AEM 30-6905 Universal Programmable EMS-4 - Manual (Page 231)

Page 231 of 279 EMS-4 Install and Tuning Guide_Rev 1.6
Knock Control
The Knock Sensor Cal table defines an RPM dependent threshold to filter out background
noise. Setting up this table is key to the success of knock control. Whenever the knock sensor
voltage output exceeds this table's value at the specified engine speed, it is considered to be
"real knock". The difference between the actual knock signal and this threshold value
determines the severity of the knock.
While the engine is in operation, the amount of noise from the engine will increase as RPM
increases, so our job is to determine if what the
EMS sees as “knock” is in fact knock. If we
determine that the engine is not knocking in a certain area, we can set the filter limit (threshold)
to a higher level.
There are 2 ways to use the Knock control feature on the AEM EMS. The first is passive and the
second is active.
A passive system is just to monitor, but no actions are taken to correct for a knock situation.
Many OEM manufacturers utilize passive knock systems.
An active system will take actions to correct for a knock situation. We can choose to correct our
problem three ways:

Add a percentage of fuel to the mixture

Remove an amount of timing from the engine

Add fuel and pull timing