MJLJ V3 Operation Guide

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First time use

Installing Configuration Software

Download the version of the Configuration software that matches your controller firmware. It's likely you have a very recent firmware image, so start by downloading the latest version of the Configuration software.

Setting the Serial Port

Find and run the Configuration software by finding the icon under the Start Menu program group. Once the program is running, you can set the serial port the MJLJ is connected to by clicking Tools/Configurator Options.

Mjlj controller options screenshot.png

If you don't know which COM port you have the MJLJ connected to, you can discover this under Windows Device Manager: Find the 'My Computer' icon, right-click and select Properties. From this window you will be able to access Device Manager.

Expand the 'Ports (COM & LPT)' to see the list of installed COM ports.

Windows device manager screenshot showing com ports.png

Once you're certain which COM port you're using for the MJLJ, select this value in the options dialog.

Configuring MAP or TPS

In the Controller Options dialog, select the Load type you have for your MJLJ- Throttle Position sensor(TPS) or Manifold Absolute Pressure (MAP).

Configuring Normally Aspirated or Forced Induction

Check the 'Normally Aspirated' box if that matches your engine type. This setting will scale the load axis for the runtime and logging views to 103KPa maximum.

Otherwise, leave the box clear if your engine is turbocharged or supercharged. This will set the maximum scale to 255 KPa (approximately 21 PSI of boost)

Connecting to the MJLJ

Verifying Connectivity

After setting the COM port, connect the serial cable to the MJLJ and apply power. If you already have the MJLJ wired into your engine's wiring harness, turn the ignition key to 'on'. If you are testing the MJLJ on the bench, you can simply power the unit with a 9V battery or a suitable 9-15V power supply.

The first way to verify connectivity is to observe runtime data on the screen. On a running engine you'll see the real-time RPM, load and ignition advance values on the gauges at the bottom of the window.

If you're testing on the bench or on a non-running engine, you will still be able to observe some runtime activity by simulating load changing on the engine. For TPS- move the accelerator pedal; MAP- you can manually apply pressure or vacuum.

Mjlj main screen connected.png
Successfully connected to the Megajolt Lite Jr.

Common connection problems

If the Configuration Software cannot connect to the MJLJ, you will see one of the following messages in the status bar:

Timeout reading runtime data

The Configuration Software did not get a response from the MJLJ on the serial port you specified.

  • Does the MJLJ have power, and connected to the computer with a standard serial cable or compatible USB-Serial adapter?

Could not open port

The Configuration Software could not access the serial port you specified.


  • The port is invalid: Check Device Manager for the proper serial port.
  • Serial port in use: If another program is using the same serial port your computer will block the Configuration software from accessing the serial port. Check that you don't have any other software which may open and use the serial port you're trying to use, such as PDA sync software.

At a glance: Main Screen

The following will orient you towards the main components of the configuration software. Operation guide config software runtime screen reference.png

Runtime Gauges

The runtime gauges show the current engine parameters.

Ignition Advance

This is the actual ignition advance calculated and commanded to the EDIS module. This value should correspond to direct measurement of ignition advance, e.g. observation with a timing light.


This shows the Engine's RPM. The yellow and red regions reflect the current rev limiter setting. The yellow region marks the soft-rev limit region; the red marks when the Hard Rev Limit output is enabled.


The load gauge shows either KPa or TPS %, depending on your Controller's configuration and Configuration software setting. For MAP sensor based MJLJ's the scale can be further adjusted to show 0-103 KPa for normally aspirated engines. With forced induction applications the gauge can be set to show the full 0-255KPa range supported by the on-board MAP sensor.

Working with the Ignition Configuration

Retrieving the Ignition Configuration

To read the controller's current configuration, click the toolbar icon Mjlj read config toolbar.jpg. The current ignition configuration will be read from the MJLJ and displayed in the grid.

Ignition Map

The ignition map organized as a 10 x 10 grid of ignition advance values, with Load/RPM bins defining the steps between grid values.

  • Load Axis: The Load axis is is represented vertically, from low engine load at the top to high engine load at the bottom.
  • RPM Axis: The RPM axis is represented horizontally, from low RPM on the left to high RPM on the right.
  • Bins: The steps between engine load and RPM points are defined as 'Bins'- these are the values shown along the borders of the Ignition Map grid.
  • Ignition Advance: Each cell in the grid represents an ignition advance value, in actual degrees before top dead center (BTDC).

Editing Ignition Map

Adjusting ignition advance

  • Changing single value

To change an ignition advance value, click in the cell you wish to change- the cell will change to editing mode and allow you to change the value.
Mjlj operation guide edit single.png

  • Changing multiple cells

To change multiple cells at once, select a region of cells much like you would with a spreadsheet program. You can select contiguous regions by clicking and dragging, or select individual cells cells by holding down the control key while clicking.

