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Home >> Mazda >> 1999 >> B2500 SX, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 4 (Engine Controls - Self-Diagnostics - EEC-V - 6.8L (99S E Series & 99S F350 To F550)) >> System Tests >> 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 off. Inspect fuel system for leaks, damage or kinked hoses. See Fig 1 or Fig 2 . Inspect wiring harness for damage or loose connectors. Ensure the following conditions are present:
    • Battery is fully charged and fuses are okay.
    • Fuel filter element is okay.

    If vehicle does not start, ensure vehicle has fuel in tank and Inertia Fuel Shutoff (IFS) switch is set correctly. Repair as necessary and verify symptom no longer exists. If fuel smell is present, go to step  16. If no faults are found, go to next step.

    Fig 1: Identifying NG Fuel System Components (Crown Victoria)
    G98J01004Courtesy of FORD MOTOR CO
    Fig 2: Identifying NG Fuel System Components (Econoline, F150 & F250)
    G98C01005Courtesy of FORD MOTOR CO

  2. 2) Check Fuel Tank Pressure

    Turn ignition off. Install fuel tank venting tool (supplied in Kit 134-00114) to vehicle fueling connector. Open by-pass on fill valve. Turn ignition on. Record fuel tank pressure reading. If pressure reading is more than 500 psi (3447 kPa), turn ignition off. Close by-pass on fill valve. Remove fuel tank venting tool and go to step  5). If fuel pressure is 500 psi (3447 kPa) or less, turn ignition off. Close by-pass on fill valve. Remove fuel tank venting tool and go to next step.

  3. 3) Check Voltage At Fuel Tank Solenoid Shutoff Valve

    Turn ignition on. Using scan tool, enter OUTPUT TEST MODE. Turn all outputs on. Measure voltage between GROUND terminal and POWER CIRCUIT terminal at fuel tank solenoid shutoff valve wiring harness connector. 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, check for faulty fuel tank solenoid shutoff valve. Replace as necessary.

  4. 4) Check VPWR Circuit Between Solenoid & Battery

    With scan tool still in OUTPUT TEST MODE. Turn all outputs on. Measure voltage between negative battery terminal and PWR terminal at fuel tank solenoid shutoff valve wiring harness connector. If voltage is 10.5 volts or less, repair open in PWR circuit. If voltage is more than 10.5 volts, repair open in ground circuit to tank solenoid shutoff valve. Verify symptom is no longer present.
    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 REMOVAL, OVERHAUL & INSTALLATION article.

  5. 5) Check Fuel Pressure

    Connect fuel pressure gauge to Schrader valve. Release fuel pressure in fuel injection rail back to fuel tanks. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Turn ignition on or start engine. Turn ignition off. 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.

  6. 6) Verify Fuel Rail Pressure (FRP) Sensor Accuracy

    Turn ignition off. Connect fuel pressure gauge with vent hose to Schrader valve on fuel rail. Turn ignition on. Using scan tool, select FRP PID from PID/DATA monitor menu. Note FRP PID pressure reading. Observe fuel gauge and note fuel pressure. Turn ignition off. 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 on. Note FRP PID pressure reading on scan tool. Note fuel pressure as shown on gauge. Compare pressure readings. If FRP PID reading is consistent and within 10 psi of fuel pressure at Schrader valve, go to step  10). If pressure readings are not as specified, go to next step.

  7. 7) Verify Fuel Rail Solenoid Shutoff Valve Opens

    Fuel rail solenoid shutoff valve is located on fuel rail. Turn ignition on. Using scan tool, access OUTPUT TEST MODE. Turn all outputs on and off several times by toggling Start and Stop button on scan tool. If fuel rail solenoid shutoff valve cannot be heard or felt operating, go to next step. If fuel rail solenoid shutoff valve can be heard or felt operating, replace FRP sensor and verify symptom no longer exists.

  8. 8) Check Voltage At Fuel Rail Solenoid Shutoff Valve

    Turn ignition on. Using scan tool, access OUTPUT TEST MODE. Turn all outputs on. Measure voltage between POWER CIRCUIT terminal and GROUND CIRCUIT terminal at fuel rail solenoid shutoff solenoid wiring harness connector. See Fig 3.
    NOTE: When energized by scan tool, PWR circuit to fuel rail solenoid shutoff valve will remain on for only 8 seconds.

    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 and verify symptom no longer exists.

    Fig 3: Identifying Fuel Rail Solenoid Shutoff Valve Connector Terminals
    G96J29131Courtesy of FORD MOTOR CO.

  9. 9) Check For Open Circuit

    Leave scan tool connected and ignition on. Using scan tool, access OUTPUT TEST MODE. Turn all outputs on. Measure voltage between POWER CIRCUIT terminal at fuel rail solenoid shutoff valve wiring harness connector and battery negative terminal. If voltage is 10.5 volts or less, repair open in power circuit. If voltage is more than 10.5 volts, repair open in ground circuit. Verify symptom is no longer present.

