Cummins ISX11.9 CM2250 – Service Manual 006-020   Fuel Inlet Restriction

Install orificed diagnostic fuel line, Part Number 3164621, onto the Compuchek™ fitting at the outlet to the fuel pump gear pump.

The orificed diagnostic fuel line is used in procedures to create rated flow through the low pressure fuel system without the need to operate the engine under load.

Obtain a container suitable for collection of fuel that exits the diagnostic fuel line. A 19 liter [5 gal] bucket is recommended.

Obtain banjo test fitting, Part Number 4919057, and install a 1/8 inch NPT Compuchek™ fitting, Part Number 3042618 or equivalent, into the banjo test fitting.

Remove the banjo fitting from the gear pump inlet and install the banjo test fitting. 

Attach a 0 to 762 mm-Hg [0 to 30 in-Hg] vacuum gauge to the banjo test fitting at the gear pump inlet.

NOTE: Measurements taken while the fuel lift pump is running will be inaccurate. Wait until the lift pump has completed its cycle before measuring the fuel inlet restriction.

Operate the engine at high idle and measure the inlet vacuum.

Fuel Inlet Restriction

If the inlet restriction is excessive, look for the root cause:

• Suction side fuel filter(s) or check valve restriction
• Fuel heater valves are restricted
• Lift pump or check valve restriction
• OEM fuel lines pinched or restricted
• Fuel tank stand pipes restricted
• Fuel pump gear pump fuel supply line restricted or damaged.

• Disconnect all diagnostic test fittings and install all components removed during testing. Refer to Procedure 006-024 in Section 6.
• If applicable, connect the fuel lift pump to the engine harness.