5.3 Ignition settings 5 SETTING UP A BASIC CONFIGURATION
• Trigger Angle/Offset - There are three different ways this setting is used:
– In Basic Trigger and Trigger Return, it specifies the engine angle BTDC that each trigger pulse is re-
ceived.
– In Toothed Wheel, it should always be set to zero - use tooth#1 angle instead.
– In other modes, this setting can make a +/- 20 degree adjustment to the preset timing alignment.
• Angle between main and return - This is only used in CAS 4/1 mode and specifies the angular length of
each tooth.
• Oddfire first angle - For oddfire engines this specifies the angle the engine must rotate from spark A output
to spark B output.
• GM HEI/DIS, TFI, C3I options - Some distributor and related setups have a couple of extra tricks that they
use:
– Off: No additional spark outputs or cylinder identifications are used:
– GM Bypass on Spark B: On a computer controlled GM HEI or many GM distributorless ignitions, this
setting enables the "bypass" output on spark B. The bypass output allows the module to control the
timing during cranking. The ECU applies voltage to the bypass wire after startup to take control of
timing.
– Buick C3I: This uses a distributorless ignition which behaves like a GM HEI, but also includes a cam
sync signal. Used with Toothed Wheel mode instead of Basic Trigger to enable the cam sensor.
– TFI Non-Signature: Used with Ford TFI distributors where all trigger vanes are the same length.
– TFI Signature PIP: This allows you use the cylinder identification feature on Ford Signature PIP distrib-
utor, where one vane is shorter than the others. Signature PIP mode is used with "Basic Trigger" and
allows the MS3Pro to use these distributors for sequential fuel.
• Oddfire phasing - Most oddfire engines, such as the Chevy V6, use alternate long/short angles between
cylinders. Yamaha Vmax and a couple other V-twins use a paired long/long/short/short pattern. You can also
define a custom pattern with four separate odd fire angles, for engines where the odd fire sequence is really
odd.
• Skip Pulses - This tells the code how many input pulses it should ignored before attempting to match the
input pattern. The default value of 3 is suitable for most applications. Increasing this number can filter out
RPM spikes right at the start of cranking, but setting this value too high will delay startup. This setting is only
used for startup and is ignored after the engine is running.
• Ignition Input Capture - Determines if the active edge is when the voltage on the RPM input rises or falls.
This must be matched to your tach input. If it is set incorrectly you can experience timing drift with rpm or
misdirection of missing teeth on a missing tooth wheel. The tooth logger can be used to confirm polarity
is correct. Note that for compatibility across several different products in the MegaSquirt family, this name
refers to the signal at the processor, not the signal coming into the ECU. The MS3Pro’s input conditioner will
invert the signal. So if you were using a Hall effect sensor where the voltage dropped from 12 to 0 volts, the
MS3Pro will see this as a rising edge instead of a falling one. If using the Digital Frequency In pins for cam
input, the signal on the Digital Frequency In pins is not inverted.
When using a VR sensor, it’s important to set the correct edge, as one is more stable than the other. Here is what
a typical VR signal can look like:
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 57
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