G4 Wiring and Installation Manual
60
© 2009 Link
11.5
Essential Tuning Adjustments
It is assumed that at this stage all set-up procedures described in previous sections have
been completed and the engine is running. The following steps detail correct set-up
procedures for some of the more critical ECU parameters (note that MAP Sensor Calibration
should have already been completed by now):
MAP Sensor Calibration
At key on and engine not running the Manifold Absolute Pressure (MAP) Sensor should
always match the Barometric Absolute Pressure (BAP) Sensor. As well as providing altitude
correction, the BAP sensor also allows the MAP sensor to be calibrated prior to tuning.
G4 ECUs use an on-board barometric sensor that is calibrated prior to dispatch. This
ensures that all PCLink Tuning Software programs (PCL Files) give a consistent state of
tune throughout the ECU range. This allows a PCL file to be transferred between G4 based
ECU's giving an equivalent state of tune providing all factors affecting VE are equal.
Without the ability to calibrate all the available types of MAP Sensors to the BAP Sensor
there would be significant affects on the accuracy of the resulting tune, especially when
tuning with Manifold Gauge Pressure (MGP) as a load index.
To calibrate the MAP sensor, select the 'MAP Sensor Calibration' item in the PCLink Tuning
Software 'Options' menu and follow on screen instructions.
Injector Voltage (Dead time) Correction
There is always a delay between the injector being energised and the injector actually
opening. Likewise, there is a small delay between the injector being de-energised and the
injector closing. The opening time is considerably longer than the closing time, however the
overall result is that less fuel will flow for a given pulse width than would be expected with an
'ideal injector'. To compensate for this the injector pulse widths are increased to
compensate for this 'dead-time'. The dead-time for a given injector is a function of the
battery voltage, differential fuel pressure and the type of injector driver (saturated or peak
and hold). A typical dead-time at 3 Bar differential fuel pressure and 14 volts is just under
1ms (ms = millisecond = 1 thousandth of a second).
In applications with a linear 1:1 fuel pressure regulator (i.e. not a rising rate regulator), the
differential fuel pressure (difference between manifold pressure and fuel pressure) will be
constant. Therefore the only variable that is changing will be the battery voltage (this
changes with electrical load and sometimes engine speed). Without correction, the changes
in dead time will cause the engine to run lean when the voltage drops. If the Injector Voltage
Correction is properly set-up then changes in the battery voltage will not affect the air/fuel
ratio.
The injector dead-time table allows the dead- time for different battery voltages to be
entered. The values represent the dead-time in milliseconds. These should increase with
falling system voltage.
Injector dead time for a particular set of injectors can be determined using a flow bench or
on a running engine.
To determine the injector dead-time using a flow bench, the injectors need to be operated at
the intended operating pressure (normally three bar) and at a constant duty cycle as well as
a set voltage. Vary the supply voltage to the injector and measure minimum pulse width at
which the injectors will flow for a particular voltage. This is the required dead-time for that
injector at that tested voltage.
To determine injector dead time on a running engine, with the engine fully warmed and