AEM 30-6905 Universal Programmable EMS-4 - Manual (Page 208)

Page 208 of 279 EMS-4 Install and Tuning Guide_Rev 1.6
The Alt Function is another unique feature of the EMS. It‟s most often used in conjunction with
the 2 step rev limiter to create a turbocharger anti-lag function. A turbocharged drag race
vehicle can use this function to build boost on the starting line. The Alt function when activated
can retard the ignition timing and add fuel effectively turning the turbine housing into a fuel
afterburner. This adds tremendous energy to the turbocharger and increases turbine speed,
building boost. In this example, we are simply using the function to trim fuel and spark and
activate a switched ground output at the same time.
Alt Function Input – Channel that activates the alternative trims.
Alt Ignition Fixed - Enables the fixed ignition state where the user can force the ignition timing
to a fixed value regardless of any other influence.
Alt Spark Fixed - Defines the fixed ignition timing value in degrees when option Alt Ignition
Fixed enabled.
Alt Spark Trim - Amount of ignition spark to be trimmed (+/-) when the alternate trims are
active.
Alt Fuel Trim - Percentage of fuel to be added when in the alternate switched condition.
Alt Off Above RPM - When above this rpm, the alternate trims and functions will deactivate.
Alt On Above RPM - When above this rpm, but below the Alt Off Above RPM, the alternate
trims and functions will activate.
Alt Off Below TPS – When below this value, the alternate trims and functions will deactivate.
Alt On Above TPS – When above this value, the alternate trims and functions will activate.
Alt OK Below VSS – The maximum vehicle speed threshold for the Alt Function.
Alt Overboost - When above this value, the alternate trims and functions will deactivate.
Alt On Above Load - When above this load value, but below the Alt Overboost value, the
alternate trims and functions will activate.
Alt Function Output - If the Alt function is activated, this output channel will be activated also.
Can be used to drive an LED, injector or whatever.
In our example, if above 50% throttle and 500 RPM AND the GPIO5
analog voltage falls below 3.51 volts, Switch 7 will turn on activating
the Alt Function. The alt function will retard the ignition timing by
10.2 degrees and add 10% to the current fuel pulse. The ALT function
will also activate low side switch GPIO1 which can be used to drive a
warning lamp relay.