#How chip tuning works in the common rail engine

28 / February 2022
How chip tuning works in the common rail engine

Seletron Performance

How chip tuning additional units for common-rail engines work


The common-rail diesel: an all Italian design

First of all, we should thank Italian engineer Mario Ricco for having this excellent insight. It was this engineer that invented the common-rail system in Italy. It happened in the early 1990s, but to see the first cars with this modern injection system on the road, we had to wait until 1997, when the Alfa 156 1.9JTD and the Mercedes C-Class with the 220CDI were put on the market. 

The former was fitted with the first 4-cylinder 1900 with two valves per cylinder, a single overhead camshaft, fixed-geometry turbocharger with intercooler, and delivered 105hp. The Mercedes, on the other hand, used the first 4-cylinder 2200 with 125hp power employed on the C-Class.

Both engines employed this new injection system engineered and manufactured by Bosch, which had at least two advantages over previous injection systems. These were the injection pressure (Bosch's first-generation common-rail reached peaks of 1350 bar) and, for the first time, absolute independence between piston position and the ability to generate multiple injections. This was achieved because, for the first time, diesel fuel was pressurized and then stored inside a tank (the rail).

Each electroinjector (initially electromagnetic) delivers the diesel and the pressure through metal ducts, and the ECU drives the valve needle opening through PWM control of the solenoid contained within the injector.

To generate the diesel pressure of about 1350 bar, the system uses a triple radial piston pump driven by the timing belt. A pressure modulator controlled by the ECU is mounted on the injection pump or flute (the rail), which acts as a by-pass when the pressure, set by the ECU's internal maps and detected through the common-rail pressure sensor, is exceeded. Each electro-injector can thus have diesel fuel at a stable pressure and independent of engine speed.

This configuration allows for multiple, precise injections that optimize engine operation throughout the rev range. In later years, other manufacturers of common-rail diesel units used systems that were quite similar in operation but employed a spherical reservoir instead of the "flute" used in the Bosch system (e.g., Ford on the 1.4 tdci and the 1.8tdci). Years later, all manufacturers aligned in this respect, preferring the linear reservoir.


From the point of view of electronic management, there are no distinct differences between injector-pump systems. On common-rails, the values of inlet air mass (through the MAF sensor), inlet air temperature (through the MAF sensor or separately), diesel temperature, engine speed, engine phase, engine coolant temperature, accelerator pedal position, boost pressure (through the MAP sensor), and diesel injection pressure (through the RAIL sensor) are also detected. The ECU controls the triggering of the EGR (exhaust gas recirculation) valve, the injection pressure (through the rail pressure modulator), and the opening of each individual electro-injector through its outputs.

We started developing our chip tuning for common-rail injection systems back in the late 1990s. Even today, after appropriate adaptations, many of our additional chip tuning modules for enhancing diesels still use a dual control system that mainly acts on two parameters: diesel injection pressure and boost pressure for the more recent ones that also control the engine speed (RPM)

Among the earliest users of the Bosch-engineered common rail system is BMW, which introduced the world's (then) most powerful 3000 Diesel 6-cylinder inline car diesel. It had 184 horsepower and 390Nm of engine torque, normal values today for a 2-liter 4-cylinder but a record for the late 1990s! The engine appeared on the E39 5 Series named 530d and was increased shortly thereafter to 193 horsepower and 410Nm of maximum torque. On BMW 530d, we installed many additional chip tuning modules capable of generating high power and torque gains. These digital kits (like all those we have produced since the early days) were very popular both in Italy and in Europe.

Early chip tuning units for common-rails required connecting some wires on the engine harness, specifically two wires on the rail pressure sensor, two wires on the turbo pressure sensor, one wire on the accelerator pedal position sensor, and any ground and 12V positive connections. This made the chip tuning suitable primarily for installers such as mechanics, electricians, and car tuning.

