Cummins ISX11.9 CM2250 – Service Manual 006-003   Air in Fuel

Perform the steps in the following procedure before beginning this procedure, to make sure all entrapped air is removed from the system. Refer to Procedure 005-234 in Section 5.

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

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

NOTE: A symptom of air-in-fuel for the engines equipped with a common rail fuel system is an audible surge associated with fuel system pressure fluctuations, due to air in the fuel supply.

The following test method will simulate rated fuel flow through the system, so that air-in-fuel problems can be diagnosed.

Start the engine and run the engine speed from idle to high idle several times to purge the air induced when the diagnostic fuel line was installed.

Observe the fuel flow exiting the diagnostic fuel line while the engine runs at idle speed.

A few bubbles exiting the line is expected. A foamy appearance is an indication of a leak that allows air to enter, a severe inlet restriction that causes cavitation, or a system that is not yet primed.

Use the following procedure to check inlet restriction. Refer to Procedure 006-020 in Section 6. If the fuel inlet restriction is not excessive, the source of air entry must be isolated to one of the following:

• Suction fuel lines
• OEM fuel lines
• Suction side fuel filter assemblies
• Lift pump gasket or fittings
• Stand-pipe(s) in the fuel tank(s).

• Remove all test fuel lines.
• Operate the engine and check for leaks.