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Home >> Ford >> 2000 >> Taurus LX, 3.0 2, AX4N >> Repair and Diagnosis >> External Pages >> Different car >> Section 1836 (Engine Controls Self-Diagnostics - EEC-V - CNG & Gasoline - System Tests Ff - Kc) >> Test HB: Natural Gas Fuel Delivery System >> Diagnostic Aids

Diagnostic Aids

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Perform this test when directed by QUICK TEST or if directed by other test procedures. This test is used to diagnose:

NOTE: Fuel rail solenoid shutoff valve is also referred to as low pressure solenoid shutoff valve. Fuel tank solenoid shutoff valve is also referred to as fuel tank solenoid valve.

  1. 1) Check System Integrity

    Turn ignition switch to ON position for 5 seconds. Turn ignition switch to OFF position. Inspect fuel system for leaks, damaged or kinked hoses. See Fig 1 or Fig 2 . Inspect wiring harness for damage or loose connectors. Ensure the following conditions are present:
    • Fuel Filter Element Is Okay
    • Inertia Fuel Shutoff (IFS) Is Set
    • Battery Is Fully Charged
    • Fuel System Fuses Are Okay

    Repair problems as necessary. If vehicle exhibits poor fuel economy, perform appropriate FUEL SYSTEM PRESSURE RELEASE procedure under FUEL SYSTEM VENTING in REMOVAL, OVERHAUL & INSTALLATION - CARS & TRUCKS - BI-FUEL & CNG article. If fuel smell is present, go to step  16). If no faults are found or for all other symptoms, go to next step.

    Fig 1: Identifying CNG Fuel System Components (Crown Victoria)
    G98J01004Courtesy of FORD MOTOR CO
    Fig 2: Identifying CNG Fuel System Components (Econoline & Pickup)
    G98C01005Courtesy of FORD MOTOR CO

  2. 2) Check Fuel Tank Pressure

    Turn ignition switch to OFF position. Install fuel tank venting tool supplied in Kit (134-00114) to vehicle fueling connector. Open by-pass valve, located on fill valve. Turn ignition switch to ON position. Record fuel tank pressure. If pressure is more than 500 psi (3448 kPa), turn ignition switch to OFF position. Close by-pass valve. Remove fuel tank venting tool and go to step  5). If fuel pressure is 500 psi (3448 kPa) or less, turn ignition switch to OFF position. Check fuel level. Fill tank if necessary. If fuel level is okay, check for power at tank solenoid valve. Go to next step.
    3. NOTE: When energized by scan tool, FSV PWR circuit to fuel tank solenoid shutoff valve will remain on for only 7 seconds.

  3. 3) Check FSV PWR & GND Circuits To Fuel Tank Solenoid Shutoff Valve
    Connect scan tool to Data Link Connector (DLC). Turn ignition switch to ON position. Using scan tool, enter OUTPUT TEST MODE. Select ALL ON. Using a DVOM, measure voltage between fuel tank solenoid shutoff valve harness connector FSV PWR and GND circuit terminals. See WIRING DIAGRAMS article. Fuel tank solenoid shutoff valve is located on fuel tank (one per tank). If voltage is 10.5 volts or less, go to next step. If voltage is more than 10.5 volts, perform appropriate UNABLE TO VENT FUEL TANKS OR FUEL LINES diagnostic procedures under FUEL SYSTEM (NATURAL GAS VEHICLES) in SYSTEM & COMPONENT TESTING - EEC-V - BI-FUEL & CNG article to check for faulty fuel tank solenoid shutoff valve. Replace as necessary.

  4. 4) Check For Open GND Circuit To Fuel Tank Solenoid Shutoff Valve

    Using a DVOM, measure resistance between negative battery terminal and fuel tank solenoid shutoff valve harness connector GND circuit terminal. If resistance is less than 5 ohms, repair open in FSV PWR circuit. Verify symptom is no longer present. If resistance is 5 ohms or more, repair open in GND circuit to tank solenoid shutoff valve. Verify symptom is no longer present.
    5. WARNING: Fuel system remains under high pressure even when engine is not running. To avoid injury, release fuel pressure before disconnecting any fuel system hose or component. See appropriate FUEL SYSTEM PRESSURE RELEASE procedure under FUEL SYSTEM VENTING in REMOVAL, OVERHAUL & INSTALLATION - CARS & TRUCKS - BI-FUEL & CNG article.

