Low Pressure Fuel System

1. Visually check the fuel level. Do not rely on the fuel gauge only. If necessary, add fuel. If the engine has been run out of fuel, purge the air from the fuel system. Prime the fuel system.

2. Ensure that the fuel supply valve (if equipped) is in the full OPEN position.

Contact with high pressure fuel may cause fluid penetration and burn hazards. High pressure fuel spray may cause a fire hazard. Failure to follow these inspection, maintenance and service instructions may cause personal injury or death

Do not loosen any high pressure fuel lines when the engine is running. The high pressure in the fuel lines can cause personal injury or death. Wait 60 seconds after the engine has stopped to allow pressure to purge before any service or repair is performed on the engine fuel lines.



3. Check the fuel lines for the following problems: restrictions, collapsed lines, pinched lines and loose connections. If problems are found with the low-pressure fuel lines, repair the lines and/or replace the lines. If the high-pressure fuel lines have a leak, the high-pressure fuel lines must be replaced. Refer to the Disassembly and Assembly manual.

NOTICE Do not crank the engine continuously for more than 30 seconds. Allow the starting motor to cool for two minutes before cranking the engine again.

4. Prime the fuel system if any of the following procedures have been performed:

o Replacement of the fuel filters

o Service on the low-pressure fuel supply circuit

o Replacement of unit injectors

Note: A sight glass in the low-pressure supply line is helpful in diagnosing air in the fuel. Refer to Testing and Adjusting.

5. Check for air in the fuel system. Refer to Testing and Adjusting, "Air in Fuel - Test". Ensure that the fuel system has been primed. Attempt to start the engine. If the engine will not start, continue with this procedure.

6. Check the fuel tank for foreign objects which may block the fuel supply.

7. Check the fuel filters.

8. Check the diesel fuel for contamination. For acceptable quality, refer to Operation and Maintenance Manual.

9. Cold weather adversely affects the characteristics of the fuel. Refer to the Operation and Maintenance Manual for information on improving the characteristics of the fuel during cold-weather operation.

10. Attempt to start the engine. If the engine will not start, continue with this procedure.

11. Check the flow of fuel through the transfer pump. If the flow is less than 250 mL (8.5 oz) per minute at 150 rpm, replace the pump. For instructions on removal and installation of the fuel transfer pump, refer to the engine Disassembly and Assembly manual. Make sure that the engine is primed. Attempt to start the engine. If the engine will not start, continue with this procedure.

High Pressure Fuel System

Escaping fluid under pressure, even a pinhole size leak, can penetrate body tissue, causing serious injury, and possible death. If fluid is injected into your skin, it must be treated immediately by a doctor familiar with this type of injury.

Always use a board or cardboard when checking for a leak.

Do not loosen any high pressure fuel lines when the engine is running. The high pressure in the fuel lines can cause personal injury or death. Wait 60 seconds after the engine has stopped to allow pressure to purge before any service or repair is performed on the engine fuel lines.



1. Use Cat ET to check the absolute fuel rail pressure while the engine is cranking at a minimum speed of 150 rpm.

2. If the absolute fuel rail pressure is less than 25 MPa (3626 psi), perform the following procedure.

a. Check for fuel leaks in the high-pressure fuel system. Rectify any fuel leaks and then recheck the pressure in the fuel rail. If the absolute fuel rail pressure is greater than 25 MPa (3626 psi), proceed to Test Step 3.

b. Check that the inlet pressure at the fuel rail pump is greater than 50 kPa (7 psi). If the inlet pressure is less than 50 kPa (7 psi), repeat the diagnostic process from "Fuel Supply".

c. Use Cat ET to perform a solenoid test on the fuel rail pump. Refer to Troubleshooting, "Fuel Rail Pump - Test". Make repairs, as needed.

d. Attempt to start the engine. If the engine will not start, continue with this procedure.

e. Check the pressure relief valve in the fuel rail for leakage. If the pressure relief valve is leaking, replace the valve and recheck the pressure in the fuel rail.

f. If the pressure relief valve in the fuel rail is not leaking, check for fuel in the engine oil system. If fuel is suspected in the oil system, take an engine oil sample for analysis. Refer to the Operation and Maintenance Manual, "Engine Oil Sample - Obtain". If the analysis confirms that there is fuel in the engine oil system, investigate the cause.

g. If the absolute fuel rail pressure is less than 25 MPa (3625 psi), remove the outlet check valves from the pump. Clean the check valves and reinstall the check valves.

h. If no fuel is found in the oil system and the outlet check valves are OK, check for excessive fuel leak off from the injectors.

Note: The fault is not in the fuel rail pump. Do not replace the pump.

i. If the leak off is greater than the following quantity, replace the electronic unit injectors.

§ 38 mL (1.3 oz) in 30 seconds for a 6 cylinder engine

§ 25 mL (0.85 oz) in 30 seconds for a 4 cylinder engine

Note: Discard all fuel injection lines after use. Fuel injection lines must only be used one time.

j. If the leak off is less than the following quantity, proceed to Test Step 2.k.

§ 38 mL (1.3 oz) in 30 seconds for a 6 cylinder engine

§ 25 mL (0.85 oz) in 30 seconds for a 4 cylinder engine

k. Check the timing of the fuel rail pump. Refer to Testing and Adjusting, "Fuel Injection Timing - Check".

l. If the timing of the fuel rail pump required adjustment and the engine will not start, return to Test Step 1.

m. If the timing of the fuel rail pump was correct, replace the fuel rail pump. If the engine will not start, return to Test Step 1.

3. If the absolute fuel rail pressure is greater than 25 MPa (3626 psi), perform the following procedure.

a. Use Cat ET to make sure that the status of the electronic unit injectors is not "Disabled". If the injectors are disabled but not intentionally disabled with Cat ET, continue to Test Step 3.b.

b. If the electronic unit injectors are not disabled, use Cat ET to perform an injector solenoid test. Refer to Troubleshooting, "Injector Solenoid - Test".

c. If any service has been performed as a result of Step 3.b, attempt to start the engine. If the engine will not start, proceed to 3.d.

d. Contact the technical communicator at the Caterpillar dealer.

Note: This consultation can greatly reduce the repair time.

e. If the technical communicator recommends the use of a test ECM, install a test ECM. Refer to Troubleshooting, "Test ECM Mode".

f. If the engine starts normally, replace the ECM.

Cylinder Performance

1. Perform a compression test. Refer to Systems Operation/Testing and Adjusting. Possible causes of low compression are shown in the following list:

o Faulty piston

o Faulty piston rings

o Worn cylinder bores

o Worn valves

o Faulty cylinder head gasket

o Damaged cylinder head