7.10 CAN bus / Testmodes 7 ADDITIONAL ITEMS: BEYOND BASIC FUEL AND IGNITION CONTROL
• Pulsewidth Scaling - Setting the pulsewidth scaling reduces the pulse width resolution, but enables four
times the normal maximum pulse width (normally, this is limited to 65 milliseconds). Usually, you would use
this feature on very large, low RPM engines, where the injectors are sized exclusively for operation below
2000 RPM. You also need to enable “PW4X” in Project Properties when using this feature.
• Digital switched 12V In Pulldown - causes the voltage on this pin to default to 0 volts. This ordinarily should
not be changed unless you have modified the MS3Pro internally or connected a highly unusual circuit to this
input.
• Log Trigger Times to Sensors 9-16 - This enables an experimental feature to record engine trigger times
to sensors9-16 to monitor per-cylinder effort. Only for developers.
The SpkAdj values can place limits on a remote device modifying the spark timing over CAN. Currently, the most
likely device to do this is a transmission controller; the MicroSquirt transmission control firmware can retard spark
while shifting to reduce wear and tear on the transmission. Other devices may also adjust timing in the future.
• Maximum SpkAdj Value - Sets a limit on the maximum adjustment a remote device can apply to the ignition
timing. This is a positive number, meaning advance.
• Minimum SpkAdj Value - Sets a limit on the minimum adjustment a remote device can apply to the ignition
timing. This is a negative number, meaning retard.
7.10.20 Long term fuel trim
The MS3Pro can store a long term trim table to flash memory, based on oxygen sensor feedback. Enables the
long-term fuel trim. This is intended to automatically make minor corrections in fueling after the engine is fully
tuned. It requires EGO control to be enabled and operational.
• Enable experimental long term trim - Turns on the ability to store and write long term fuel trim tables.
• Sample interval - How often, in seconds, the code checks the amount of EGO correction being applied.
• Correction softness - Controls how aggressively the trim is applied. Larger numbers mean a softer amount
of correction.
• Write method - Allows you to select writing the trim table to flash based on timed updates or triggered with
an external button.
• Burn button - If using button input, specifies which input triggers writing the long term trim table.
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 278
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