Engine Diagnosis - Mechanical

ENGINE DIAGNOSIS - MECHANICAL










OFF-IDLE ENGINE SPEED LOW DURING COLD START

Dependent upon engine coolant temperature, the Engine Control Module (ECM) will temporarily delay (limit) the maximum engine speed when the vehicle is not moving. For automatic transmission equipped vehicles, the maximum engine speed is temporarily delayed when the vehicle speed is less than one mph, and when the transmission selector is in either the neutral or park position. For manual transmission equipped vehicles, the maximum engine speed is temporarily delayed when the vehicle speed is less than one mph. This ECM feature is used to protect the engine turbocharger. By temporarily limiting the engine speed, the shaft speed of the engine turbocharger is controlled to a low speed. This delay in maximum engine and turbocharger shaft speed allows for sufficient oil lubrication to the turbocharger shaft bearings. Satisfactory oil lubrication of the turbocharger shaft bearings is important for long term turbocharger durability. The 6.7L engine speed is temporarily limited to 1,200 RPM's when the above conditions are met. The length of time that the maximum engine speed is temporarily limited is dependent upon engine coolant temperature. Refer to the table to determine the amount of Time Delay.

NOTE: The time delay values supplied in the table are an approximation and may vary per application.