  5. 5) Check Fuel Pressure
    Connect fuel pressure gauge supplied in Kit (134-00114) to Schrader valve located on fuel rail. Release fuel pressure in fuel injection rail and fuel supply lines. See appropriate FUEL SYSTEM PRESSURE RELEASE procedure under FUEL SYSTEM VENTING in REMOVAL, OVERHAUL & INSTALLATION - CARS & TRUCKS - BI-FUEL & CNG article. Turn ignition switch to ON position or start engine (if possible). Turn ignition switch to OFF position. Wait 2 minutes and check fuel pressure. If fuel pressure is 80-120 psi (552-827 kPa), go to next step. If fuel pressure is not 80-120 psi (552-827 kPa), replace fuel pressure regulator. Verify symptom is no longer present.

  6. 6) Check Fuel Rail Pressure Sensor Accuracy

    Turn ignition switch to OFF position. Connect fuel pressure gauge with vent hose supplied in Kit (134-00114) to Schrader valve located on fuel rail. Turn ignition switch to ON position. Using scan tool, select FRP PID from PID/DATA MONITOR & RECORD menu. Record FRP PID pressure reading. Observe and record fuel pressure reading at fuel pressure gauge. Turn ignition switch to OFF position. Slowly open shutoff valve on fuel pressure gauge and bleed fuel pressure down to 50-70 psi (345-483 kPa). Remove fuel pump relay. Turn ignition switch to ON position. Using scan tool, record FRP PID pressure reading. Observe and record fuel pressure reading at fuel pressure gauge.

    Turn ignition switch to OFF position. Compare fuel pressure readings taken with fuel pump relay installed and removed. If FRP PID value is not consistent and within 10 psi (69 kPa) of fuel pressure reading at fuel pressure gauge, go to next step. If FRP PID value is consistent and within 10 psi (69 kPa) of fuel pressure reading at fuel pressure gauge, for no-start vehicles go to step  10), for all others diagnose by symptom. See SYMPTOMS in TROUBLE SHOOTING - NO CODES - EEC-V - CNG & GASOLINE.

  7. 7) Verify Fuel Rail Solenoid Shutoff Valve Opens

    Ensure fuel pressure gauge with vent hose supplied in Kit (134-00114) are connected to Schrader valve located on fuel rail. Connect scan tool to Data Link Connector (DLC). Turn ignition switch to ON position. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE under ADDITIONAL SYSTEM FUNCTIONS. Select ALL ON. Start and stop tests several times by toggling START/STOP button on scan tool. An audible click should be heard or felt from fuel rail solenoid shutoff valve when cycled by scan tool. Turn ignition switch to OFF position. If fuel rail solenoid shutoff valve did not operate as specified, go to next step. If fuel rail solenoid shutoff valve operated correctly, replace FRP sensor. Verify symptom is no longer present.
    8. NOTE: When energized by scan tool, FSV PWR circuit to fuel rail solenoid shutoff valve will remain on for only 7 seconds.

  8. 8) Check FSV PWR & GND Circuits To Fuel Rail Solenoid Shutoff Valve
    Turn ignition switch to ON position. Using scan tool, again access OUTPUT TEST MODE. See OUTPUT TEST MODE under ADDITIONAL SYSTEM FUNCTIONS. Select ALL ON and press START. Using a DVOM, measure voltage between fuel rail solenoid shutoff solenoid harness connector FSV PWR circuit and GND circuit terminals. See WIRING DIAGRAMS article. If voltage is 10.5 volts or less, go to next step. If voltage is more than 10.5 volts, replace fuel rail solenoid shutoff valve. Verify symptom is no longer present.

  9. 9) Check For Open GND Circuit To Fuel Rail Solenoid Shutoff Valve

    Using a DVOM, measure resistance between battery negative terminal and fuel rail solenoid shutoff valve harness connector GND circuit terminal. See WIRING DIAGRAMS article. If resistance is less than 5 ohms, repair open in FSV PWR circuit. If resistance is 5 ohms or more, repair open in GND circuit. Verify symptom is no longer present.

  10. 10) Verify Fuel Rail Solenoid Shutoff Valve Seals

    Ensure fuel pressure gauge with vent hose supplied in Kit (134-00114) are connected to Schrader valve located on fuel rail. Release fuel pressure in fuel injector rail and supply lines. See appropriate FUEL SYSTEM PRESSURE RELEASE procedure under FUEL SYSTEM VENTING in REMOVAL, OVERHAUL & INSTALLATION - CARS & TRUCKS - BI-FUEL & CNG article. Disconnect fuel rail solenoid shutoff valve harness connector at fuel rail. Crank engine for 3 seconds (DO NOT start engine). Turn ignition switch to OFF position and wait 2 minutes. Using scan tool, select FRP PID from PID/DATA MONITOR & RECORD menu.. Turn ignition switch to ON position and record FRP PID value. If FRP PID value is less than 10 psi (70 kPa), go to next step. If FRP PID value is 10 psi (70 kPa) or more, replace fuel rail solenoid shutoff valve. Verify symptom is no longer present.

  11. 11) Verify Fuel Rail Solenoid Shutoff Valve Partially Opens

    Turn ignition switch to OFF position. Ensure fuel pressure gauge with vent hose supplied in Kit (134-00114) are connected to Schrader valve located on fuel rail. Release fuel pressure in fuel injector rail and supply lines. See appropriate FUEL SYSTEM PRESSURE RELEASE procedure under FUEL SYSTEM VENTING in REMOVAL, OVERHAUL & INSTALLATION - CARS & TRUCKS - BI-FUEL & CNG article. Ensure fuel rail solenoid shutoff valve harness connector is disconnected. Turn ignition switch to ON position, engine off. Turn ignition switch to OFF position. Reconnect fuel rail solenoid shutoff valve harness connector. Turn ignition switch to ON position, engine off. Using scan tool, select FRP PID and record FRP PID value. Record fuel rail pressure reading shown on fuel pressure gauge. Compare FRP PID value to fuel rail pressure reading. If FRP PID value is within 10 psi (70 kPa) of fuel pressure reading at Schrader valve on fuel rail, go to next step. If FRP PID value is not within 10 psi (70 kPa) of fuel pressure reading at Schrader valve on fuel rail, replace fuel rail solenoid shutoff valve. Verify symptom is no longer present.

  12. 12) Verify Fuel Rail Solenoid Shutoff Valve Fully Opens

    Ensure fuel pressure gauge with vent hose supplied in Kit (134-00114) are connected to Schrader valve located on fuel rail. Release fuel pressure in fuel injector rail and supply lines. See appropriate FUEL SYSTEM PRESSURE RELEASE procedure under FUEL SYSTEM VENTING in REMOVAL, OVERHAUL & INSTALLATION - CARS & TRUCKS - BI-FUEL & CNG article. Disconnect fuel rail solenoid shutoff valve harness connector. Turn ignition switch to ON position, engine off. Turn ignition switch to OFF position. Reconnect fuel rail solenoid shutoff valve harness connector. Turn ignition switch to ON position and immediately start engine. Increase engine speed to 2500 RPM while monitoring FRP PID value. Record fuel rail pressure reading shown on fuel pressure gauge. Compare FRP PID value to fuel rail pressure reading. If FRP PID value is within 10 psi (70 kPa) of fuel pressure at Schrader valve on fuel rail, go to next step. If FRP PID value is not within 10 psi (70 kPa) of fuel pressure at Schrader valve on fuel rail, replace fuel rail solenoid shutoff valve. Verify symptom is no longer present.

  13. 13) Check Fuel Pressure With Engine Running

    Start engine and allow to idle. Using scan tool, select FRP PID from PID/DATA MONITOR & RECORD menu. Record FRP PID value. Increase engine speed to 2500 RPM. Again, record FRP PID value. If FRP PID value at idle is 80-120 (552-827 kPa) and more than 80 psi (552 kPa) with engine speed at 2500 RPM, turn ignition switch to OFF position and go to next step. If FRP PID value is not as specified, check for plugged fuel lines. Repair as necessary and retest. If fuel lines are okay, replace fuel pressure regulator. Verify symptom is no longer present.

  14. 14) Check Fuel Pressure Regulator Thermostat

    Start engine and allow to idle. Allow engine to reach normal operating temperature. Using a thermometer or temperature probe, measure temperature at fuel pressure regulator coolant bowl or coolant outlet. If temperature is 59-140°F (15-60°C), turn ignition switch to OFF position and go to next step. If temperature is less than 59°F (15°C), check coolant lines and coolant system. Repair as necessary and retest. If coolant lines and system are okay, replace fuel pressure regulator. If temperature is more than 140°F (60°C), replace fuel pressure regulator. Verify symptom is no longer present.

