Cummins ISX11.9 CM2250 – Service Manual 005-236   Fuel System Diagnostics

WARNING  Wear appropriate eye and face protection when using compressed air. Flying debris and dirt can cause personal injury.

WARNING  When using a steam cleaner, wear safety glasses or a face shield, as well as protective clothing. Hot steam can cause serious personal injury.

CAUTION  Clean all fittings before disassembly. Dirt or contaminants can damage the fuel system.

Before servicing any fuel system components, (such as fuel lines, fuel pump, injectors, etc.) which would expose the fuel system or internal engine component to potential contaminants prior to disassembly, clean the fittings, mounting hardware, and the area around the component to be removed. Dirt or contaminants can be introduced into the fuel system and engine if the surrounding areas are not cleaned, resulting in damage to the fuel system and engine. Refer to Procedure 000-009 in Section 0.

To prevent engine damage from debris or contamination, cover, cap, or plug any openings as soon as possible when servicing the fuel system.  Caps and plugs can be found in Clean Care Kit, Part Number 4919073.

The following procedures are used to diagnose fuel system issues.  These checks and measurements are referenced throughout the applicable troubleshooting and fault code trees as needed.

This procedure is not intended to take the place of the troubleshooting tree repair direction.

Refer to the appropriate troubleshooting symptom tree for repair direction.

NOTE: This test can not be performed if the engine will not start.

Connect INSITE ™ electronic service tool.

Operate the engine.

Monitor the fuel rail pressure.

Check the fuel pressure decay.

Shut the engine off and wait for it to completely stop. Turn the keyswitch ON quickly.

Monitor INSITE™ electronic service tool and record the fuel rail pressure for 1 minute.

A decay in fuel pressure greater than 100 bar [1450 psi] in 1 minute is an indication of a high-pressure fuel system leak.

Refer to the appropriate troubleshooting symptom tree for repair direction.

The low-pressure system check consists of a number of measurements and checks to make sure that the low pressure fuel system is functioning properly. These checks will vary, depending on whether or not the engine will start.

Verify the fuel system has been primed. Refer to Procedure 005-234 in Section 5.

Check for air in the fuel. Refer to Procedure 006-003 in Section 6.

Measure the fuel inlet restriction. Refer to Procedure 006-020 in Section 6.

Measure the fuel gear pump output pressure. Use the instructions in the Fuel Pump Gear Pump Pressure Test section of this procedure.

Measure the fuel filter restriction. Use the instructions in the Fuel Filter Restriction section of this procedure.

Measure the fuel drain line restriction. Refer to Procedure 006-012 in Section 6.

Verify the fuel system has been primed. Refer to Procedure 005-234 in Section 5.

If the engine is equipped with a lift pump, measure the lift pump pressure. Use the instructions in the Fuel Lift Pump Pressure section of this procedure.

Measure the fuel gear pump output pressure while cranking. Use the instructions in the Fuel Pump Gear Pump Pressure Test section of this procedure.

Measure the fuel drain line restriction. Refer to Procedure 006-012 in Section 6.

Install a 0 to 2068 kPa [0 to 300 psi] pressure gauge at the Compuchek™ fitting at the outlet of the fuel pump gear pump.

Install a 0.043-inch orificed diagnostic fuel line, Part Number 3164621, at the outlet of the fuel filter head. Run the fuel hose into a suitable container.

Wait for the lift pump cycle to complete (approximately 60 seconds).

Operate the engine at high idle and observe the fuel gear pump pressure.

Gear Pump Pressure at High Idle

Install a 0 to 207 kPa [0 to 30 psi] pressure gauge at the Compuchek™ fitting at the outlet of the fuel pump gear pump.

Wait for the lift pump cycle to complete (approximately 60 seconds).

Crank the engine and observe the fuel gear pump pressure.

Gear Pump Pressure While Cranking At A Minimum of 150 RPM for 10 Seconds

Connect the fuel lift pump to the engine wiring harness after the measurements are completed.

Remove the threaded plug from the outlet side of the fuel filter head and install a Compuchek™ fitting, Part Number 3100221 or equivalent.

Install the orificed diagnostic fuel line, Part Number 3164621, at the Compuchek™ fitting.

Install a 0 to 2068 kPa [0 to 300 psi] pressure gauge at the Compuchek™ fitting at the outlet of the fuel pump gear pump.

Wait for the lift pump cycle to complete (approximately 60 seconds).

