Due to the design limitations of the PD fuel system the engine control unit has 5 calibration maps for the injectors and the one that is used is dependent on the current start of injection point.
This is because the fuel delivery pressure is dependent on start of injection point due to the injector being driven by a cam load to generate pressure
The maps have reference engine speed against injection quantity to determine an opening time for the injectors in degrees of crankshaft rotation.
The start of injection has ten main maps that are selected via coolant temperature and again use engine speed and injection quantity to determine the start of injection point
There are lots of corrections to these maps and the fuel temperature is one of them.
Due to the fuel density being lower at higher liquid temperature it is necessary for the injector to be held open longer to get the same mass of fuel delivered.
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