Common Rail is the injection technology that has revolutionized modern diesels. A high pressure pump (HPP) accumulates fuel in a common "rail" (1500-2500 bar), from which the injectors take the fuel to spray it into the cylinder with multiple injections per cycle.
Advantages
- Multiple injections/cycle (pilot, pre, main, post)
- Constant pressure regardless of engine speed
- More power, less consumption, less noise vs the old ones injector pump
Key components
- HPP (High Pressure Pump): generates pressure
- Rail: common high pressure tank
- Injectors: solenoid (Bosch CRI1-CRI3) or piezoelectric (Bosch CRI3.20)
- Pressure sensor rail: feedback to the ECU
- Pressure regulation valve: ZME/MPROP
Common Rail Tuning
The chiptuning on CR mainly modifies rail pressure (for more power), injection duration (more fuel) and SOI advance (Start Of Injection, to optimize combustion).
High operation pressure
The high pressure pump keeps the rail at a regulated pressure independent of the speed, while a valve (ZME/MPROP or rail-side regulator) precisely doses the value required by the ECU. The injectors, electrically controlled, perform up to five-seven injections per cycle (pilot, pre, main, post) to optimize noise, emissions and power.
Reliability in tuning
In chiptuning, the increase in rail pressure and injection duration must be measured: beyond the factory limits, the pump and injectors are stressed, in particular the Bosch CP4 pumps known for their fragility. A breakage of the CP4 contaminates the entire circuit (rails, injectors, pipes) with very high restoration costs. For this reason, a conservative Stage 1 remains within limited increments, reserving the higher values for the stages with adequate hardware.
Maintenance
The Common Rail is sensitive to the quality of the diesel: water and impurities ruin the high-precision pump and injectors. A fuel filter in order and clean diesel fuel are the first form of prevention, especially on remapped engines that work at high pressures. In diagnosis, the comparison between the requested and measured rail pressure and the correction values of the individual injectors is the quickest way to identify a component that is running out.