The amount of fuel injected is proportional to the injector duration (opening time), fuel rail pressure, fuel temperature and fluid
A target value for injector duration under specific conditions is programmed into the control unit (ECU) engine control map.
The fuel injectors are machined to very fine tolerances but because of individual characteristics such as friction, pressure drop, magnetic force, wear during service etc, very slight variations in flow can occur.
Slight difference between target flow and actual flow can occur due to high operating pressures.
Certain common rail diesel fuel injectors require calibration during manufacture or overhaul on a specialised diesel injection test rig to produce a data code relating to the characteristics of each individual injector. This data code may be referred.
to as the C2i code, IMA/IQA code or QR code depending on manufacturer.
The data code is programmed into the engine control unit identifying to which cylinder the injector is fitted.
This data code allows the engine control module to correct the pulse duration applied to each individual injector to maintain optimum performance. Fitment of replacement injectors will require the
new injectors to be coded to the engine control unit.
Injector coding classification type
Some earlier common rail injectors have no coding. And some Bosch and some Siemens/VDO injectors use a single code identification process for injectors called injector classification. This is a single digit code and for example, a 2008 Ford Mondeo could have injectors fitted that are class 6 or class 5. So, if you replaced the injectors and you are fitting a different class you need to tell the ECU this.
This is basically telling the ECU the type of injector you have fitted and the code will be the same for all 4 injectors (the code is not unique to each injector like the IMA/IQA/QR codes).
This code will normally be marked on the top of the injector.
Some earlier Denso injectors do not have coding or classification. Instead, they have 2 extra pins on the injector and inside the is a resistor that has a value that matches the manufacturing tolerances of the injector.
Normally the letter O is not used for the code so if you see something that looks like a O it is a number 0.
As well as coding injectors now some vehicles may require a pilot injection learning done when the injectors are replaced or if the engine starts to get a diesel knock. Some vehicles will do this automatically and in some cases it will have to be done with the diagnostic tool.
On some vehicles it is also necessary to relearn the pressure control valve learned values when you replace injectors.