Operate the engine at high idle and observe the filter inlet pressure.

Install a 0 to 2068 kPa [0 to 300 psi] pressure gauge at the Compuchek™ fitting at the outlet to the fuel filter head.

Operate the engine at high idle and observe the filter outlet pressure.

Fuel Filter Restriction

If the difference between the filter inlet pressure and filter outlet pressure is greater than the specification, replace the fuel filter.

Install a 0 to 207 kPa [0 to 30 psi] pressure gauge at the Compuchek™ fitting at the inlet to the fuel filter head (outlet of the fuel pump gear pump).

Turn the ignition switch to the ON position to activate the lift pump. Repeat this action, if necessary.

Measure the fuel lift pump pressure.

Fuel Lift Pump Pressure

Remove the banjo bolt from the fuel pump head drain line at the fuel drain manifold.

Install a banjo flow adapter fitting, Part Number 3164618, at the fuel drain manifold. Route the hose to a graduated cylinder.

Close the engine cover while performing this measurement.

Perform INSITE™ electronic service tool High-Pressure Leakage Test.

Connect INSITE™ electronic service tool.

Start the engine and allow the engine to idle with fuel flowing into a collection device.

Wait for the lift pump cycle to complete (approximately 60 seconds).

Begin the High-Pressure Leakage Test.

Use a graduated cylinder to measure the volume of fuel flow from the fuel pump drain head over a 30 second time span while performing the high-pressure leakage test. This measurement should be taken three times, but only the third reading is to be used.

If 450 cc pump head drain flow is collected in less than 30 seconds, the fuel pump head has malfunctioned and must be replaced.

This specification is valid for engines operating on diesel fuels. Low fuel viscosity will increase the leakage rate; for example, kerosene or aviation fuels will result in excessive leakage. Verify the fuel type being measured before replacing a fuel pump head for excessive leakage.

Refer to the appropriate troubleshooting symptom tree for repair directions.

Close the engine cover while performing this measurement.

Wait for the lift pump cycle to complete (approximately 60 seconds).

Begin cranking the engine.

When fuel begins to exit the drain line, route the drain flow to a graduated cylinder and continue cranking for 30 seconds.

NOTE: Do not crank the engine for 30 seconds continously. Crank the engine in 15 second intervals with a 15 second pause between intervals. This reduces the possibility of overheating the starting motor.

This measurement must be taken three times, but only the third reading is used.

If 450 cc pump head drain flow is collected in less than 30 seconds, the fuel pump head has malfunctioned and must be replaced.

Refer to the appropriate troubleshooting symptom tree for repair directions.

NOTE: Make certain the engine is at operating temperature before beginning this test.

Remove the banjo bolt from the injector drain line at the fuel drain manifold.

Install a banjo flow adapter fitting, Part Number 3164618, to the fuel drain manifold. Route the hose into a graduated cylinder.

Close the engine cover(s) while performing these tests.

If the engine will start, perform INSITE™ electronic service tool High-Pressure Leakage Test.

Connect INSITE™ electronic service tool.

Start the engine and allow the engine to idle with fuel flowing into a collection device.

Begin the High-Pressure Leakage Test.

Use a graduated cylinder to measure the volume of fuel flow over a 60 second time span from the injector return while performing the high-pressure leakage test.

NOTE: Fuel temperature and fuel type will influence this measurement. For example; as the engine is warmed up and the injectors become hot, the leakage rate will increase. Also, low viscosity fuels, such as kerosene, will cause the leakage rate to increase. The above specification is correct for on-highway diesel fuels, where the diesel fuel inlet temperature is less than 49°C [120°F].

After recording the fuel leakage quantity, stop INSITE™ electronic service tool High-Pressure Leak Test and turn the keyswitch to OFF.

NOTE: Be sure a steady flow of fuel is present at the drain line before beginning the measurement. Air in the line and movement of the hose during measurement can result in inaccurate measurements.

If injector drain flow is excessive, it will be necessary to isolate injector(s) or fuel connector(s) that are damaged or worn.

A loose fuel connector retaining nut results in a poor seal at the interface between the fuel connector and the injector. The loose condition will result in leakage of high-pressure fuel to the injector drain.

Verify first that the fuel connectors are properly tightened. Refer to Procedure 006-052 in Section 6.

If loose retaining nut(s) are found, test for leakage after tightening the retaining nut(s).

Begin cranking the engine until fuel exits the drain line.

