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MBE 900 FUEL INJECTION TROUBLESHOOTING

There are five fuel injection system tests which measure fuel delivery performance of the MBE 900 engine. Perform the following tests and make corrections or use the troubleshooting tables: ‪

  • Test #1: Downstream Pressure Test
  • Test #2: Flow Test At Nozzle Holder
  • Test #3: Flow Test At Fuel Filter
  • Test #4: Upstream Pressure Test
  • Test#5: Leak Test

General Fuel System Information and Troubleshooting

The fuel system contains five sub-systems. See Figure 42900 . The five sub-systems are: ‪

  • Fuel feed
  • Fuel return
  • Fuel delivery, low pressure side
  • Fuel delivery, high pressure side
  • Fuel drain

    1. Fuel Pump ‪

    10. Nozzle Holder ‪

    2. Check Valve (in fuel pump) ‪

    11. Overflow Valve ‪

    3. Pressure Limiting Valve ‪

    12. Constant Ventilation (overflow) ‪

    4. Main Fuel Filter ‪

    13. Air Admission Valve ‪

    5. Drain Valve ‪

    14. Fuel Tank ‪

    6. Constant Ventilation (in fuel filter) ‪

    15. Assembly Valve (in return line) ‪

    7. Fuel Temperature Sensor ‪

    16. Assembly Valve (in feed line) ‪

    8. Unit Pump (fuel injection) ‪

    17. Check Valve (in pre-filter) ‪

    9. Bypass (to fuel return port) ‪

    18. Fuel Pre-filter ‪

    Fuel System Schematic

  • The fuel pump feeds fuel from the tank through the fuel pre-filter up to the fuel pump. This is the fuel feed sub-system. ‪

    The fuel pump delivers fuel at low pressure to the fuel filter, and from there to the unit pumps (individual fuel injection pumpsone for each cylinder). On the way, a fuel temperature sensor monitors the flow downstream from the filter. This is the low pressure side of the fuel delivery sub-system. ‪

    Each unit pump delivers fuel at high pressure to the fuel injectors. This is the high pressure side of the fuel delivery sub-system. ‪

    Excess fuel enters the return sub-system through a leak line. The leak line collects unused fuel and empties through an overflow valve. The return lines bring the fuel back to the fuel tank. This is the fuel return sub-system. ‪

    Fuel caught in the fuel filter drains bank to the return line. This is the fuel drain sub-system. ‪

Principles of Operation

The fuel pump controls the delivery of fuel from the fuel tank to the unit pumps. Fuel pressure downstream of the fuel filter ranges from 400 to 650 kPa (58 to 94 psi). The fuel pump has a pressure limiting valve to prevent fuel pressure from getting too high (920 kPa [133 psi]) and a check valve to prevent pressure from getting too low (20 kPa [3 psi]). See Figure 42901 . ‪

1. Fuel Pump ‪

9. Fuel Return Port ‪

2. Main Fuel Filter (secondary) ‪

10. Unit Pump ‪

3. Fuel Delivery Port (to unit pumps) ‪

11. Return Line ‪

4. Fuel Leak Port ‪

12. Fuel Pre-filter ‪

5. Nozzle Holder ‪

13. Fuel Feed Line (from pre-filter to fuel pump) ‪

6. Transfer Tube ‪

14. Assembly Valve (in fuel feed line) ‪

7. Injector Line ‪

15. Assembly Valve (in fuel return line) ‪

8. Overflow Valve ‪

Fuel Circuit Flow Diagram

Fuel is twice filtered, once in a pre-filter upstream of the fuel pump, and for the second time in the main filter downstream of the fuel pump. The main filter has a drain valve to return fuel caught in the filter to the fuel tank and constant ventilation to reduce and return any fuel vapor to the tank. ‪

Unit pumps, one for each cylinder, boost minimum fuel pressure to 24,500 kPa (3553 psi) for purposes of injection. The fuel passes through a high-pressure line, a high-pressure connector inserted into the wall of the cylinder head, and finally into the nozzle holder, where it is injected into a specially-designed swirl cup in the head of the piston. ‪

Software maps in the DDEC-ECU control unit regulate the timing and amount of fuel injected. Both fuel consumption and horsepower can be changed by downloading different software mapping. ‪

Unused fuel is not wasted. It runs off into a leak line which is controlled by a 450 kPa (65 psi) overflow valve and returned to the fuel tank. The overflow valve is also equipped with constant ventilation to reduce and return fuel vapor. ‪

Troubleshooting Tests

Perform the following troubleshooting tests on the engine: ‪

  1. Run the engine for two to three minutes at rated speed, 2500 rpm.

    NOTICE:

    Correct torque on the high pressure lines is critical. Incorrect torques could result in leaks or lack of power due to restricted fuel flow. ‪

  2. Perform a visual inspection of all fuel lines, pressure fittings, and components, including all the fittings that connect the fuel feed and drain hoses to the fuel filter housing. Replace any components found to be damaged or leaking. If necessary, tighten all high-pressure fittings 25 Nm (18 lbft) and all banjo bolts 40 Nm (30 lbft).
  3. Inspect the filter element in the fuel pre-filter. Replace if necessary.
  4. Inspect the filter element in the main fuel filter. Replace if necessary.
  5. On engines with speed governors, connect minidiag2 to the vehicle and increase the engine speed to 4000 rpm. Note the governed engine speed given.
  6. Continue to run the engine until it reaches the operating temperature of approximately 180F (82C). When the operating temperature has been reached, shut the engine down and go to the next step.

    Note: When doing these tests, be sure the temperature of the fuel in the fuel tank is no higher than 104F (40C). Collect any fuel which flows out during the test. The fuel should flow through free of bubbles.

  7. Do the fuel system troubleshooting tests and correct any problems. As indicated by the test results, do any follow-up tests or troubleshooting tables, as required. Make the necessary repairs and/or replacements. For troubleshooting tests and tables see the following subjects:
    1. Test #1: Downstream Pressure Test
    2. Test #2: Flow TestAt Nozzle Holder
    3. Test #3: Flow TestAt Fuel Filter
    4. Test #4: Upstream Pressure Test
    5. Test #5: Leak Test
    6. Troubleshooting tables
  8. When all the tests are completed, the test equipment removed, and all repairs/replacements have been made, bleed the fuel system.
    1. If equipped with a hand pump on the fuel/water separator, work the hand pump 50 times.
    2. Crank the engine for 30 seconds at a time, but no longer . Before cranking the engine again, wait at least two minutes. The engine should start within four 30-second attempts. The fuel system is bled automatically.
  9. If the problem has still not been resolved, test vehicle performance on a chassis dynamometer. If there is no improvement in fuel consumption or performance, connect a fuel consumption measuring system.

Test #1: Downstream Pressure Test

Perform the following test set-up and test to determine the downstream pressure: ‪

Test Set-Up

  1. Remove the engine trim panel. See Figure 42902 .

    1. Engine Trim Panel ‪

    3. Fuel Temperature Sensor ‪

    2. Engine Wiring Harness ‪

    Test Setup #1: Downstream Pressure Test

  2. Disconnect the fuel temperature sensor. See Figure 42903 .

    1. Fuel Temperature Sensor ‪

    2. Engine Wiring Harness ‪

    Disconnecting the Sensor

  3. Plug the disconnected fuel temperature sensor into the engine wiring harness and tie it up out of the way.
  4. Install the adaptor and seal from the fuel adaptor parts kit, J-46377 . See Figure 42904 .

    1. Banjo Fitting ‪

    Connecting the Adaptor

  5. Attach a banjo fitting to the adaptor, and use that to connect the high-pressure fuel line J-46372 and gauge J-46378 to the adaptor.
Test

  1. Open the fuel fill cap to release pressure in the fuel tank.
  2. Start the engine and run it at a slow idle, 600 to 650 rpm.
  3. Read off the fuel pressure on the high-pressure gauge. The gauge should read at least 430 kPa (62 psi).
    1. If the fuel pressure is too low, do test #3: Flow TestAt Fuel Filter, and correct the problem. Refer to section .
  4. Increase the engine speed to 2500 rpm.
  5. Read off the fuel pressure on the high-pressure gauge. The gauge should read from 400 to 650 kPa (58 to 94 psi).
    1. If the fuel pressure is within limits, do test #2: Flow TestAt Nozzle Holder, and correct the problem. Refer to section .
    2. If the fuel pressure is too low, do test #3: Flow TestAt Fuel Filter, and correct the problem. Refer to section .
    3. If the fuel pressure is too high, see the causes listed in Table , Problem The Fuel Pressure is Too High Downstream of the Fuel Filter, and correct the problem. Make any necessary repairs and/or replacements.
  6. Remove all test equipment. Reconnect the fuel temperature sensor.
  7. Make sure the fuel fill cap is tightly closed and the vehicle has been restored to operating condition.

Test #2: Flow Test At Nozzle Holder

Perform the following test set-up and test to determine the flow at the nozzle holder: ‪

Test Set-Up

  1. Remove the engine trim panel. See Figure 42905 .

    1. Engine Trim Panel ‪

    2. Fuel Return Line ‪

    Test Setup #2: Flow Test at Nozzle Holder

  2. Using the injector line socket J-46371 , remove the injection line at cylinder #4 on the 6-cylinder engine, and at cylinder #2 on the 4-cylinder engine.
  3. Remove the fuel return line from the cylinder head at the same cylinder from which the injection line was removed.
  4. Install an adaptor and seal ring from the fuel adaptor parts kit J-46377 . Use the adaptor to install the fuel return line back onto the cylinder head.
  5. Install the injection line, as removed.
  6. Place a clean cloth below the opening in the adaptor to catch any fuel which leaks out of the return line during the test.
Test

  1. Open the fuel fill cap to release pressure in the fuel tank.
  2. Start the engine and run it at a slow idle, 600 to 650 rpm until the adaptor opening appears moist.

    If fuel or coolant flows out of the return line, see the causes listed in Table , Problem Fuel Flows Out of the Fuel Return Line, and correct the problem. Make any necessary repairs and/or replacements. ‪

  3. Increase the engine speed to 2500 rpm. At most, drops of fuel should appear at the adaptor opening.

    If fuel or coolant flows out of the return line, see the causes listed in Table , Problem Fuel Flows Out of the Fuel Return Line, and correct the problem. Make any necessary repairs and/or replacements. ‪

  4. Remove the adaptor and seal ring J-46377 . Restore the fuel return line to the original installation, as removed.
  5. Make sure the fuel fill cap is tightly closed and the vehicle has been restored to operating condition.

Test #3: Flow Test At Fuel Filter

Perform the following test set-up and test to determine the flow at the fuel filter: ‪

Test Set-Up

  1. Remove the engine trim panel. See Figure 42906 .

    1. Fuel Drain Line (at filter) ‪

    6. Banjo Bolt Union (from kit) ‪

    2. Drain Line Fitting ‪

    7. Banjo Fitting ‪

    3. Main Filter Housing (secondary) ‪

    8. Overflow Valve ‪

    4. Engine Trim Panel ‪

    9. Clean Container ‪

    5. FuelReturn Line (at injector) ‪

    10. Hose ‪

    Test Setup #3: Flow Test at Fuel Filter

  2. Disconnect the fuel return line at the overflow valve. When loosening the banjo bolt, hold a second wrench on the overflow valve to avoid loosening the valve.
  3. Using a banjo bolt, nut, and washer from the fuel adaptor parts kit J-46377 , seal off the fuel return line.
  4. In place of the fuel return line, attach the hose with a banjo fitting from the fuel adaptor parts kit J-46377 to the overflow valve. When tightening the union, hold a second wrench on the overflow valve to avoid over-tightening the valve.
  5. At the main fuel filter, detach the fuel drain line and its fitting from the main filter housing.
  6. In place of the fuel drain line, attach a union from the fuel adaptor parts kit to the main filter housing.
  7. At the union, attach a hose and run the other end of the hose into another clean container.
Test

  1. Open the fuel fill cap to release pressure in the fuel tank.
  2. Start the engine and run it at a slow idle, 600 to 650 rpm until the fuel flows into the container with little or no bubbling.
  3. Check the fuel flow at the fuel filter.

    Note: When beginning the timed portion of this test, take the transparent hose out of the clean container and insert it into a calibrated container or measuring cup.

    1. Measure the quantity of fuel that flows out of the hose in one minute (60 seconds). If more than 10.1 fluid ounces (300 mL) flow out, fuel flow at the filter is too high (at idle).
    2. Increase the engine speed to 2500 rpm.
    3. Measure the quantity of fuel that flows out of the hose in one minute. If more than 10.1 fluid ounces (300 mL) flow out, fuel flow at the filter is too high (at rated speed).
    4. Note: If fuel flow on either test is too high, correct the problem. Fuel flow is OK if the system passes both tests.

  4. Check the fuel flow at the overflow valve.
    1. Reduce engine speed back to slow idle, 600 to 650 rpm.

      Note: When beginning the timed portion of this test, take the transparent hose out of the clean container and insert it into a large calibrated container.

    2. Measure the quantity of fuel that flows out of the hose in one minute (60 seconds). If more than 1.7 Liter (1.8 qt) flows out, overflow valve fuel flow is too high.

      If less than 0.9 Liter (0.95 qt) flows out, overflow valve fuel flow is too low. ‪

      If between 0.9 Liter (0.95 qt) and 1.7 Liter (1.8 qt) flows out, overflow valve fuel flow is within range. ‪

    3. Increase the engine speed to 2500 rpm.
    4. Measure the quantity of fuel that flows out of the hose in one minute. If more than 7.5 Liter (7.9 qt) flows out, overflow fuel flow is too high.

      If less than 2.7 Liter (2.9 qt) flows out, overflow fuel flow is too low. ‪

      If between 2.7 Liter (2.9 qt) and 7.5 Liter (7.9 qt) flows out, overflow fuel flow is within range. ‪

  5. If overflow valve fuel flow is too low and filter fuel flow is too high, see the causes listed in Table , Problem Fuel Flow Quantity is Too Low at the Overflow Valve and Too High at the Filter, and correct the problem. Make any necessary repairs and/or replacements.

    If overflow valve fuel flow is too low and fuel flow is OK at the filter, see the causes listed in Table , Problem Fuel Flow Quantity is Tool Low at the Overflow Valve and Within Range at the Filter, and correct the problem. Make any necessary repairs and/or replacements. ‪

    If overflow valve fuel flow is too low and fuel flow is also too low at the filter, do test #4: Upstream Pressure Test. Refer to section . ‪

    If overflow valve fuel flow is OK and no fuel flows out at the filter, the continuous ventilation port in the fuel filter is blocked by impurities. Open the fuel filter and clean or replace the blocked port. ‪

    If overflow valve fuel flow is OK and fuel flow is also OK at the filter, the overflow valve is faulty, leaking, jammed open, worn, or incorrectly installed. Replace the overflow valve. ‪

    Note: Do not attempt to disassemble the overflow valve. The overflow valve cannot be repaired.

  6. Remove the union, transparent hose, banjo bolt, and nut. Restore the fuel return and drain lines to the original installation, as removed.
  7. Make sure the fuel fill cap is tightly closed and the vehicle has been restored to operating condition.

Test #4: Upstream Pressure Test

Perform the following test set-up and test to determine the upstream pressure: ‪

Test Set-Up

  1. At the main filter housing, disconnect the fuel feed line and feed line fitting. This fitting is aft of the fuel return line and connects to the fuel pre-filter. See Figure 42907 .

    1. Main Filter Housing ‪

    3. Test Hose ‪

    2. Check Valve ‪

    4. Fuel Feed Line ‪

    Test Setup #4: Upstream Pressure Test

  2. Install the pressure tester J-46380 . Connect one end of the transparent test hose to the fuel pre-filter, using a union from the fuel adaptor parts kit J-46377 . Connect the other end of the transparent test hose to the disconnected fuel feed line, using a barbed adaptor to the proper sized fuel line fitting.

    Note: The opening arm of the union at the pre-filter should press open the check valve.

  3. Inspect the seals at the fitting on the fuel pre-filter for damage and replace if necessary.
  4. Bleed the fuel system.
    1. If equipped with a hand pump on the fuel/water separator, work the hand pump 50 times.
    2. Crank the engine for 30 seconds at a time, but no longer . Before cranking the engine again, wait at least two minutes. The engine should start within four 30-second attempts. The fuel system is bled automatically.
  5. Stand the pressure tester on a level spot, such as the frame rail.

