5.3 Ignition settings 5 SETTING UP A BASIC CONFIGURATION
5.3.1.3 GM HEI The original "High Energy Ignition" (HEI) distributors used the 4 pin module from the early
1970s. That module is fine in the breakerless distributor as designed, but is not suitable for computer timing
control. The later 7 and 8 pin modules and corresponding distributors are designed for computer control and
should be an easy swap onto earlier engines - not only are those modules intended for computer control, but their
distributors are already locked-out so no modifications are required. HEI7/8 uses three control wires to/from the
MS3Pro.
• The ’Ref’ signal from the module to the MS3Pro gives rpm and engine position information. It connects to
the white wire on the CKP In line.
• The ’Est’ signal from MS3Pro to the module controls the advance when running. It connects to Spark A Out.
• The ’Bypass’ signal from MS3Pro to the module allows the module to beneficially control its own advance
during cranking. Once the engine has been running for more than 5 seconds, the MS3Pro takes control of
timing. It connects to Spark B Out.
To enable the bypass, set GM HEI / DIS options to “GM Bypass on SpkB”. Set Ignition Input Capture to
“Rising Edge” and Spark Output to “Going High”. Set trigger angle 10 and adjust as needed.
5.3.1.4 MSD distributor based ignitions Most MSD distributors use a two wire sensor that MSD calls a mag-
netic pickup. This is called a VR sensor throughout the MS3Pro documentation, as there are other sensors (such
as Hall effect sensors) that are also magnetic, but put out very different signals. MSD Flying Magnet pick-ups also
fall into this category.
MSD ignition boxes require a grounded signal to trigger, and the regular MS3Pro spark outputs are designed to
provide voltage instead of grounds. The tach output, on the other hand, will provide ground, so it is used to trigger
the MSD box. For an MSD 6AL or similar box, connect the MSD white wire to the MS3Pro tach output pin.
• Ignition Input Capture depends on the sensor and how it is wired up. Set to whichever edge gives the most
stable signal across the RPM range. These signals typically have one good edge and one bad edge.
• Spark output needs to be set to Going High.
• Spark Hardware In Use needs to be set to Tacho Out.
MSD boxes can be run on standard dwell or fixed duty. The MSD box is effectively in control of the dwell in this
application.
5.3.2 Trigger Return
Trigger Return is a special case of Basic Trigger which can be used if you have a Hall effect distributor or optical
distributor where all the slots, shutters, or vanes are equally sized. The purpose of the "Trigger Return" mode is
to have accurate cranking timing as well as accurate running timing. It achieves this by using the signal from both
edges of a vane/slot. One edge is used for the timing calculations during running and will typically pass the sensor
at 55° BTDC or more. The other edge is used for cranking timing and must pass the sensor at the desired cranking
advance angle e.g. 10° BTDC.
Examples of ignitions that use Trigger Return include:
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 62
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