Common-rail pressure control ensures precise fuel atomization and engine efficiency across the full operating range. EDC17/MG1 ECUs use multi-loop control to regulate pressure based on driver torque demand and protection limits.
Overview
The ECU computes target rail pressure from torque request, air mass, temperature and injection timing, then actuates the IMV/DRV to reach the target.
Controlled Signals
- Rail pressure sensor (feedback)
- IMV/DRV duty cycle
- Fuel temperature
- Torque request pathways
Maps Involved
- Rail Pressure Target vs RPM/torque
- Pressure Limiter (absolute safety cap)
- Temperature Compensation Maps
- Startup Pressure Maps
Logic Sequence
Torque Model → IQ Request → Rail Pressure Target
↓
Check Limiters / Temperature
↓
Closed-loop control via IMV/DRV
↓
Stabilization & Monitoring
Calibration Objectives
- Ensure stable injection quantity
- Prevent pump overload
- Minimize noise and emissions
Calibration Strategy
- Do not raise pressure limiters before correcting torque model
- Increase target pressure moderately for higher torque, avoiding pump saturation
- Adjust temperature maps if fuel viscosity changes
Diagnostics
- Rail deviation positive/negative
- P0087 / P0088 pressure faults
- IMV sticking or low supply pressure
Best Practices
- Stability is more important than peak pressure
- Watch pump duty over 65–70%