7.3 Ignition Settings 7 ADDITIONAL ITEMS: BEYOND BASIC FUEL AND IGNITION CONTROL
• Tach interrupt masking - turns off input pin so pulses are not seen at all for time/percentage
This setting is similar to tach period rejection. However, instead of sensing and rejecting pulses in the rejection
time, this setting outright turns off the interrupt - it actively stops the ECU from listening during the rejection wheel.
• Time(ms) - time period to ignore for interrupt masking or period rejection. The tooth logger (see chapter 8)
can determine the lowest time value for normal sensor pulses; make sure the value you set here is at least
25% less than the measured value at maximum RPM to avoid filtering out real pulses. Be careful when using
this setting with high revving engines with high tooth count trigger wheels. If you see the MS3Pro failing to
detect real teeth at high RPM, decrease this number.
• Percentage - percentage of "tach interval" to ignore. This needs to be smaller than the percentage variation
between the largest and smallest gaps in the trigger wheel. For example, GM 7X mode has six notches 60
degrees apart and one notch offset 10 degrees from the next notch. A value of larger than 16% (10 degrees
divided by 60 degrees) could cause it to miss the 10 degree notch.
Secondary Tach settings apply to the camshaft position (CMP) input.
• Noise filter enabled - enables noise filter time on secondary/cam tach input.
• Noise filter time period - pulses shorter than this are treated as noise. Used instead of the noise filter
curve. If using a Hall effect or optical cam trigger, take the tooth width in crank degrees (or double the tooth
width in cam degrees), multiply it by 50, and divide by 3 times the maximum engine RPM. This will give you
the length of a real pulse. Then multiply this by 1.2 to 1.5 to give a safe value for the minimum noise filter
period. If using a VR sensor, you will need to measure the time between zero crossings with an oscilloscope
to determine a good value.
• Tach period rejection - ignores pulses shorter than time/percentage
• Tach interrupt masking - turns off input pin so pulses are not seen at all for time/percentage
• Time(ms) - time period to ignore.
• Percentage - percentage of "tach interval" to ignore.
7.3.6.1 Examples These should be taken as a starting point and will often need install specific tuning.
• Coil negative triggering for a fuel-only install. This requires noise filtering to eliminate the effects of coil
ringing. A typical setting would be to enable crank tach period masking at 2ms and 30%.
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 170
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