Knock Sensor Settings - MegaSquirt MS3-PRO User Manual

7.3 Ignition Settings 7 ADDITIONAL ITEMS: BEYOND BASIC FUEL AND IGNITION CONTROL
• Distributor type pickup, such as HEI, TFI, or EDIS (although the last is not a distributor, the
MS3-Pro will see a similar signal.). Noise filtering is often useful here. A typical setting would
be crank tach period masking with 1ms and 30%.
• Wheel decoder and other more advanced installs. Noise filtering may be useful on some
installs. Due to the multi-toothed input signal the rejection time periods need to be set far
smaller. e.g. on a V8 with distributor at 6000rpm, the time between tach pulses is 5ms. A 36-1
wheel on the same engine gives a pulse every 0.6ms (600us). Using too large a filter time will
filter out the real signal.

7.3.7 Knock sensor settings

Note: While this is a fairly good setup as far as knock sensing goes in a race ECU, getting
OEM like levels of knock protection generally requires grenading a few motors on the dyno to
get it dialed in perfectly. This can provide an extra layer of protection, but never use knock
sensing as your only spark tuning tool!
Spark knock is the sound of abnormal combustion in an engine. Once combustion in a spark-
ignition internal combustion engine is initiated by a spark, the flame front is designed to spread
from the spark plug and travel across the combustion chamber rapidly and smoothly. As the flame
front propagates across the chamber, the remaining unburnt air-fuel mixture can ignite spontaneously
(auto-ignites) before the flame front arrives, due to the increasing pressure and temperature in the
combustion chamber. When this occurs, there is a sudden jump in the pressure in the cylinder. This
causes in the characteristic knocking or pinging sound. It is most common at low-mid rpms and high
load, such as ascending a hill in too high a gear.
Prolonged heavy knock is likely to cause severe and permanent engine damage and must
be avoided.
It is a common misconception that engines make most torque just before knock. In reality, there
isn't much of a connection between the knock threshold and the timing that makes best torque. A
knock resistant engine may start losing power well before the onset of knock, while a knock limited
engine may have the point where it makes best power past the knock threshold (and not safe to reach
without higher octane fuel) Ideally, set timing on a dyno to achieve maximum brake torque (MBT)
timing. Even with a well tuned engine, factors such as fuel octane, intake air temperature, coolant
temperature, engine age and condition, air/fuel ratios, air density, altitude and humidity and others
can push the engine from a safe condition to borderline knock or worse. The knock control system is
a safety measure designed to retard timing under these conditions and safeguard the engine.
The MS3-Pro contains an internal module that can process one or two knock sensors. It also
allows input from an external module that gives an on/off, "knock" or "no knock" signal. The knock
sensor inputs use dedicated wires intended for connecting directly to a knock sensor. External mod-
ules would use the digital input wires instead.
There are two main types of knock sensor. Resonant and wideband sensors. The resonant
sensor is tuned to a particular frequency and is only likely to work on an engine with a very similar
bore size. (Bore size determines "ping" frequency.) The wideband sensors give a lower voltage output
but operate over a wider frequency range, and can usually be applied to different engines.
DIYAutoTune.com MS3-Pro manual version 1.036, firmware 1.3.4, 6/10/2015 Page 161