Ford F150 Pickup. Instruction — part 1633

tripped open when the internal steel ball breaks loose of the switch magnet. See Fig. 40 . Once loose, the steel
ball rolls up a conical ramp and makes contact with the target plate which creates an open in the electrical
circuit to electric fuel pump. If the electrical circuit is opened, it is not possible to restart the vehicle until the
switch is reset. A reset button is located on top of IFS switch assembly.

Fig. 40: Identifying Inertia Fuel Shutoff Switch
Courtesy of FORD MOTOR CO.

FUEL CONTROL

Fuel Injectors

The fuel injector is a solenoid-operated valve that meters fuel flow to the engine. See Fig. 41 . The fuel injector
is opened and closed a constant number of times per crankshaft revolution. The amount of fuel is controlled by
the length of time the fuel injector is held open.

The fuel injector is normally closed and is operated by 12 volt VPWR from the electronic engine control power

CAUTION: DO NOT apply battery voltage directly to fuel injector electrical connector

terminals, internal damage to fuel injector may occur.

NOTE:

Fuel injectors are deposit resistant and must not be cleaned.

2003 Ford Pickup F150

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline

relay. The ground signal is controlled by the PCM.

The injector is the Deposit Resistant Injection (DRI) type and does not have to be cleaned. However, it can be
flow checked and, if found outside of specification, the fuel injector should be replaced.

Fig. 41: Cross-Sectional View Of Fuel Injector Assembly
Courtesy of FORD MOTOR CO.

FUEL SYSTEMS (NATURAL GAS)

CAUTION: DO NOT apply battery positive voltage (B+) directly to the fuel injector

electrical connector terminals. The solenoids may be damaged internally
in a matter of seconds.

2003 Ford Pickup F150

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline

FUEL DELIVERY

Natural Gas (NG) fuel system consists of fuel tank(s), fuel shutoff valve assemblies, fuel supply lines, fuel
filter, instruction 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. 42 .

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. 43 . 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 .

2003 Ford Pickup F150

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline

Fig. 42: Identifying Natural Gas Fuel System Components & Circuits
Courtesy of FORD MOTOR CO.

Fig. 43: Identifying Natural Gas Fuel Delivery Components
Courtesy of FORD MOTOR CO.

2003 Ford Pickup F150

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline