MBE 4000 DDEC VI Troubleshooting – Section 3.6 Test #4 Upstream Pressure Test (Pump Suction)

Section 3.6
Test #4 Upstream Pressure Test (Pump Suction)

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

Section 3.6.1
Test #4 Set-Up

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

1. At the Motor Control Module (MCM), disconnect the fuel feed line. See Figure "Test Setup #4 Upstream Pressure Test" .
   

   1. Adapter Assembly Valve (part of J-46377–A)‪	3. Test Hose (part of J-46380)‪
   2. Fuel Filter Assembly‪	4. Fuel Supply Line‪

   Figure 1. Test Setup #4 Upstream Pressure Test

2. Install the pressure tester (J-46380) . Connect one end of the transparent test hose to the MCM cooler, using a union from the fuel adaptor parts kit (J-46377-A) . 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: Ensure the correct assembly valve adapter from parts kit (J-46377-A) is used on the MCM side. Using the incorrect fitting will not allow the assembly valve on the MCM to open.

3. Prime the fuel system.
   1. If equipped with a hand pump on the fuel/water separator, work the hand pump until resistance is felt.

      PERSONAL INJURY ‪
      To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked.‪

   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.
4. Stand the pressure tester on a level spot, such as the frame rail.

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

Section 3.6.2
Test #4

Perform the following:‪

1. Open the fuel fill cap to release pressure in the fuel tank.

   PERSONAL INJURY ‪
   To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked.‪

2. Start the engine and run it at a slow idle, 600 to 650 rpm.

   Note: The pressure tester reads in bar. 0.35 bar = 5.0 psi.

   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 –0.30 and –0.45 bar (–4.4 to –6.5 psi).

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

4. Increase the engine speed to 1900 rpm.
5. Read off the fuel pressure on the pressure tester. The gauge should read between–0.30 and –0.45 bar (–4.4 to –6.5 psi).

   If the fuel pressure is too low (less suction), see the causes listed in Table "Problem — The Fuel Inlet Pressure is Too Low" , “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 Fuel Inlet Pressure is Too High" , “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. Ensure the fuel fill cap is tightly closed and the vehicle has been restored to operating condition.

   Problem — The Fuel Inlet Pressure is Too Low ‪
   Possible Cause ‪	Remedy ‪
   The pre-filter is leaking (drawing air).‪	Replace the O-ring. Replace the filter element and tighten the cap on the filter housing 25 N·m (18 lb·ft).‪
   The fuel feed lines and connections are leaking (drawing air).‪	Replace the seals on the leaking lines. Tighten the fittings on the fuel lines to 35 N·m (26 lb·ft) and perform a fuel leak test.‪
   The fuel pump is worn.‪	Replace the fuel pump.‪
   The pressure limiting valve in the fuel pump is jammed open or the drive lever is loose or broken.‪	Replace the fuel pump.‪
   The air-admission valve in the fuel tank is blocked.‪	Remove air-admission valve blockage.‪
   The suction line and/or strainer at the fuel level sensor is blocked or is touching the bottom of the fuel tank.‪	Inspect the suction line and/or strainer through the fuel fill opening in the fuel tank. Remove the fuel level sensor and repair or replace the line or strainer, as necessary.‪

   Table 4. Problem — The Fuel Inlet Pressure is Too Low

   Problem — The Fuel Inlet Pressure is Too High ‪
   Possible Cause ‪	Remedy ‪
   The fuel feed lines are kinked or blocked.‪	Inspect the lines and fittings for blockage. Repair/replace as necessary.‪
   The suction line and/or strainer at the fuel level sensor is blocked or is touching the bottom of the fuel tank.‪	Inspect the suction line and/or strainer through the fuel fill opening in the fuel tank. Remove the fuel level sensor and repair or replace the line or strainer, as necessary.‪
   The check valve in the fuel feed line is blocked or not open wide (the flange at the fitting connection is bent).‪	Repair/replace as necessary.‪

   Table 5. Problem — The Fuel Inlet Pressure is Too High