CROWN 8J6166 - Caterpillar

Air/Fuel Ratio
The correct air/fuel ratio is very important for the following considerations:
Margin of detonation
Control of emissions
Achieving optimum service life for the engineIf the air/fuel ratio is not appropriate for the fuel and the operating conditions, a failure of the engine may occur. The service life of the turbocharger, the valves, and other components may be reduced.Fuel Supply Pressure
Fluctuations of the fuel pressure can change the air/fuel ratio. The maximum fluctuation that is allowed in the fuel pressure is 3.4 kPa (0.50 psi). Ensure a stable fuel pressure to the engine by installing a second gas pressure regulator prior to the gas pressure regulator on the engine.Table 1 lists the fuel pressure that is required for the gas pressure regulator.
Table 1
Requirements for Fuel Pressure To the Gas Pressure Regulator    
Fuel System     Pressure    
Low pressure gas     10.3 to 34 2 kPa
1.50 to 5 0.25 psi    
High pressure gas     172 to 207 7 kPa
25 to 30 1 psi    Gas Pressure Regulator
The gas pressure regulator maintains a pressure differential between the air and the fuel that is supplied to the carburetor. Set the pressure of the fuel supply to a maximum of 1 to 1.2 kPa (4 to 4.5 inches of H2O) higher than the pressure of the air supply. The gas pressure regulator will maintain the pressure differential in response to changes in the air pressure, if the gas pressure regulator is installed properly.A water manometer is used to measure the pressure differential. This measurement is taken when the engine is operating at high idle rpm. After a load is applied, the fuel pressure will usually decrease by approximately 0.1 to 0.25 kPa (0.50 to 1 inches of H2O). If the performance of the gas pressure regulator is erratic, the gas pressure regulator may require service.Temperature of the Fuel Supply
Changes in the temperature of the fuel supply affects the air/fuel ratio. Warmer fuel is less dense than cold fuel. This results in a leaner mixture that causes a noticeable reduction of power.Temperature of the Air Supply
Changes in the temperature of the air supply affects the air/fuel ratio. In addition to seasonal changes, the air temperature changes overnight. Control of the temperature in the engine room will help to maintain the air/fuel ratio.To optimize the inlet air temperature, use ducting and a heat exchanger. This will help to avoid exposure to hot air from a generator. For more information, refer to Application and Installation Guide, LEKQ7250, "Air Intake". Consult your Caterpillar dealer for assistance.Angle of the Throttle Plate
On turbocharged engines, the angle of the throttle plate is adjusted for full load operation. The angle is adjusted by changing the setting of the exhaust bypass valve, if equipped. The proper angle at full load is 70 degrees.The following factors affect the angle of the throttle:
LHV of the fuel
Setting of the air/fuel ratio (inlet manifold air pressure)
Setting of the exhaust bypass (if equipped)
AltitudeEnsure that the angle of the throttle plate is properly