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MS1-Extra

MegaSquirt This Cylinder Mode with
Trigger Return Set Up

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.

First set up MegaTune to help you time the distributor. Set the center LED on the MegaSquirt front panel to show the state of the IRQ-1 inside MegaSquirt.

In these instructions, the ignition sensor is located on a movable plate to position the sensor for This Cylinder mode while maintaining the correct alignment for the rotor.  

Caution:
For your safety, you must disconnect power from the coil to prevent a spark.

With the distributor ignition wired to MegaSquirt, coil disconnected and ignition on:

  1. Set the crank at 20º BTDC at cylinder #1
  2. Rotate the distributor so the rotor arm points towards the correct contact (#1 cylinder) in the distributor cap. Fasten the distributor. Alternately locate the distributor in its normal pre-MegaSquirt location to align the rotor with the high voltge towers.
  3. Fix/fasten the distributor.
  4. Set the crank at 10º BTDC (or your engines static timing) at cylinder #1.
  5. Rotate the advance plate with the sensor in the direction of shaft rotation until the LED just turns ON.
  6. Rotate the advance plate back in the opposite direction until the LED just turns OFF again.
  7. Fix/fasten the advance plate. This fixes the Return Trigger at 10º BTDC (or static timing).
  8. Turn engine backwards until middle LED turns ON and then back OFF
  9. Turn engine forwards until middle LED just turns ON
  10. Measure the angle BTDC (+/- 5 degrees is good enough) at the crank. This is the Trigger Angle. This angle must be 50º to 90º at the crank and 10º greater than the max advance.
  11. Test your handywork. Turn the crank from near 90º BTDC in the direction of rotation. The center LED should go ON at approximately 50º to 90º BTDC and come back OFF at 10º BTDC . At this point the rotor should point to cylinder #1 tower.
  12. If the trigger angle is less than 50º BTDC then either use the Time Based cranking, or modify your distributor.
  13. Enter measured angle (50º to 90º) in Trigger Angle. This need only be an estimate. You will adjust this dynamically with a timing light later.
  14. Enter 10 (or engine static angle) in Cranking advance Angle. If you are using dwell control make sure that the number you enter in Cranking advance Angle matches the physical angle of the Trigger return or the dwell will be incorrect during cranking..
  15. Enter 10 for Fixed angle (This forces the running advance to be 10º BTDC)
  16. Turn off ignition and connect ignition coil
  17. Start the engine
  18. Adjust the Trigger angle entry until the timing light is at 10 degrees (This corrects the estimatied Trigger angle)
  19. Set "Fixed angle" to -10
  20. This completes the setup for this Cylinder distributor ignition

Example settings for This Cylinder mode with Trigger Return. Trigger Angle greater than 50º determines This Cylinder mode. The Spark Output Inverted selection depends on your install and is not dependent on the choice of This/Next cylinder mode.


 

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