NOTE: Do not crank the engine for 30 seconds continously. Crank the engine in 15 second intervals with a 15 second pause between intervals. This reduces the possibility of overheating the starting motor.

When fuel begins to exit the drain line, route the drain flow to a graduated cylinder and continue cranking for 30 seconds.

The leakage should only be a few drops. Any more than a few drops indicates either an injector or a high-pressure connector malfunction.

Refer to the appropriate troubleshooting symptom tree for repair directions.

NOTE: Vent the pressure from the fuel system as directed after each cranking event.

WARNING  Normal engine operation creates highly pressurized fuel in the fuel line which will remain in the fuel line after engine shutdown. Never open the fuel system when the engine is operating. Before servicing the fuel system, always loosen the pump to rail fuel line at the rail to vent the pressure. Keep hands clear of the line when loosening. High pressure fuel spray can penetrate the skin, resulting in serious personal injury or death.

Before servicing the high-pressure fuel system, loosen the pump to rail line at the rail, to vent the pressure.

Keep hands clear of the line when loosening the rail line.

Tighten the fuel rail nut.

NOTE: A machined slot in this fitting directs the fuel spray toward the engine.

CAUTION  Do not install the isolation tool at the high pressure pump outlet fitting. Severe engine damage will result. This tool must only be installed at the fuel rail for the purpose of isolating the high-pressure fuel supply from individual injectors.

CAUTION  Make certain the keyswitch is in the OFF position (engine not running) when loosening or tightening high-pressure fuel lines.

Use leak test isolation tool, Part Number 4918563, to isolate excessive fuel drain from injectors or fuel connectors.

Follow the pressure relief step (shown in the previous step) prior to every installation of the isolation tool.

Isolate the injector and fuel connector for each cylinder by installing the isolation tool at the fuel rail in place of the high-pressure fuel line that supplies the fuel connector.

If the engine will not start, drain flow must be measured while engaging the starting motor for 30 seconds.

NOTE: Do not crank the engine for 30 seconds continously. Crank the engine in 15 second intervals with a 15 second pause between intervals. This reduces the possibility of overheating the starting motor.

Record the amount of fuel flow from the injector drain line in 1 minute while the engine is running. Use the INSITE™ electronic service tool High-Pressure Leakage Test. Do this up to six (6) times, once while each line is isolated.

If isolating a single injector and high-pressure fuel connector causes the leakage to decrease significantly, compared to the rest of the set, that injector and fuel connector must be inspected.

NOTE: Be sure a steady flow of fuel is present at the drain line before beginning the measurement. Air in the line and movement of the hose during measurement can result in inaccurate measurements.

Inspect the suspect fuel connector. Refer to Procedure 006-052 in Section 6. If the fuel connector is not damaged, replace both the injector and the fuel connector.

Remove the banjo bolt from the fuel pressure relief valve drain line at the fuel drain manifold.

Install a banjo flow adapter fitting, Part Number 3164618, at the fuel drain manifold. Route the hose from this adapter to a graduated cylinder.

Perform INSITE™ electronic service tool High-Pressure Leakage Test.

Connect INSITE™ electronic service tool.

Start the engine and allow the engine to idle with fuel flowing into a collection device.

Begin the High-Pressure Leakage Test.

When fuel begins to exit the drain line, route the drain flow into a graduated cylinder.

The leakage must be less than 10 drops per minute.

Refer to the appropriate troubleshooting symptom tree for repair directions.

NOTE: If Fault Code 449 or 2311 is active, do not replace the fuel pressure relief valve without first determining the cause of the fault condition. Use the appropriate fault code troubleshooting tree in Section TF, in the Fault Code Troubleshooting Manual, Bulletin 4022225.

Begin cranking the engine until fuel exits the drain line.

When fuel begins to exit the drain line, route the drain flow to a graduated cylinder and continue cranking for 60 seconds.

NOTE: Do not crank the engine for 30 seconds continously. Crank the engine in 15 second intervals with a 15 second pause between intervals. This reduces the possibility of overheating the starting motor.

The leakage should be less than 10 drops per minute.

Refer to the appropriate troubleshooting symptom tree for repair directions.

NOTE: If Fault Code 449 or 2311 is active, do not replace the fuel pressure relief valve without first determining the cause of the fault condition. Use the appropriate fault code troubleshooting tree in Section TF, in the Fault Code Troubleshooting Manual, Bulletin 4022225.