Post injection delivers additional fuel after the main combustion event. Its primary purposes are supporting DPF active regeneration (by raising exhaust temperature) and reducing hydrocarbon emissions during engine warm-up.

Panoramica

The ECU commands post injection when exhaust temperature needs to increase, typically for DPF regeneration or catalyst light-off. The fuel burns in the exhaust manifold or oxidation catalyst, not in the cylinder.

Controlled Signals

• Post injection quantity
• Post injection timing (°ATDC)
• Exhaust gas temperature
• DPF soot load estimation

Maps Involved

• Post Injection Quantity Maps
• Post Injection Timing Maps
• DPF Regeneration Request Maps
• EGT Target Maps

Logic Sequence

DPF Regen Request OR Warm-up Mode
         ↓
Post Injection Enable
         ↓
Quantity & Timing Calculation
         ↓
EGT Feedback Control

Calibration Objectives

• Achieve target EGT for DPF regeneration
• Minimize fuel dilution in engine oil
• Prevent injector coking

Calibration Strategy

• Post injection is emissions-critical — modify with caution
• If DPF is removed, post injection can be disabled
• Monitor oil dilution on high-mileage vehicles

Diagnostica

• DPF regeneration incomplete
• Oil level rise (fuel dilution)
• EGT sensor faults

Best Practices

• Never disable post injection on DPF-equipped vehicles unless DPF is removed
• Check oil condition regularly on tuned vehicles