  10. 10) Verify Fuel Rail Solenoid Shutoff Valve Seals

    Ensure fuel pressure gauge is connected with vent hose. Release fuel pressure in fuel injector rail back to fuel tanks. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Turn ignition on or start engine. Turn ignition off. Disconnect fuel rail solenoid shutoff valve connector. Crank engine for 3 seconds. Turn ignition off and wait 2 minutes. Using scan tool, select FRP PID. Turn ignition on. If PID reading is less than 10 psi (70 kPa), go to next step. If PID reading is 10 psi (70 kPa) or more, replace fuel rail solenoid shutoff valve.

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

    Release fuel pressure in fuel injector rail back to fuel tanks. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Ensure fuel rail solenoid shutoff valve is disconnected. Turn ignition on, with engine off. Turn ignition off. Reconnect fuel rail solenoid shutoff valve connector. Turn ignition on, with engine off. Using scan tool, select FRP PID and note PID pressure reading. Note fuel pressure as shown on fuel pressure gauge. Compare pressure readings. If FRP PID reading is within 10 psi of fuel pressure at Schrader valve, go to next step. If pressure readings are not within 10 psi, replace fuel rail solenoid shutoff valve. Verify symptom is no longer present.

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

    Release fuel pressure in fuel injector rail back to fuel tanks. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Disconnect fuel rail solenoid shutoff valve connector. Turn ignition on, with engine off. Turn ignition off. Reconnect fuel rail solenoid shutoff valve connector. Turn ignition on and immediately start engine. Increase engine speed to 2500 RPM while monitoring FRP PID pressure reading. Note fuel pressure as shown on fuel pressure gauge. Compare pressure readings. If FRP PID reading is within 10 psi of fuel pressure at Schrader valve, go to next step. If pressure readings are not within 10 psi, replace fuel rail solenoid shutoff valve. Verify symptom is no longer present.

  13. 13) Check Fuel Pressure

    Start engine and allow it to idle. Using scan tool, select FRP PID. Note PID pressure reading. Increase engine speed to 2500 RPM. Again, note PID pressure reading. If PID pressure reading at idle is 80-120 (552-827 kPa) and more than 80 psi (552 kPa) with engine speed at 2500 RPM, turn ignition off and go to next step. If PID pressure reading 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 no longer exists.

  14. 14) Check Fuel Pressure Regulator Thermostat

    Start engine. 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 off and go to next step. If temperature is less than 59°F (15°C), check coolant lines. Repair as necessary and retest. If coolant lines are okay, replace fuel pressure regulator. If temperature is more than 140°F (60°C), replace fuel pressure regulator. Verify symptom no longer exists.

  15. 15) Check Fuel Injector Flow

    Turn ignition on. Using scan tool, select FRP PID. Note PID pressure reading. Connect Fuel Injector Tester (164-R3795) to suspect fuel injector. Set pulse width to 200 milliseconds and activate fuel injector tester. Again, note PID pressure reading. Compare pressure readings. Repeat procedure for remaining fuel injectors. If initial PID pressure reading is 35-50 psi (241-345 kPa) and each injector PID pressure reading is within 3 psi (20 kPa) of each other, no problem is indicated at this time. If symptom still exists, go to TROUBLE SHOOTING - NO CODES - EEC-V article.

  16. 16) Check For Fuel Leak

    Turn ignition off. Inspect fuel system for obvious signs of fuel leaking. If fuel system looks okay, release fuel system pressure. Install fuel pressure gauge. Turn ignition on. Fuel pressure should be more than 85 psi (586 kPa). Cover fuel system using soapy water solution. If no bubbles develop, fuel leaks cannot be found and testing is complete. If bubbles develop, isolate fault and repair as necessary.
    NOTE: If vehicle has sat for several hours with engine off, a slight natural gas smell may be detected around the intake manifold area. This is a normal condition.

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

    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

    Place shift selector in Park. Start engine and allow to idle. Using scan tool, select TANKPR PID from NGVM menu. Note TANKPR PID pressure reading. Using scan tool, select FRP PID from PID/DATA monitor menu. Note FRP PID pressure reading. Locate approximate TANKPR PID value and note PCM referenced pressure. See FUEL TANK PRESSURE SPECIFICATIONS  table. If PCM referenced pressure specification listed is within 22 psi (plus or minus) of FRP PID value that was recorded, no problem is indicated at this time. Service any other DTCs that are present. If PCM referenced pressure specification is not within 22 psi of FRP PID value, go to next step (DTC P1180) or replace fuel pressure regulator (DTC P1181).
    FUEL TANK PRESSURE SPECIFICATIONS

    TANKPR PID Value psi (kPa) PCM Referenced Pressure psi (kPa)
    290 (2000) 109 (752)
    580 (4000) 107 (738)
    870 (6000) 106 (731)
    1160 (8000) 105 (724)
    1450 (10,000) 103 (710)
    1740 (12,000) 102 (703)
    2030 (14,000) 101 (696)
    2321 (16,000) 100 (690)
    2611 (18,000) 99 (683)
    2901 (20,000) 98 (676)
    3191 (22,000) 97 (669)
    3481 (24,000) 96 (662)
    34061 (28,000) 95 (655)
    4351 (30,000) 94 (648)

  19. 19) Check Fuel Filter

    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 For Restricted Fuel Line

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