7.6 Boost / VVT 7 ADDITIONAL ITEMS: BEYOND BASIC FUEL AND IGNITION CONTROL
7.5.3.6 X-Tau tuning tips You should start with low X and low Tau, such as the default values. You should then
see if the X-Tau helps. Start by adjusting the X factor. If that doesn’t help, try increasing the Tau time table entries
in the areas where you are having troubles with lean spots (engine coughs on accel).
The Tau time table is deliberately conservative, so in most cases it will require increasing, by perhaps 50% to
100%.
You may need to try adjusting the lag filter values for the MAP sensor for less filtering. The X-Tau mode needs
to see the rapid rate-of-change of MAP and the lag filters can reduce this if set too low. Generally you do not want
to set it to less than 50%, and may need to set it to 70% to 80%.
As you dial-in the X-Tau parameters, the engine will likely become overly rich due to both normal and X-Tau
enrichments being applied. You can try reducing the existing TPSdot or MAPdot based accel/decel enrichments,
which do NOT go away when you specify the X-tau option and increasing the X-tau variables. (Note that you may
have to increase the cold accel multiplier as you do this.)
7.6 Boost / VVT
The MS3Pro has multiple boost control strategies, and can control up to four channels of continuously variable
valve timing.
7.6.1 Boost control basics
7.6.1.1 Boost control strategies The MS3 Firmware has four primary algorithms for controlling boost:
• Open-Loop Single Solenoid - Solenoid duty comes from an 8x8 duty table of TPS vs RPM.
• Closed-Loop Single Solenoid - A Proportional-Integral-Derivative (PID) loop controls solenoid duty to match
the actual boost to the boost target. Closed loop control starts by using a bias table to look up what duty
cycle to start with for a particular RPM and target boost, and then uses the PID loop to apply a correction
factor to hit your target boost. An 8x8 target table of TPS vs RPM or a 6-point boost vs vehicle speed curve
is used to figure out the boost target.
• Open-Loop Dome Control - The MS3Pro uses a pressure sensor in the wastegate dome and a closed loop
algorithm to specify a target pressure in the wastegate dome. The ECU does not attempt to target a particular
MAP sensor reading. This uses a reservoir of CO
2
or compressed air, and two solenoids, one to let CO
2
into
the dome and the other to vent it to the atmosphere.
• Closed-Loop Dome Control - This also uses a wastegate dome pressure sensor, CO
2
, and two solenoids.
However, this algorithm targets a MAP sensor reading by using a table showing what dome pressure should
produce a target boost pressure at what RPM. The ECU then uses a PID loop to adjust the target dome
pressure up or down if this does not hit the target boost table, while using a separate closed loop algorithm
to make sure the dome pressure reaches its target.
There are also several modifiers that allow you to change the boost level based on timing, gear, measured wheel
speed, or other factors, on top of the primary boost control algorithm.
7.6.1.2 Boost control hardware You can wire a boost control solenoid to any unused high current or injector
output, as shown below. Boost solenoids normally do not have a polarity; the two wires can be hooked up in either
order.
pre
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 200
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