LETRIPP II XMS4A DIY MANUAL V2.1 www.perfectpower.com 5
PERFECT POWER XMS4A – Engine Management System DIY MANUAL V2.1
6. FEATURE EXPLANATION
6.1 LAUNCH CONTROL
The Launch Control is for turbo cars where “spooling up” of the turbo is required on the start
line. It is an extra switch input. The Launch Control is affected and works in the following way:
Proportional retard above a settable launch RPM limit. When the clutch is depressed (pushing
a switch) the ignition is retarded when a specified RPM is exceeded and advanced back to
normal when the clutch is released.
The Launch Control feature can also be used for “Flat-foot-shifting” in non-turbocharged
engines. This restricts the RPM to a specified level while the clutch is pressed and the
accelerator is pressed down.
6.2 EXTERNAL SUPPLY TO SENSORS
A separate +5 Volt output (pin 9 of 22) is available to power manifold pressure and TPS
sensors.
6.3 MAPS A / B
The XMS4A has two complete maps for all tuning data. Maps can be switched while driving.
The two maps can hold different tuning for weather, fuel grade or performance requirements.
The maps can be switched from a manual input, or automatically via the SETPOINT procedure
in the LetRipp Software.
6.4 CALIBRATION
All inputs can be calibrated to suit your existing sensors of your engine. Calibration is
performed for two reasons:
A) So that the XMS4A interprets the sensor readings correctly.
B) So that the Tuner (you) can read the data in engineering units (Bar/PSI,
Fahrenheit/Degree C, other).
6.5 FUEL INJECTION MAP
This map controls the fuel injection. The amount of fuel injected can be mapped on 384 sites
(main map) and the output of the three possible side maps can modify the main map value.
The entry is in counts, 100 counts = 1.00mS.
6.6 IGNITION MAP
This map controls the ignition. The ignition angle in degrees is from the 384 main map sites
and is further modified in the possible three side tables of 24 map sites each.
6.7 COMPENSATION MAP
This map contains various items:
• Acceleration enrichment
• Dwell time specification
• Priming
• Idle target control
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