7.6 Boost / VVT 7 ADDITIONAL ITEMS: BEYOND BASIC FUEL AND IGNITION CONTROL
2. Set Proportional gain to 100% and slowly lower - While tuning Proportional gain, higher numbers mean
slower boost climb and lower final boost. For safety, start with a very high gain (100% should be sufficient).
Find the RPM that typically spools quickly, and fully and quickly depress the accelerator. Note how much
boost is reached. If boost overshoots the target dramatically, increase the Proportional gain. Otherwise,
reduce the Proportional gain and try again. Do this until boost reaches the target with a small amount of
overshoot.
3. Tune the Integral Gain - The next step after the target is reached consistently is to tune the Integral gain.
Starting from the RPM used to tune the Proportional gain, fully depress the accelerator and watch the boost
as the engine climbs through the RPM range. As the engine accelerates through the rev range, the boost
will probably creep away from the target. Keep increasing the Integral gain until the controller adequately
maintains the target with minimal oscillation. It may be necessary to increase the Proportional gain a bit after
tuning the Integral gain since the two gains tend to counteract each other.
4. Tune the Derivative Gain - Increase the Derivative gain until the overshoot is minimized. Care must be
taken when increasing the Derivative gain as too much Derivative gain can over-dampen the effects of the
Proportional and Integral gains.
7.6.2.3 Overboost Protection Overboost protection works similarly to a rev limiter, except that it can stop
engine operation when boost exceeds a user-set limit. In addition, use of the overboost protection feature is re-
quired when using the closed-loop boost control algorithm. The following settings affect the operation of overboost
protection:
• Overboost Protection - Activates overboost protection and lets you specify what action to take when boost
exceeds the maximum boost number.
– None - Disables overboost protection.
– Fuel Cut - Stops the engine by cutting fuel.
– Spark Cut - Stops the engine by cutting spark.
– Both - Stops the engine using both fuel and spark cut.
• Maximum Boost - The maximum boost (in kPa) at which the engine should be operated.
• Hysteresis - The amount boost must drop by (in kPa) after hitting the maximum boost before fuel or spark
are restored.
• Boost Tolerance - Turning this on in closed loop mode creates an alternate maximum boost value equal to
your boost target plus the tolerance value set below. The MS3Pro will use either the maximum boost level or
the number generated by the boost tolerance at your RPM and throttle, whichever number is lower. Allows
the overboost protection to track with closed loop boost control for engines that can run more boost at some
points of the RPM range than others.
• Overboost switching - Allows you to use an input to raise or lower the point at which overboost protection
engages. For example, you might want one setting for pump gas and another for race gas, and can use a
switch to let the MS3Pro know which you are running.
• Alt Maximum Boost - The boost level to allow when the overboost switch is active.
Setting this ups very similar to setting up a rev-limiter. Choose from Fuel Cut or Spark cut or Both. Do not use
spark cut mode if the engine still has a catalytic converter. Spark cut can cause backfires that melt or break the
catalyst.
The maximum boost should be set up higher than the maximum target boost will be in the closed-loop boost
target table. Hysteresis should be set so that MAP jitter does not cause it to alternate rapidly between on and off.
Remember, overboost protection is not telling the MS3Pro “I would prefer my boost level stays below this setting;”
it is more like, “Shut down my engine at once if the boost gets this high!” And the MS3Pro will react with that
same level of urgency.
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 204
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