Fuel Injectors & Pumps – Section 8.9 MBE 900 Flow Test At Fuel Filter

Section 8.9
MBE 900 Flow Test At Fuel Filter

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

1. Remove the engine trim panel. See current MBE 900 service manual (6SE414) .
2. Disconnect the fuel return line at the overflow valve. When loosening the banjo bolt, hold a second wrench on the overflow 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 (J46377) 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.
8. Open the fuel fill cap to release pressure in the fuel tank.
9. 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.
10. Check the fuel flow at the fuel filter. 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 300 ml (10.1 fluid ounces) 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 300 ml (10.1 fluid ounces) flow out, fuel flow at the filter is too high (at rated speed). If the fuel flow on either test is too high, correct the problem. Fuel flow is OK if the system passes both tests.
11. Check the fuel flow at the overflow valve.
    1. Reduce engine speed back to slow idle, 600 to 650 rpm.
    2. Measure the quantity of fuel that flows out of the hose in one minute (60 seconds). If more than 1.7 Liters (1.8 qt) flows out, the overflow valve fuel flow is too high. If less than 0.9 Liter (.95 qt) flows out, the overflow valve fuel flow is too low. If between 0.9 Liter (.95 qt) and 1.7 Liters (1.8 qt) flows out, the overflow valve fuel flow is within range.
    3. Increase the engine speed to 2500 rpm.
    4. Measure the quantity of fuel that flowed out of the hose in one minute. If more than 7.5 Liters (7.9 qt) flows out, the over flow fuel flow is too high. If less than 2.7 Liters (2.9 qt) flows out, the overflow fuel flow is too low. If between 2.7 Liters (2.9 qt) and 7.5 Liters (7.9 qt) flows out, the overflow fuel flow is within range.
12. If overflow valve fuel flow is too low and filter fuel flow is too high, or if fuel flow is too low and fuel flow is OK, see the causes in troubleshooting table in current service manual. If the overflow valve fuel flow is too low and the fuel flow is also too low at the filter, do upstream pressure test. 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.

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

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