LETRIPP II XMS4A DIY MANUAL V2.1
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PE
RFECT POWER XMS4A – Engine Management System DIY MANUAL V2.1
17.1.5
SETTING UP THE IDLE
1.
First make all of the relevant targets Zero.
2.
Start the engine and don’t have any extra load on the engine like, headlights, air
conditioner, supercharger, etc.
3.
Enter values into the Idle Minimum % until the engine has reached approximately 1300
RPM. This value is then copied into the Idle Maximum %.
4.
Now the Idle Minimum % must be set by entering lower values into the Idle Minimum %
target.
•
The 2 Wire window will need to be set to approximately 50 RPM.
•
Set the Idle target map to be lower than your ideal idle RPM.
•
A value in the 2 Wire Adj. Step is needed now to allow the XMS4A to reduce the Idle
PWM signal. Start off with small numbers until you get the feel for it. Once the RPM is
at the lowest you would ever like it to go, this value is now your Idle Minimum %.
5.
The Idle target RPM map can now be set to your desired idle targets.
6.
Make sure that the idle is stable and that the RPM is smooth before proceeding.
Now the Idle motor will need to react fast when extra load is applied to the engine, the Idle
Kick Open % and the Idle Kick Window will be setup for this. Use these numbers as a
guideline: Idle Kick Open % 5. Idle Kick Window 50. Each idle motor reacts differently so you
will need to experiment with the settings yourself. To test how your settings will react to load
conditions you can turn on the air conditioner or the headlights.
In the graph above we can see that the RPM in Red, drops below our target RPM and falls
below the Idle Kick Window. The XMS4A detects the RPM drop and invokes the “Kick” as seen
in the green graph. The “kick” open will gradually return to the same PWM before the RPM
drop was detected.
To aid the engine when extra load is applied at idle, the XMS4A can make the fuel mixture
richer. The Kick Open Enrich is used to add more fuel once the “Kick” is detected. Use a value
of 25 for starters and work from there.
18.
DWELL TIME
This section covers the dwell time, which is important to have proper spark.
18.1
WHAT IS DWELL?
Dwell is the length of time that the coil is charged. The XMS4A is able to control the dwell at
24 different RPM sites. This means you can have longer charge times at idle and short charge
times at high RPM.
18.2
CAN IT DAMAGE YOUR COIL?
Yes. Setting the dwell time too long (20ms) will cause the coil to become saturated. A
saturated coil will overheat and will burn out over time. Setting the dwell too short (1ms) will
not damage the coil. A very short dwell time will cause a weak spark and the engine may
misfire. To check if the coil has the right dwell time you will need an oscilloscope to measure
the current.