Ignition Angle Setting, Basic Function - GF07.10-P-1046A

Engine 139, 176, 177, 254, 256, 260, 264, 274, 279, 282 

Engine 177, 256 

Overview 

This document contains information on:

• General 
• Function 

General 

If the engine knocks, the knock control corrects the ignition angle for each cylinder using the ignition angle setting. For this purpose, the combustion engine control unit calculates a cylinder-specific ignition angle correction in accordance with its input signals.

The ignition angle influences the time at which the fuel/air mixture ignites in the combustion chamber. The ignition angle refers to the top dead center (TDC) of the power stroke of the crankshaft of the engine. If the ignition angle is adjusted to "early," it is far ahead of TDC. If the ignition angle is adjusted to "retarded", it is closer to, but still ahead of, TDC.

Function 

The following sensors are used for detecting the ignition angle:

• Pressure sensors downstream of the throttle valve
• Camshaft Hall sensors
• Knock sensors
• Coolant temperature sensor
• Crankshaft Hall sensors
• Charge air temperature sensors

If the knock control detects knocking at a cylinder via the knock sensors, the cylinder's ignition angle is adjusted to "retarded" starting with the next ignition. The ignition angle is adjusted depending on the engine speed and the engine load. If the engine still knocks, the ignition angle is adjusted to "retarded" until the maximum adjustment is reached.

If knocking-free combustion occurs, after several ignitions the ignition angle is adjusted step-by-step to "early" until the normal characteristics map value is reached again or until the engine knocks again.