Principles of Operation (How Does It Work)

WARNING:
- DO NOT MODIFY THE SYSTEM CONFIGURATION OR COMPONENTS OR INSTALL NEW COMPONENTS WITH PARTS NOT SPECIALLY DESIGNED FOR USE WITH NATURAL GAS. FORD MOTOR COMPANY HAS SPECIALLY DESIGNED THE MATERIALS, COMPONENTS AND SYSTEM CONFIGURATION FOR THE 4.6L (2V) CROWN VICTORIA NATURAL GAS VEHICLE, AND EACH PARTICULAR SYSTEM IS PRECISELY CALIBRATED FOR EFFICIENT OPERATION. THE USE OF DIFFERENT PARTS OR MATERIALS CAN PRODUCE AN UNTESTED CONFIGURATION THAT COULD RESULT IN FIRE OR PERSONAL INJURY OR CAUSE ENGINE DAMAGE.
- IT IS IMPORTANT THAT YOUR NATURAL GAS VEHICLE BE CORRECTLY MAINTAINED BY FORD NATURAL GAS TRAINED PERSONNEL. IF A CONCERN OCCURS, IT IS IMPORTANT THAT CORRECTLY TRAINED PERSONNEL DIAGNOSE THE CAUSE. IF THE PROBLEM RELATES TO THE FUEL SYSTEM, CORRECT PART REPLACEMENT IS IMPERATIVE TO KEEP YOUR VEHICLE OPERATING AT NORMAL PERFORMANCE. NATURAL GAS COMPONENTS AND GASOLINE FUEL COMPONENTS ARE NOT INTERCHANGEABLE. IF YOUR VEHICLE IS NOT REPAIRED IN ACCORDANCE WITH NATURAL GAS-FUELED VEHICLE PROCEDURES, DAMAGE CAN OCCUR AND YOUR WARRANTY MAY BE INVALIDATED.

NOTE:
- All standard production components and Systems receive routine repairs under base warranty procedures.
- For diagnosis and testing of non-NGV related instrument cluster functions, refer to Conventional Cluster.

Fuel Level Indication System
The Natural Gas Vehicle (NGV) fuel level indication system consists of the following components:
- an NGV module
- a fuel tank pressure sensor
- two fuel tank temperature sensors (No.1 [upper] and No.2 [lower])
- a fuel gauge (located in the instrument cluster
- a low fuel level warning switch (located on the back of the instrument cluster)

Low Fuel Level Warning Switch
The low fuel level warning switch:
- is designed to reduce fuel gauge pointer fluctuation.
- provides a low fuel warning when the fuel gauge indicates approximately 1/16 full.

Natural Gas Vehicle (NGV) Module
The NGV module assembly:
- consists of a 60-pin module, a bracket, a marine cover and four marine cover retainers.
- houses the unique electronics required for natural gas fuel systems.
- is located on the center radiator support, behind the radiator grille.

The NGV module carries out the following functions:
- injector drivers: the NGV module accepts eight unmodified injector signals from the powertrain control module (PCM) and allows a peak-and-sustain current to flow through the injector solenoids.

NOTE: No injector calculations are carried out; the injector driver output is not determined by the NGV module.

- fuel gauge driver: the NGV module uses fuel tank temperature and fuel tank pressure inputs to calculate the density of the fuel; a look-up table is used to determine the output signal to the low fuel warning switch (through a combination of discreet resistors), which drives the fuel gauge located in the instrument cluster.
- power and ground supply: the NGV module supplies power to the instrument cluster components on circuit 231 (BK/YE) when the ignition switch is in the RUN and START positions. Ground for the fuel gauge, the low fuel level warning switch and the voltmeter is supplied on circuit 570 (BK/WH). circuit 231 (BK/YE) also supplies power to the following components in the instrument cluster:
- low fuel indicator
- CHECK ENGINE indicator (Malfunction Indicator Lamp [MIL])
- speedometer
- temperature gauge
- oil pressure gauge
- Anti-Lock Braking System (ABS) indicator
- Overdrive (OD) OFF indicator
- brake warning indicator
- AIR BAG warning indicator
- fail-safe cooling indicator

Fuel Tank Pressure Sensor
The fuel tank pressure sensor:
- contains integral solid state circuitry that outputs a voltage signal that is proportional to pressure.
- has an output that is linear from 0 kPa (0 psi) up to 27,579.03 kPa (4000 psi).
- is located in the upper tank vent box on the upper tank rack.

