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Electronic Ignition as MegaSquirt Input

Only for use with the MS1 Extra code (MS1 - 68H908 based microprocessors)

By Philip Ringwood (daxtojeiro), James Murrey (jsmcortina) and Ken Calver (muythaibxr)

Please Note:

All of these instructions / diagrams are to be used at your own risk, like most things there is more than one way to do the same thing, what we have tried to do is to offer a method that we have tested or that others have tested for us. No warranty expressed or implied.

Use at your own risk.

MegaSquirt requires a pulse from the ignition to syncronize the fuel injection. This sync can be obtained directly from the negative terminal of the ignition coil. But when you want MegaSquirt to control the coil to take advantage of the ignition tables and dwell control (constant energy ignition) another way has to be found.

By replacing the ignition coil with a resistor, after market electronic ignitions that replace points can be used to drive the MegaSquirt input. Below left is a typical install for an after market electronic ignition. To get the signal MegaSquirt needs, disconnect the leads from the ' - ' side of the coil (leave the '+' side) and run a 470 ohm 1 Watt resistor from these leads to +12 volts. The signal to MegaSquirt comes from the output of the after market electronic ignition as shown below right. The tach lead can be left as shown or in some instances may have to be moved to the '-' connection of the coil. The resistor can be as low as 50 ohms, but the power rating must be increased.

In this setup, the timing of the distributor does not change. The coil can now be controlled by table driven advance from MegaSquirt.

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