MJLJ Frequently Asked Questions
MAP vs. TPS
Q: MAP or TPS: What should I choose?
A: See Choosing between MAP or TPS
Q: How does the MJLJ control rev limiting?
Due to the design of the Ford EDIS module, there is no 'direct' way to control the EDIS module's ignition coil drive. To enable hard rev-limiting the MJLJ offers a 'Rev limit' output which is designed to control an external circuit or device that will electrically disable the ignition coils. This Rev Limit output, like the other programmable outputs, is an 'open collector output', meaning it conducts 'ground' when enabled.
The MJLJ also features a soft rev limit where, 100 RPMs before the configured hard rev limit, the ignition advance goes to zero, significantly reducing the engine's power. Should the engine push past this limit and cross the rev limit threshold, the Rev Limit output on the controller is enabled. The setting of the Rev Limit threshold is accomplished using the Configuration Software.
There are a few experimental circuits for controlling rev limiting- search the community forums for more information. Autosport Labs is currently developiing an outboard module to enable this functionality.
Q: I'm running a boosted A-Series mini. Does the MJLJ support knock control?
A: Knock sensing is a sophisticated problem to solve, as evidenced by companies that offer comprehensive knock sensing solutions like J&S SafeGuard.
There is some good information on the Megasquirt website discussing knock sensing using components sourced from General Motors: .
So the short answer is that the current version of the MJLJ firmware does not support knock control. However, the firmware could be modified to accept an input from a module like the GM unit described above, and then act upon it, typically by retarding the timing in some fashion.
If you read the Megasquirt documentation you will see that the GM module and sensor is tuned a specific way, likely optimized to work well on the GM engines it was designed to fit on.
The question is, does your boosted A-Series knock signature sound like the GM's V8? Is it close, or way off? Is it similar enough to realize *some* benefit? Obviously the same question goes for all engines.
So after that long answer- :) There will be knock control of some sort for either this version of MJLJ or an upcoming version.