4.4 Other sensors 4 WIRING
Pin Function Connection
A Ground Sensor return
B Sensor output MAP in
C Reference voltage 5V+ VREF Out
MAP sensors will have three pins unless they have some sort of additional sensor (usually a temperature
sensor) in the same package. The reference voltage connects to the MS3Pro’s VREF pin, and the ground pin
to the sensor ground wire. For a voltage based MAP sensor, connect the signal pin to the MS3Pro’s MAP input
wire. An additional MAP sensor may be used to measure barometric pressure on one of the spare analog inputs.
Frequency based MAP sensors such as those used in Ford Mustangs must be wired to a Digital Frequency In wire
instead of the MAP or analog inputs. (You can also use the CMP+ wire for a frequency based MAP sensor, if you
are not using it for cam position.)
4.4.3 Throttle position sensor
The throttle position sensors used on most cars are potentiometer or variable resistance types, which put out a
voltage that increases as the throttle opens. The easiest way to check a TPS is to unplug it and put an ohmmeter
on its pins. Observe the resistance as the throttle opens and closes. Each pair of pins will behave differently:
The resistance between the VREF and ground pins will remain constant. The resistance between the ground
and signal pins will be low with the throttle closed and high with the throttle wide open. The resistance between
the VREF and signal pins will be high with the throttle closed and low with the throttle wide open.
If your sensor behaves like this, it will be pretty straightforward to connect it to the MS3Pro.
If the resistance jumps from infinite (or near infinite) to near zero, you have a switch type throttle position sensor,
or possibly a seriously defective potentiometer type TPS. These do not provide very much information that MS3Pro
needs, as it can tell if you are at idle or full throttle by the MAP sensor information. You can still use MAP based
acceleration enrichment. If the TPS input is not used, this wire should be connected to sensor ground.
4.4.4 Mass air flow sensors
Mass air flow (MAF) sensors provide a measurement of actual airflow through the intake system of an engine. In
its most basic form, the fuel required by the engine (in mass per second) is directly related to the air flowing into the
engine (in mass per second) so the MAF sensor should give a good basis for the fuel equation. By comparison,
Speed Density uses RPM, MAP, MAT and VE to estimate the mass air flow. In practice, like any other sensor input
the MAF has its own quirks and can suffer from reversion effects (particularly on "cammy" engines) where the air
flow gets measured twice.
MAF sensors have at least three wires: Ground, power supply, signal.
• The power supply is typically 12V and should be taken from a fused source from the main relay.
• Signal GND should connect to MS3Pro sensor ground. If the sensor has only one ground, it’s sensor ground.
• If the sensor uses a terminal called Power GND, this should connect to the same point as the MS3Pro power
grounds.
• With a voltage MAF, you may use the MAP signal wire or any of the extra analog input wires.
• With a frequency based MAF, you may use any of the Digital Frequency In inputs, or the CMP+ wire if you
are not using it for cam position.
Here are some of the more commonly seen MAF pinouts.
AMP EFI MS3ProUltimate manual version 1.203, firmware 1.5.0, 5/23/2017 Page 43
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