AEM 30-6905 Universal Programmable EMS-4 - Manual (Page 119)

Page 119 of 279 EMS-4 Install and Tuning Guide_Rev 1.6
The MAP sensor provides manifold pressure information to the ECU for calibration based on
MAP vs. RPM. The MAP information is used in both the fuel and ignition Y-axis of their
respective maps. On racing engines that use individual runner manifolds, a TPS based fuel
map can be used while the ignition can be MAP based. This is desirable because the ignition
should always be load based to provide knock free operation.
A MAP sensor reads in absolute pressure, just like the name implies. The amount of pressure
indicated by the sensor depends on the amount of voltage feedback delivered to the ECU. As
the throttle is opened and closed, or boost is built up in the manifold, the sensor reacts to the
changing pressure and outputs a voltage signal to the ECU based on the given pressure.
The MAP sensor has three leads: 5V+ into the MAP sensor, a return to the ECU based upon
the resistance of the MAP sensor, and a ground. A MAP sensor MUST have a hose routed to it
from the inlet manifold in order to read manifold pressure and it MUST receive a constant
pressure signal to it at all times. If the pressure signal fluctuates, the calibration will be
adversely affected because the fuel and ignition values will cycle with the MAP signal.
To avoid varying MAP signals, the pressure line must be connected to the intake plenum. In the
case of individual runner manifolds, TPS-based mapping is best.
If a MAP sensor is used for boost compensation or load sensitive ignition timing, an accumulator
must be used. An accumulator is a common closed container that has a hose from each runner
routed to it. An accumulator dampens the pulsing commonly found in this type of manifold set
up, which will aid in the delivery of a steady MAP signal (A fuel pressure regulator can have its
pressure source routed to an accumulator for the same reasons).
The AEM PEMS has a variety of MAP sensor ranges to suit everything from naturally aspirated
engines, to forced induction engines up to whatever boost can be generated by the turbo or
supercharger(s).
Air Temperature Sensor
Manifold Air Temp Sensors (MAT) and Inlet Air Temp Sensors (IAT) are variable resistance
thermistors that send a return voltage signal back to the ECU based on the inlet air temp either
in the inlet manifold or in the inlet duct to the throttle body (The ECU outputs a +5V power to the
sensor and the return voltage is based on the resistance of the sensor). These sensors can
also be used as auxiliary temp sensors for any air temp measurement, such as intercooler inlet
and outlet temps.
The AEM EMS is compatible with virtually all MAT & IAT sensors. Based on the inlet air temp
readings provided by an MAT or IAT, an ECU can add or subtract fuel or ignition timing
depending on the given conditions. For example, a typical use for an MAT sensor is to change
the ignition timing and fueling of an engine based on inlet air temp. This is particularly useful on
forced induction engines where inlet air temps can increase dramatically.