In the early 2000s, the original connectors arrived, making chip tuning additional units much more attractive even to private individuals who, with basic manual dexterity and no special experience, can install the engine enhancement units themselves on their cars without having to go to a professional in the field, just as is the case today with newer models.


Common-rails with piezoelectric electro-injectors

As was the case with the injector-pump unit systems, there have been developments in the common-rail electric-injector opening control system. First of all, remember that the electric control does not function as an ordinary valve that directly opens and closes the flow of pressurized diesel fuel.

In fact, remember that the first common-rail systems worked with pressures of 1350 bar, then were raised to pressures of 1600 bar in later generations. They eventually reached the threshold of 2000 bar, and from this point, it becomes very difficult to switch a nozzle with this counterthrust. The electro-injectors work on the pressure imbalance (thus on the pressure difference) that causes the injector plug itself to open up.

Early common-rail injectors (and some current models as well) used electromagnetic controls to control these openings. The ECU sends voltage (current) to solenoids (copper windings) located inside the injectors, and these act via electromagnetic force on ferromagnetic elements that move, creating precisely the diesel pressure imbalance. This imbalance will lead to the opening and thus to the pulverization of the diesel.

In some common-rail systems (widely used today), control elements are used that are no longer electromagnetic but have a piezoelectric effect ( remember the crystals that can change their physical state when stressed by a difference in electrical voltage?).

Since the control requirements are different from those of electromagnetic injectors, the ECUs also had to undergo partial redesigns due to different voltage and current values in the operation of piezoelectric electro-injectors. As a result, we at SELETRON also had to develop new versions of our chip tuning for upgrading common-rail turbodiesels in order to create an electrical interface suitable for tuning engines that use these advanced diesel injection systems.


Further development of the diesel common-rail

Some turbo diesel engine manufacturers have gone even further in diesel injection unit technology. Volvo, for example, has employed a new type of common-rail injectors that are more complex but more precise in handling the various stages of diesel injection.

These complex injectors communicate with the ECU through the data BUS and also provide diesel temperature information. Specifically, the Volvo V40 2.0 Diesel 120 hp is equipped with a system called i-ART, the intelligent diesel injection system created by Denso and used in Volvo and Toyota engines that uses one pressure sensor and one temperature sensor for each individual common-rail injector.

This system provides even more accurate and targeted dosing for each individual injection stage, benefiting emissions, performance, and diesel consumption. Again, we had to completely redesign a complex chip tuning unit capable of connecting to each individual electro-injector, reading its stock values, and steering them to create an interesting performance boost. Our CHIPBOX kit (one of the few available for these advanced i-ART injection systems) is complete with all wiring harnesses featuring genuine connectors for each individual injector. Once again, we'll mention that our chip tuning are reversible anytime and are capable of generating excellent power and torque gains of +30 hp and +60Nm!

To sum up, in previous articles (which we suggest you read because they are very interesting), we have talked about:

- How electronically controlled rotary injection pumps work and chip tuning additional units for increased power and torque of TDI and tds engines and other cars using this injection system.

- How radial piston injection pumps with electronic control work installed on earlier VW-Audi group 2500TDI V6 engines, BMW 2-liter 16V 136hp, Ford 1.8tddi, and other 2000 Opel engines, and how the chip tuning work to increase power and torque.

How the PDE injector pump system works used initially only by the VW-Audi group, how the injectors developed from electromagnetic to piezoelectric control, and again how the chip tuning additional units work to increase the power and torque of these TDIs.

- We have now completed this technical section covering the latest and most refined diesel injection systems, common-rails, and how this system has evolved over time. Finally, we also discussed how chip tuning units work for increasing the power and torque and how they have developed around the needs of the latest technology.

In the next articles, as requested by some of our customers (remember that these articles were also chosen by a survey we submitted to those who follow us regularly), we will also talk about chip tuning for gasoline-powered engines and accelerator pedal chip tuning modules.

You'll just have to follow us! See you soon



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