Once you've selected the cells you wish to change, right click the selected group and select 'Set Value'. A dialog will pop up and prompt for the new value.
Mjlj operation guide edit multiple values.png

  • Ignition Advance range: Allowable ignition advance range is 0 to 59 degrees BTDC.

Adjusting Load / RPM Bins

To change the Load or RPM bins perform one of the following:

  • Click the 'Edit' menu and select'Edit RPM and Load bins'
  • Ctrl-B in the main window
  • Right click on the Load or RPM bins in the grid and select 'Edit RPM and Load Bins'

The Edit Ignition Bin values dialog will appear. Here, you can edit the bin values for the Load and RPM axis. Mjlj operation guide edit bin values.png

Edit the values and click 'OK' to confirm your changes.

Controller Options

To access the various MJLJ controller options, click the 'Options' tab below the ignition grid.

Mjlj operation guide controller options.png

Engine Configuration

Select the number of cylinders for your engine (4,6 or 8 cylinders), matching the EDIS module you are using.

User Configurable Outputs

The Megajolt Lite Jr. offers four identical configurable outputs, each with customizable activation.

Output Type
  • Load: Select this type to activate on a Load threshold.
  • RPM: Select this type to activate on an RPM threshold.
Output Mode
  • Normal: The output will be enabled at or above the set activation point and disabled below set activation point.
  • Invert: The output will be disabled at or above the set activation point and enabled below the activation point.
Activation Point

The Activation point sets the RPM or Load threshold for triggering the output.

Hysteresis on outputs

  • RPM configured outputs: Hysteresis is set at 100RPMs.
  • Load configured outputs: Hysteresis is set at 1 load unit (MAP KPa or TPS %).

For wiring instructions on the User Configurable Outputs, see the Installation Guide.

Shift Light

The Shift Light output is activated when engine RPM reaches the configured threshold. Typically this output would be used to illuminate a dashboard-mounted light. For shift light wiring instructions, see the Installation Guide.

Rev Limit

The Rev Limit output is an RPM switch with special behavior.

  • At the specified RPM threshold, the Rev Limit output is activated and can be used to trigger an external Rev Limiter module, such as the Autosport Labs Hard Rev Limiter
  • 100 RPMs before threshold the ignition advance goes to zero BTDC to act as a 'soft' rev limiter by significantly reducing engine power. Together with an external hard rev limit module this provides an effective rev-limit solution, naturally excluding mechanical over-rev situations.

For instructions on wiring an external rev limit module, see the Installation Guide.

Writing the Ignition Configuration

After editing the ignition map or controller options, you may write the changes to the controller. To do this, click the Write Ignition Configuration toolbar icon Mjlj write config toolbar.png to write your changes to the controller.

These changes are made to the Controller's RAM memory, which is used for the actual runtime operation. Therefore, the changes you make may reflect in the engine's operation. For example, if you are tuning the idle region and you alter ignition advance values in map where the engine is idling, you should observe a change in the engine's behavior once you write the configuration to the controller.

Important Note: Writing the ignition configuration only updates the Controller's RAM. 
If changes are not persisted to the controller's Flash memory, the changes will be lost 
if the controller loses power (e.g. ignition key turned to 'off')

This behavior is by design. Persisting the data to flash requires a significant amount of time
and momentarily pauses the controller's operation while the flash memory is written.

Commit to Flash

To make the changes permanent in the Controller's flash memory, Click the 'Commit configuration to Flash' toolbar icon Mjlj flash config toolbar.png. The controller will write the configuration to flash memory, and changes will be preserved after the controller loses power.

Additional Options

Load Axis Calibration

If you have a TPS-optioned MJLJ, you can calibrate the Load axis to reflect actual throttle opening percentage.

With the MJLJ powered up, click the 'Tools' menu and select 'Load Axis Calibration'. You will see the Load Axis Calibration dialog.

Mjlj operation guide load axis calibration dialog.png

Guided TPS calibration

To calibrate your Throttle Position Sensor, click the 'Calibrate TPS' button on the screen and follow the on-screen prompts.

This guided process reads the closed and open throttle position, generates a new load axis table and Flashes the new table to the controller. Once this is performed, it should not require additional changes unless the throttle linkage or sensor is adjusted or modified.

Advanced Uses

Aside from calibrating a TPS-optioned MJLJ, you can also directly edit the load-axis calibration data. For example, if you're using a non-standard external MAP sensor you can load the sensor's voltage curve using this dialog.

Load / Save calibration

You can load and save the Load axis calibration data using the 'Load Calibration' / 'Save Calibration' buttons. The file is in plain text format of 256 values, with the file's line number representing the ADC voltage (line 0 = 0v; line 255=5.0v; linear scale).

The value on each line maps the ADC voltage to the desired load in KPa or TPS %.