Fuel Tank Temperature Sensors
The fuel tank temperature sensors:
- change resistance in response to the temperature of the fuel in the fuel tank; as the surrounding temperature increases, the resistance decreases (the voltage signal also decreases).
- provides a signal to the NGV module that indicates the temperature of the fuel.
- are located next to the fuel tanks, one in the vent box at Fuel Tank No.1 (Fuel Tank Temperature Sensor No.1) and one below the vehicle at Fuel Tank No.4 (Fuel Tank Temperature Sensor No.2).

Diagnostic Instructions
The NGV module monitors the components and circuitry required for fuel indication during normal operation. If an error or concern is detected, the NGV module will store a Diagnostic Trouble Code (DTC) in memory. DTCs are retrieved from the NGV module using the diagnostic tool. If a concern exists with an instrument cluster component that is not related to the fuel indication system, refer to the symptom chart in Instrument Panel, Gauges and Warning Indicators for diagnosis of that component. DO NOT carry out NGV module diagnostics. The components monitored by the NGV module include:
- fuel tank temperature sensors
- fuel tank pressure sensor
- fuel gauge
- circuitry

Fuel gauge accuracy can be affected by certain conditions. These conditions will cause abnormal fuel gauge movement, possibly causing unnecessary diagnostics. Make sure the following conditions do not exist before continuing with fuel indication system diagnostics:
A. Fast filling
- After fast filling a vehicle, the fuel gauge reading can drop as much as 1/16 of a tank. This is caused by the rapid expansion and compression of the fuel during fast fills. This is considered normal gauge movement.
- Fast filling with the ignition switch in the RUN position can cause the NGV module to store DTCs in error. With the ignition switch in the RUN position, the NGV module is monitoring the sensors. During fast fill situations, the tank temperature drops to extremely low temperatures; this may cause the fuel tank temperature sensors to drop below their operating temperature range, causing the NGV module to store a DTC. When fast filling is complete, the fuel tank temperature sensors will return to normal operation after it reaches normal operating temperature range. However, the DTC will still be stored.
- Fast filling with the ignition switch in the RUN position will cause the fuel gauge to move very slowly toward Full; this is eliminated when the vehicle is filled with the ignition switch in the OFF position.

B. Fuel system leaks.
- Fuel leaks can cause inaccurate fuel gauge readings. Depending on the size of the leak, the fuel gauge may not be able to maintain an accurate reading if the fuel leak exceeds the low fuel level warning switch and NGV module's ability to update the fuel gauge. This creates a possibility for the fuel gauge to display a fuel level when the fuel tanks are empty. Before diagnosing this type of concern, make sure the fuel system is not leaking.

NOTE: Refer to Fuel Delivery and Air Induction for the Fuel System Leak Test.

- After repair of a fuel system that has been drained, the fuel gauge will display Empty during the initial key-on of the ignition switch since there is no pressure in the fuel lines. After 4-5 key-ons, the fuel gauge will display the appropriate reading.

C. Erratic instrument cluster operation
- The NGV module has an internal on-board diagnostic mode which is not used with diagnostic tool diagnostic procedures. However, if the ignition switch is cycled from OFF to RUN four times and left in the RUN position without the engine being started, the NGV module will cause the instrument cluster to react erratically. Warning indicators will remain illuminated and the voltage and fuel gauge pointers will move sporadically. If this concern exists, start the engine. If the concern is still present, continue with NGV module diagnostics.