Dodge Cummins User Guide
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8. Save changes to the tune file by using the Save tuning file, Save tuning file as,
or Save tuning file for AutoCal options.
If using the Save option, ensure you have a copy of your stock tune saved
elsewhere.
Save tuning file as, and Save tuning file for AutoCal options automatically
appends a sequence number to the filename to make it unique giving users a
history of sequentially numbered files with each saved change made. A
FlashScan device must be connected to save security and/or AutoCal options.
Cummins Fuel Timing Calculator
To open the CFTC, click this icon in the tool bar:
The icon is only enabled when one of the fuel timing tables is displayed for editing.
When you open the CFTC window, the table is pre-populated with the correct
percentages that are required to calculate the currently displayed timing table
values. That allows you to evaluate the existing injection pulse timing. After you
have made any changes to the CFTC table, click the [Apply] button. Applying the
changes will update the underlying fuel timing table so that the injection pulses are
delivered at the timing selected in the CFTC window.
Minimum %
It is sometimes required that the minimum timing does not fall below a certain
percentage. In that case, check the Minimum % check box in the lower left corner
of the calculator window. And set the minimum percentage value.
Setting that value will not change any values displayed in the timing calculator,
instead it will simply force the calculator to compute timing values that are never
less than the percentage value specified when the [Apply] button is clicked.
For example, setting the Minimum % to 5 will force the calculator to treat all cells’
values that are less than 5% as if they were 5% when computing the fuel timing.
How does it work
When fuel is injected, the injection pulse width is some number of micro seconds.
Some tuners would like to set the fuel timing so that the injection pulse will start at
a given crankshaft position relative to top dead center (TDC) of the piston.
The CFTC allows you to specify the percentage of the injection pulse width that
will occur before top dead center (positive values), exactly at top dead center (0)
or after top dead center (negative values).
For example, assuming the injection pulse width for a particular cell is calibrated at
500us (500 micro seconds), then the following percentages in the fuel timing
calculator will result in the injection pulse starting at various crank shaft degrees
for 1000rpm and 2000 rpm: