7.1 Basic / Load Sections 7 ADDITIONAL ITEMS: BEYOND BASIC FUEL AND IGNITION CONTROL
• The TPS reading needs to be below the throttle closed TPS threshold.
• The MAP sensor reading needs to be below the overrun MAP threshold.
• The RPMdot rate needs to be below the fast deceleration threshold (if the engine is slowing that fast, it is
likely that the engine is in neutral and RPM is dropping rapidly, so the MS3Pro will turn on fueling to prevent
the fuel cut from stalling the engine) and below the fast acceleration threshold (which clearly is not an overrun
condition).
7.1.4.2 Tuning engine states Here are some general pointers for tuning the engine states.
Only use the VSS on vehicles capable of engine braking. The VSS should be turned off if your vehicle needs to
idle while in motion. The most common example would be a car with an automatic transmission set up to freewheel
on deceleration. If you have trouble with the engine stalling while the vehicle is moving, but it idles with no problem
while stopped, turn this setting off.
If closed loop idle fails to engage properly, check to be sure the TPS reading does not go above the throttle
closed TPS threshold and that neither the slow deceleration state nor the slow acceleration state are active while
idling. If any of these states are false triggering, increase the threshold values. Also make sure the MAP sensor
reading does not go below the overrun MAP threshold at idle.
If the idle valve closes or opens abruptly when the engine is not idling, you may need to reduce the slow
acceleration or slow deceleration threshold.
If overrun fuel cut fails to engage, check the throttle closed TPS threshold and MAP overrun MAP threshold to
be sure both sensor readings are low enough.
If the engine stalls if you let off the throttle and disengage the clutch at high RPM, check if the overrun fuel cut
engaged. If so, decrease the fast deceleration threshold to lock out the overrun fuel cut in these conditions.
7.1.5 Tacho Output
The tachometer feature provides a pulsed output suitable for connecting to a tachometer (rev counter.) The Tach
Out pin will generate a 0-12V signal that will drive most aftermarket tachometers. The stepper output pins will also
supply a 0-12V square wave. Some older tachometers may need a high voltage adapter if they are designed to
use the pulse from a coil negative terminal or connect inline with the coil power feed wire.
• Tacho output enabled - enables the feature
• Output on - selects the output pin
• Fixed or Variable - Fixed mode allows normal output or half speed. Variable tach output mode allows scaling
the tach output by any percentage from 10% to 1000% of normal tach speed. Note that fixed mode may have
a slight improvement in accuracy.
• Speed - This setting is used in fixed tach mode.
– Normal - an output pulse is generated matching each cylinder event. i.e. 4 cylinder engines have 4
pulses per engine cycle.
– Half speed - output runs at half speed. This can enable a 4-cyl tachometer to be used on an 8-cyl
engine.
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 130
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