    Note: The pressure tester must be level to indicate correctly.

Test

  1. Open the fuel fill cap to release pressure in the fuel tank.
  2. Start the engine and run it at a slow idle, 600 to 650 rpm.

    Note: The pressure tester reads in bar. 1 bar = 14.5 psi or 100 kPa.

    Note: This test measures suction at the fuel inlet. All pressure values are negative.

  3. Read off the fuel pressure on the pressure tester. The gauge should read from 0.09 bar to 0.12 bar (1.3 to 1.7 psi [9 to 12 kPa]).

    If the fuel pressure is too low (less suction), see the causes listed in Table , Problem The Inlet Pressure is Too Low, and correct the problem. Make any necessary repairs and/or replacements. ‪

    If the fuel pressure is too high (more suction), see the causes listed in Table , Problem The Inlet Pressure is Too High, and correct the problem. Make any necessary repairs and/or replacements. ‪

  4. Increase the engine speed to 2500 rpm.
  5. Read off the fuel pressure on the pressure tester. The gauge should read between 0.4 and 0.5 bar (5.8 to 7.3 psi [40 to 50 kPa]).

    If the fuel pressure is too low (less suction), see the causes listed in Table , Problem The Inlet Pressure is Too Low, and correct the problem. Make any necessary repairs and/or replacements. ‪

    If the fuel pressure is too high (more suction), see the causes listed in Table , Problem The Inlet Pressure is Too High, and correct the problem. Make any necessary repairs and/or replacements. ‪

  6. Remove all test equipment. Reconnect the fuel feed line.
  7. Make sure the fuel fill cap is tightly closed and the vehicle has been restored to operating condition.

Test #5: Leak Test

Perform the following test set-up and test to determine the if and where the fuel system is leaking: ‪

Test Set-Up

  1. Remove the engine trim panel. See Figure 42908 .

    1. Engine Trim Panel ‪

    4. Cap ‪

    2. Main Filter Housing ‪

    5. Fuel Return Line ‪

    3. Fitting ‪

    6. Fuel Feed Line ‪

    Test Setup #5: Leak Test

  2. Disconnect the fuel temperature sensor. See Figure 42903 .

    1. Fuel Temperature Sensor ‪

    2. Engine Wiring Harness ‪

    Disconnecting the Sensor

  3. Plug the disconnected fuel temperature sensor into the engine wiring harness and tie it up out of the way.
  4. Install the adaptor and seal from the fuel adaptor parts kit J-46377 . See Figure 42904 .

    1. Banjo Fitting ‪

    2. Unit Pump (fuel) ‪

    Connecting the Adaptor

  5. Attach a banjo fitting to the adaptor, and use that to connect the high-pressure fuel line J-46372 and gauge J-46378 .
  6. Disconnect the fuel return line at the main filter housing. Seal the opening with a cap.
  7. Disconnect the fuel feed line and feed line fitting at the main filter housing. In their place, attach the hose with a banjo fitting and the shut-off lever from the fuel adaptor parts kit J-46377 .
Test

  1. Open the fuel fill cap to release pressure in the fuel tank.
  2. Fill the low-pressure fuel circuit with compressed air until the fuel pressure on the high-pressure gauge reads 1000 kPa (145 psi).
  3. Turn the shut-off lever to the OFF position and wait five minutes.
  4. At the end of five minutes, read the pressure on the gauge again. The gauge should read at least 975 kPa (141 psi).

    If the gauge pressure is too low, see the causes listed in Table , Problem The Low Pressure Fuel System is Leaking, and correct the problem. Make any necessary repairs and/or replacements. ‪

  5. Check the engine oil for presence of fuel.

    If there is fuel in the engine oil, see the causes listed in Table , Problem The Low Pressure Fuel System is Leaking,and correct the problem. Make any necessary repairs and/or replacements. ‪

  6. Open the shut-off valve and remove all the test equipment. Connect the fuel feed and return lines, as removed. Reconnect the fuel temperature sensor.
  7. Make sure the fuel fill cap is tightly closed and the vehicle has been restored to operating condition.