* Air Inlet Restriction
* Exhaust Restriction
* Fuel System Leaks
* Low Quality Fuel
* Defect In Turbocharger
* Fuel And Combustion Noise (Knock)
* Defect In Unit Injector(s)
* Improper Speed/Timing Calibration
* Improper Vehicle Operation
1. Air inlet restriction:
Restriction of the air coming into the engine can cause high cylinder temperatures and more than normal amount of heat to pass to the cooling system. Check for restriction with a water manometer or a vacuum gauge (which measures in inches of water). Connect the gauge to the engine air inlet between the air cleaner and the inlet to the turbocharger. With the gauge installed, run the engine at full load rpm and check the restriction. Maximum restriction of the air inlet is 6.22 kPa (25 inches of water). If the indication is higher than maximum permissible restriction, remove the foreign material from the filter element, or install a new filter element and check for the restriction again. If the indication is still too high, there must be a restriction in the inlet piping.
2. Exhaust restriction:
Restriction in the exhaust system can cause high cylinder temperatures and more than normal amount of heat to pass to the cooling system. To check if there is an exhaust restriction, make a visual inspection of the exhaust system. Check for damage to piping or for a defective muffler. If no damage is found, check the exhaust system for back pressure from the exhaust (pressure difference measurement between exhaust outlet and atmosphere). The back pressure must not be more than 10.0 kPa (40 inches of water). Check the system by removing the exhaust pipes from the exhaust manifolds. With the exhaust pipes removed, start and run the engine to see if the problem is corrected.
3. Fuel system leaks:
a. Check fuel system for any external leaks. Check all lines, hoses, and fittings for leaks and tighten or replace as necessary.
b. Check for a defective O-ring seal on the top of the unit injector. Remove the fuel supply line at the front of the cylinder head and pressurize the cylinder head (the return to fuel tank line will have to be blocked). Look for fuel leaking from the unit injectors where they seal with the cylinder head. If fuel is leaking from the unit injector, remove the unit injector and replace the upper O-ring seal. Also depending on the amount of leakage an oil sample should be taken and checked for fuel dilution. Change oil and oil filter if necessary. While the cylinder head is pressurized, check for porosity around the oil drain back holes. If porosity is found, replace the cylinder head. If fuel is found in the coolant, then check the unit injector sleeves in the cylinder head for cracks or erosion. If defects are found, then remove the sleeves and install new sleeves.
NOTE: Refer to Disassembly And Assembly, SENR6553, for the proper procedure for unit injector removal and installation.
4. Low quality fuel:
Test the engine with fuel according to recommendations by Caterpillar Inc. Refer to Truck Performance And Driveability Diagnostic Guide, LEBT3477.
5. Defect in Turbocharger:
Check to see if turbocharger spins freely. Repair as needed or install new components.
6. Fuel and combustion noise (knock):
See Problem No. 4, Engine Misfiring or Running Rough. See Problem No. 9, Loud Combustion Noise.
7. Defect in unit injector(s):
Using an electronic service tool check for logged or active diagnostic codes. Refer to 3100 HEUI Diesel Truck Engine Electronic Troubleshooting SENR6566, for Injector Solenoid Circuit Test.
8. Improper speed/timing calibration:
Using an electronic service tool check for logged or active diagnostic codes. Refer to 3100 HEUI Diesel Truck Engine Electronic Troubleshooting SENR6566, for Engine Speed/Timing Calibration.
9. Improper vehicle operation:
Using an electronic service tool check for logged or active diagnostic codes. Refer to 3100 HEUI Diesel Truck Engine Electronic Troubleshooting SENR6566, Poor Fuel Consumption.