7.1 Basic / Load Sections 7 ADDITIONAL ITEMS: BEYOND BASIC FUEL AND IGNITION CONTROL
7.1.2.2 Coolant temp limiter The curve defines an alternate hard rev limit based on coolant temperature. You
can use this to limit RPM with the engine cold or to create a shut-off if the engine is overheating, or both.
• Rev limiter coolant based -
– Normal - The above settings are used independent of coolant.
– CLT Based - the curve is used to select a rev limit based on coolant temperature, so that lower limits
can be applied to a cold engine. When selected, the graph on the right hand side of the screen defines
the rev limit.
• Rev limit TPS bypass% - above this TPS% the coolant curve is ignored, and it uses the standard rev limiter.
This should be set to a high percentage number, so that only in an emergency when you really need full
throttle on a cold engine can you override the cold limit.
7.1.2.3 Spark retard The MS3Pro has several different spark retard strategies. You specify the timing retard in
an absolute angle which the MS3Pro will use as your timing; the timing specified here is not an amount of timing
to pull but the total amount of timing to use. The spark retard begins at the soft rev limit - the hard limit minus the
soft zone number.
• Mode - Select how
– Off - no spark retard rev-limiting is used.
– Progressive Retard - the timing is progressively retarded between the “retard above” threshold and hard
rev limit. The retard starts just above the "retard above" rpm and reaches the maximum set retard by
the "fuel cut" rpm.
– Fixed angle - when the "retard above" rpm is reached the spark timing is immediately changed to the
rev limiter timing.
• Maximum retard - the maximum amount of timing retard that will be applied
• Retard to - the fixed spark angle that will be used.
7.1.2.4 Spark cut Where MS3Pro is directly controlling spark, spark cut can be used as a rev limiter method.
This cannot be used with EDIS and will not work as expected with TFI, GMDIS or C3I, as these systems have
some level of independent spark control. Be aware that spark cut can be harsh and should not be used with
catalytic convertors due to the damage it causes. Frequently, there will be some level of "popping and banging"
and exhaust system damage may occur. Use at your own risk!
The spark cut algorithm cuts sparks on a "round-robin" basis to prevent individual cylinders loading up with
unburned fuel. The cut begins at the soft limit value and the percent of sparks cut increases up to the hard limit,
where the MS3Pro shuts off the spark entirely
7.1.2.5 Fuel cut This gives the option of an abrupt, total fuel cut, or cutting fuel to more and more cylinders
until a total fuel cut at the hard limit.
• Enable Fuel Cut Limiting - Turns on fuel cut rev limiter.
• Progressive Fuel Cut - If this is turned off, the fuel cut applies abruptly when you reach the hard limit. If this
setting is on, the MS3Pro will shut off fuel to one cylinder at the soft rev limit and ramp this up to cutting all
cylinders at the hard limit. This does not rotate between cylinders like the spark cut - once the cylinder is off,
it remains off until the RPM drops enough to turn it on. Note that this cannot be used with throttle body
injection or staged injection. This only works with one injector per cylinder.
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 127
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