5.5 Sensor calibration 5 SETTING UP A BASIC CONFIGURATION
• Power Between Steps - Determines what to do when the valve is not moving.
– Moving only: Turns off current to the idle valve. This can reduce current consumption and make the
valve run cooler, but can result in unreliable operation for some valves. Usually this should only be used
for valves that do not freewheel if you try spinning the pintle by hand.
– Hold current: Applies a 50% current to keep the valve in place. Something of an intermediate position
between the other two options. Should be used with any valve that spins freely if you attempt to turn it
by hand. If you run into problems with the stepper valve drifting, switch to “always on” instead.
– Always on: Applies full power to the last coil to move to prevent the valve from turning. This can make
the valve and the drive circuit run hotter and makes the MS3Pro draw more current, but locks the valve
in position.
The amount to move the valve is specified in additional menus. Also, see section 6.1.1.3, Idle Valve Testing, for
troubleshooting common problems with a stepper IAC valve.
5.4.3 PWM idle valve settings
• Crank-to-Run Taper Time - This is the amount of time the IAC valve uses to transition after starting from its
crank position to its running position.
• Valve Mode - Normal mode is off at 0% duty cycle, inverted mode is off at 100% duty cycle. As the name im-
plies, most valves use normal mode. If you’ve found you accidentally wired up a 3 wire IAC valve backwards,
just flip this setting.
• Output Port - Allows you to pick which output wires are used. In 3 wire mode, this is for the coil that opens
the valve.
• 3 wire mode - Used with 3 wire rotary IAC valves, common in Denso and Bosch applications. Set to Off for
a 2 wire valve. For a 3 wire valve, this specifies the connection used for the coil that closes the valves.
• Valve Frequency Selection - Select a frequency from the list. Different valves operate best on different
frequencies.
The PWM idle control uses two additional menus, PWM Idle Cranking Duty and Idle PWM Duty Table. These
specify the IAC position in cranking and running as a function of temperature. A third menu, PWM Idle Voltage
Compensation, lets you specify an amount of duty cycle to be added to or subtracted from the duty cycle as a
function of battery voltage.
5.5 Sensor calibration
The MS3Pro uses internal calibration tables to convert the resistance/voltage from the input sensors into a real
world number. It is necessary to setup this calibration so the inputs read correctly. The built-in calibrations for
coolant temperature (CLT) and air temperature (MAT) are for GM sensors, so if you have GM sensors you are
safe to leave these alone. All installs should set the calibration for the AFR (air fuel ratio) table that is used for the
oxygen sensor (lambda sensor) whether narrowband or wideband. Here’s how to change the sensor calibrations.
1. Unlock the calibrations (This lock/unlock is to ensure the calibration isn’t changed by accident.)
2. Open the Set Thermistor Tables dialogue, then set the CLT calibration (if needed) Pick the sensor type.
The bias resistor value is hardwired at 2490. For a custom sensor, enter three measured temperature and
resistance pairs. (Don’t guess, measure.) For greatest accuracy the bias resistor should be close to the
sensor resistance at a "warm" temperature. Write to controller.
3. Set the MAT calibration in the same way (if needed.) The bias resistor is 2490 ohms. Write to controller.
Close the dialogue.
4. Calibrate the AFR table. Either pick a preset or look up the voltage/AFR pairs from your controller manual.
Write to controller. Note! You should also set your Project Properties for narrowband/wideband and configure
the settings on the “EGO control” page.
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 99
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