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Ignition Control with the MegaSquirt-II™/MicroSquirt® EFI Controller

To provide improved engine performance, better fuel economy, and reduced exhaust emissions, MegaSquirt-II™ or MicroSquirt controllers can control spark advance (timing), and this advance is fully programmable by the user. These controllers have the ability to control a variety of ignitions which have 1 coil and a mechanical distributor to distribute spark (such as the GM 7-pin HEI module), as well as the Ford EDIS and GM DIS ignition.

Some ignition modules supported include:

In addition, the MegaSquirt-II™ (and MicroSquirt®, applies to all mentions of MS-II in this document) EFI controller has support for a number of distributor pickups, such as Hall sensor, VR sensor, points, and optical sensor. These can be matched to some of the above options.

The key to MegaSquirt-II ignition control for modules not listed above is that the MegaSquirt-II™ EFI controller can trigger on the rising or falling edges of the input signal, and can program 'spark' on the rising or falling edge of the output signal.

By adjusting the dwell control parameters, a very wide range of duty cycle output signals can be sent (as well as straight dwell control for 'dumb' module like the 8-pin HEI).

The ability to change the 'input capture' gives you the option of configuring the trigger as the leading edge of the square wave, or the trailing edge. An example of a trailing edge firing is a mechanical points (Kettering) system, where the points cause the coil to fire when they open (pulling the +12 volt voltage 'signal' on the coil to ground). Some ignition systems may require triggering on the leading edge, however.

Most modern electronic ignitions use one of three types of sensors in the distributor (or crank sensor). They use either a:

  1. variable reluctor sensor,
  2. a hall sensor, or
  3. an optical sensor.

All this means that most ignitions system modules could potentially be supported by the MegaSquirt-II™ EFI controller , if the user did the homework to find out which combination of settings applied to their ignition module.

Other than wasted spark systems with dedicated modules (like the Ford EDIS system), the MegaSquirt-II™ EFI controller does not support multiple coil configurations for more than 2-cylinders at this point. However, the upcoming MS-II Sequencer™ is intended to provide full Coil-On-Plug (COP) support (as well as sequential fuel injection) for up to 8 cylinders.

The MegaSquirt-II™ EFI controller can control the ignition advance timing based on rpm, load (engine MAP), and coolant temperature. This means you have the ability to program full 'mechanical' and 'vacuum' advance, and the user can program in any amount of boost retard simply by reducing the advance table entries over 100 kPa. Later version of the code also have provisions for ignition advance retard based on intake air temperature.

The MegaSquirt-II™ EFI controller installation, including the wiring diagrams, are on the installation page and specific ignition module pages linked off that page. However, in general:

Older engines might use mechanical contact points. The MegaSquirt-II™ EFI controller can be configured to use any of these 'pickups'. There is much more information here: pickups.

For more information on:

MegaSquirt® and MicroSquirt® controllers are experimental devices intended for educational purposes.
MegaSquirt® and MicroSquirt® controllers are not for sale or use on pollution controlled vehicles. Check the laws that apply in your locality to determine if using a MegaSquirt® or MicroSquirt® controller is legal for your application.
©2004, 2010 Bruce Bowling and Al Grippo. All rights reserved. MegaSquirt® and MicroSquirt® are registered trademarks. This document is solely for the support of MegaSquirt® boards from Bowling and Grippo.