Fuel Injectors & Pumps – Section 8.10 MBE 900 Upstream Pressure Test

Section 8.10
MBE 900 Upstream Pressure Test

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

1. At the main filter housing, disconnect the fuel feed line and feed line fitting. This fitting is after the fuel return line and connects to the fuel pre-filter.
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. Stand the pressure tester on a level spot, such as the frame rail.

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

5. Open the fuel fill cap to release pressure in the fuel tank.
6. Start the engine and run it at a slow idle.

   Note: The pressure tester reads in bar. 1 bar = 14.5 psi or 100 kPa. The test measures suction at the fuel inlet. All pressure values are negative.

7. 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) or if fuel pressure is too high (more suction), see the causes listed in troubleshooting table in current MBE 900 service manual (6SE414).
8. Increase the engine speed to 2500 rpm.
9. Read off the fuel pressure on the pressure tester. The gauge should read from – 0.4 to – 0.5 bar (– 5.8 to – 7.3 psi [– 40 to – 50 kPa]).
10. Remove all test equipment. Reconnect the fuel feed line.