CONFIDENTIAL TIBU4189-01

There have been some complaints of engine stumble/misfire on acceleration when the engine rpm is between 1400 and 2000 rpm on the C7 On-highway Truck Engines.

Some checks must be performed in order to determine the root cause before any component replacements.

1. Diagnostic Codes - Review any diagnostic codes and resolve any active diagnostic codes that are present.
2. Update flash file - For High horsepower engines (250HP to 330HP) with original 233-3535 factory installed injectors, install service Flash file dated "APR04" (see table 1). These files were released to address "engine stumble". Ensure that the correct flash file is installed for the injector part number for the engine. Refer to the flash file reference "readxref.txt" in SIS to determine which flash file is correct based on injector part number installed in the engine, horsepower/torque rating, and the engine serial number.
3. Perform "Cylinder Cutout Test" on Caterpillar Electronic Technician. Take appropriate action based on the results of the test. If the test results are "questionable", the technician must verify that the injector trim file is correct for that injector that is installed in the engine. (Select the "Create Report" button from the bottom of the Cylinder Test screen).

• Correct Injector Trim File (ETRIM) - An incorrect injector trim file can cause the engine to run improperly. See step 3 Perform "Cylinder Cutout Test".
• Perform HEUI "Injection Actuation Pressure Test" - The electronic troubleshooting guide outlines this test. The test will identify if the HEUI system is causing the engine hesitation (HEUI system malfunction can also include symptom of hard starting and rough idle).
• Check the Camshaft Speed/Timing Sensor Air Gap (see additional symptom requirements) ? If the engine stumbling is combined with intermittent hard starting the technician needs to verify that the camshaft gear to Speed/Timing sensor air gap is not excessive. (Specification 0.040" +/- 0.020")
• Check for Air in Fuel (See additional symptom requirements) ? If the engine stumble is constant and does not cleanup under steady rpm conditions, the technician needs to ensure that the low-pressure fuel system is not being aerated. You can make this check by installing a sight tube in the inlet passages and outlet passages of the cylinder head. Issues that can affect the low pressure fuel system and engine operation include fuel filter plugging, air leaking into the suction side of the system, fuel priming pump, plugged fuel return line, combustion gas, and etc.

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