Edit Values

The Load calibration data can be retrieved, inspected and modified directly using 'Read Calibration' / 'Write Calibration' buttons under the 'Edit Values' section.

Dual Switchable Ignition Configurations

The Megajolt Lite Jr. supports on-the-fly switching between two Ignition Configurations. Each independent configuration includes the entire ignition map and all controller options (Engine type, User-defined outputs, Rev limit and Shift light settings).

Enabling Switchable Ignition Configurations

To use this feature requires it to be enabled in the Controller's firmware. Open the Global Configuration Options dialog by clicking the 'Options' Menu and then selecting 'Global Controller Options'.

Mjlj operation guide global controller options.png

The Software will attempt to read the Global Controller Options when you open the dialog, so ensure the Controller is powered on and connected to your computer.

Click the check box 'Enable Dual Ignition Config', and then click 'Write Options'. This will immediately flash the Global Configuration data to the controller's flash memory.

Enable hardware switch

Switching between ignition configurations requires wiring the option switch to the Controller. Refer to the Installation Guide for more information.

Configuration software behavior

Once enabled in the controller, the software will alert you when the controller switches to a different ignition configuration. You can define how the software reacts to the switch:

  • No Action: The software only alerts you of the change.
  • Prompt to read configuration: The software prompts you to read the Ignition Configuration the controller was just switched to.
  • Auto-Read configuration: The software automatically reads the Ignition Configuration the controller was just switched to, discarding any in-progress changes made in the software.

Important Usage Notes

The switchable Ignition Configurations can be thought of two controllers in one; or, one controller with two different personalities.

This means you must manage the two Ignition configurations independently by separately reading, writing and flashing the Ignition Configuration as appropriate.

Tuning your Ignition Controller

Charting / Runtime view

You can monitor the runtime operation of the engine, plotted over time by selecting the Charting/Runtime view.

Mjlj operation guide charting runtime view.png

Tuning Perspective

The configuration software offers a 3D interactive editor which makes it easy to tune the ignition map and Load / RPM bins while the engine is running.

Mjlj operation guide tuning view.png

In this view you will see a contour plot of the ignition map, with the ignition advance as the elevation of the surface. 'Hot' colors indicate more advance, and 'cool' colors indicate less.

You will see two bouncing balls: The red ball indicates the current run-time cell the controller is using for the ignition advance; this will move around as the engine RPM and load changes.

The yellow ball indicates your current editing point.

Editing the Ignition Map

  • Navigation: Use the arrow keys to move the editing point around the Ignition Map.
  • Increase/Decrease advance: To increase advance at the editing point, hold down the ctrl-key and press the up arrow key. Conversely, to decrease the ignition advance, hold down the ctrl-key and press the down arrow.
  • Modify Load/RPM bins: You can increase/decrease the selected RPM bin by pressing Alt-left arrow / Alt-right arrow. Correspondingly, the selected Load bin can be modified by pressing Alt-up arrow / Alt-down arrow.

Hot Keys

  • Lock editing with runtime: Pressing 'L' on the keyboard toggles locking the editing point (yellow ball) with the runtime point(red ball), making it easier to edit the map in the region where the engine is running.
  • Enable real-time config update: Pressing 'U' on the keyboard toggles real-time updating of the edited ignition point. The values are stored in the Controller's RAM, but not persisted to flash.

Data logging

The MJLJ Configuration software provides the ability to log runtime data to a file for later analysis.

Starting a Data logging Session

To start a Data Logging session, click the menu 'File' and select 'Start Datalog'. You will be prompted to supply the filename of the Data logging file.

Quick Data Logging

You can start a quick Data Logging session by clicking the Menu 'File' and selecting 'Quick Datalog' - or press F5 in the main window.

The file will be automatically created in the last selected directory with the automatically generated file name "MJLJ_Log_<DateTime>.csv" For example, "2007-11-26_19.57.02.csv"

If you select 'Quick Datalog' while a Data Logging session is active, the current file will be closed and a new file started.

Mark Datalog

To mark a noteworthy event while a Data Logging session is active, click the Menu 'File' and select 'Mark Datalog' - or press Space Bar

Stop Logging

To stop logging, select the menu item 'File' and select 'Stop Datalog' - or press ESC in the main window.

Logfile Format

The contents of the log file is stored in a plain-text CSV format. You can read this file with a standard text editor or a spreadsheet program like OpenOffice Calc or Microsoft Excel.

  • Timestamp: The time of the log file entry
  • RPM: Engine RPM
  • Load: Engine Load, in KPa or TPS %
  • Advance: Ignition Advance in degrees BTDC
  • RPM_Accel: RPM Acceleration, in RPM/sec
  • Load_Accel: Load Acceleration, in KPa/sec or TPS/sec
  • Mark_interval: Indicates a marked portion of the log data. 1 = Marked.

Advanced Topics

Configuring PIP noise filtering