  15. 15) Check Fuel Injector Flow

    Turn ignition switch to ON position. Using scan tool, select FRP PID from PID/DATA MONITOR & RECORD menu. Record initial FRP PID value. Connect Fuel Injector Tester (164-R3795) to suspect fuel injector. Using scan tool, select pulse width of 200 milliseconds and activate fuel injector tester. Record final FRP PID value. Compare initial FRP PID value to final FRP PID value. Repeat procedure for remaining fuel injectors. Initial FRP PID value should be 35-50 psi (241-345 kPa) and each injector FRP PID value should be within 3 psi (20 kPa) of each other. If fuel injectors are not within specification, replace faulty fuel injector(s). If fuel injectors are within specification, no problem is indicated at this time. If symptom still exists, diagnose by symptom. See SYMPTOMS under TROUBLE SHOOTING - NO CODES - EEC-V - CNG & GASOLINE article.
    16. NOTE: If vehicle has sat for several hours with engine off, a slight CNG smell may be detected around the intake manifold area. This is a normal condition.

  16. 16) Check For Fuel Leak
    Turn ignition switch to OFF position. Inspect fuel system for obvious signs of fuel leaking. If fuel system looks okay, release fuel system pressure. Install fuel pressure gauge supplied in Kit (134-00114) to Schrader valve located on fuel rail. Turn ignition switch to ON position, engine off. Fuel pressure should be more than 85 psi (586 kPa). Using Natural Gas Sniffer (134-00114) or covering fuel system components, lines and joints with soapy water solution, check for fuel leaks. If no bubbles develop and/or sniffer does not detect a leak, fuel leaks cannot be found and testing is complete. If bubbles develop or sniffer senses a leak, isolate fault and repair as necessary.

  17. 17) DTC P1180 & P1181: Check Fuel Pressure

    Inspect fuel lines, fuel regulator and fuel filter for leaks and restrictions. Repair as necessary. If no leaks or restrictions are found, go to next step.

  18. 18) Check Fuel Tank Pressure

    Connect scan tool to Data Link Connector (DLC). Place gearshift lever in "P" position. Start engine and allow to idle. Using scan tool, select TANKPR PID from CNG menu. Record TANKPR PID value. Using scan tool, select FRP PID from PID/DATA MONITOR & RECORD menu. Record FRP PID value. Locate approximate TANKPR PID value and determine PCM inferred pressure. See PCM INFERRED PRESSURE SPECIFICATIONS  table. If PCM inferred pressure is within 22 psi (plus or minus) of FRP PID value, no problem is indicated at this time. Service any other DTCs that are present. If PCM inferred pressure is not within 22 psi (plus or minus) of FRP PID value, go to next step for DTC P1180, or replace fuel pressure regulator for DTC P1181.
    PCM INFERRED PRESSURE SPECIFICATIONS

    TANKPR PID Value - psi (kPa) PCM Inferred Pressure - psi (kPa)
    290 (2000) 109 (752)
    435 (3000) 108.4 (747)
    580 (4000) 106.9 (737)
    725 (5000) 106.5 (734)
    870 (6000) 106 (731)
    1015 (7000) 105.6 (728)
    1160 (8000) 105 (724)
    1305 (9000) 104.5 (721)
    1450 (10,000) 103.4 (713)
    1595 (11,000) 103 (710)
    1740 (12,000) 102.5 (707)
    1885 (13,000) 102.3 (705)
    2030 (14,000) 101.8 (702)
    2321 (16,000) 100.8 (695)
    2465 (17,000) 99.8 (688)
    2611 (18,000) 99.3 (685)
    2755 (19,000) 99 (683)
    2901 (20,000) 98.5 (679)
    3045 (21,000) 97.5 (672)
    3191 (22,000) 97.3 (671)
    3335 (23,000) 96.3 (664)
    3481 (24,000) 96 (662)
    3770 (26,000) 96 (662)
    4060 (28,000) 95.5 (658)
    4350 (30,000) 94 (648)

  19. 19) Check Fuel Filter For Water Or Other Contamination

    Disassemble fuel filter and check for water or any other contamination. If contamination is present, clean contaminants from filter housing and replace filter. If no contamination is present, go to next step.

  20. 20) Check Fuel Line For Restriction

    Visually inspect fuel lines for restrictions and leakage. Repair as necessary. If fuel lines are okay, replace fuel pressure regulator.
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