The fuel pump relay has a primary and a secondary circuit. The primary side is controlled by PCM and secondary side provides battery voltage (B+) to fuel shutoff valve circuit when relay is energized.
4. The Inertia Fuel Shutoff (IFS) switch is used to de-energize fuel delivery secondary circuit in the event of a collision. IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision). For additional IFS information, see INERTIA FUEL SHUTOFF SWITCH (ALL FUEL SYSTEMS) .
5. The fuel injector is used to meter natural gas to each combustion cylinder. Although NG fuel injector appears very similar to some gasoline fuel injectors, it is unique. Flow capacity of this fuel injector is 6-12 times as large as various gasoline fuel injectors. See Fig 2. For additional NG fuel injector information, see NG FUEL INJECTORS  under FUEL CONTROL.
6. The fuel tank shutoff solenoid valve is located in fuel tank. The solenoid valves are on the same circuit as fuel pump and utilize the same Inertia Fuel Shutoff (IFS) switch as gasoline models. For additional fuel tank shutoff solenoid valve information, see FUEL TANK SHUTOFF VALVE .
7. The high pressure fuel filter is used to protect engine fuel system components. A natural gas coalescing and particulate filter is located on high pressure side of fuel system just prior to fuel pressure regulator. Filter is part of regulator assembly. Filter can be disassembled to service the element. Drain plug on bottom of filter housing can be removed to drain any accumulated water.
8. Fuel pressure regulator used on NG vehicles is a single-staged pressure reducing regulator which expands natural gas from storage pressures of 200-3000 psi (1379-20,685 kPa) to engine fuel pressures of 105-125 psi (724-862 kPa). For additional NG fuel pressure regulator information, see NG FUEL PRESSURE REGULATOR .
9. The fuel rail shutoff valve is a normally closed solenoid actuated valve that opens when terminal No. 80 is grounded by PCM. The valve isolates fuel injectors from fuel line pressure when engine is not operating. The fuel rail shutoff valve is wired in parallel with fuel tank shutoff solenoid valves. For additional fuel rail shutoff valve information, see FUEL RAIL SHUTOFF VALVE .