- Excessive load
- Excessive inlet manifold air pressure
- High inlet air temperature
- Incorrect air/fuel ratio
- Incorrect base timing
- The engine speed/timing sensor is not calibrated.
- Faulty circuit for the detonation sensor(s)
- Excessive deposits in the combustion chamber
Make sure that the load is not excessive. Reduce the load. If necessary, disengage the driven equipment and test the engine.
Check the Inlet Manifold Air Pressure
The calculated engine load increases when the inlet manifold air pressure increases. Measure the inlet manifold air pressure during engine operation with a load. For specific data on the engine, refer to the engine Technical Marketing Information.
Check the Inlet Air Temperature
High inlet air temperature can cause detonation. Check the inlet air temperature.
Refer to Troubleshooting, "Inlet Air Temperature (High)".
An air/fuel mixture that is too rich will cause detonation. Verify that the exhaust emissions are correct. Refer to Operation and Maintenance Manual, "Carburetor Air/Fuel Ratio - Check/Adjust".
A change in the fuel energy content will change the air/fuel ratio. Obtain a fuel analysis.
The fuel supply pressure must be adequate and stable.
Make sure that the fuel metering valve is operating correctly.
Verify that the base timing is correct. Refer to Operation and Maintenance Manual, "Ignition Timing - Check/Adjust".
Calibrate the Engine Speed/Timing Sensor
Note: Only perform this procedure if work on the engine may have affected the engine timing. Also, perform this procedure if the engine speed/timing sensor has not been calibrated.
Calibrate the engine speed/timing sensor. Refer to Troubleshooting, "Engine Speed/Timing Sensor - Calibrate".
Troubleshoot the detonation sensors. Refer to Troubleshooting, "Detonation Sensors".
Check for Deposits in the Cylinders
Overfilling of engine oil can lead to deposits. Make sure that the engine oil level is correct.
Note: Excessive deposits contribute to guttering of the valves.
Use a borescope to inspect the cylinders. Look for the following conditions:
- Deposits on the valve seats
- Deposits on the valve faces
- Deposits on the cylinder walls that are above the upper limit of the piston stroke
- Signs of internal leaks
Signs of internal leaks include excessive consumption of engine oil, blue smoke, and excessive detonation.
If excessive deposits and/or signs of internal leaks are found, investigate the cause of the condition. Make repairs, as needed.