Start of Injection (SOI) timing determines when fuel enters the combustion chamber relative to piston position. SOI directly affects power output, emissions, combustion noise and mechanical stress on the engine.

Visión general

The ECU calculates optimal injection timing based on RPM, load, temperature and rail pressure. Earlier injection increases power but raises NOx and combustion noise; later injection reduces NOx but increases soot.

Controlled Signals

• Crankshaft position
• Camshaft position
• Rail pressure
• Temperatura del aire de admisión
• Coolant temperature

Maps Involved

• Main SOI Maps vs RPM/IQ
• Temperature Correction Maps
• Altitude Correction Maps
• Pilot Injection Timing Maps

Logic Sequence

IQ Request → Base SOI Lookup
         ↓
Temperature / Pressure Corrections
         ↓
Final SOI Command → Injector Driver

Calibration Objectives

• Optimize power delivery
• Control combustion noise
• Balance NOx vs soot trade-off

Calibration Strategy

• Advance SOI moderately for more power (1-3° max)
• Monitor cylinder pressure rise rate
• Coordinate with pilot injection timing
• Verify EGT remains within limits

Diagnóstico

• Injection timing deviation faults
• Excessive combustion noise complaints
• High NOx readings during emissions test

Best Practices

• Small SOI changes have large effects — move in 0.5° increments
• Always verify cold start behavior after SOI changes