point at which the High Tension (HT) ignites the Air/Fuel mixture will be just
before pinking occurs, it would appear inevitable that at certain times and
under certain conditions knock (detonation) will occur in a std production
sensor is fitted to some management systems, the sensor being a small piezo-electrical
device that, when coupled with the Electronic Control Modules (ECM), can
identify when knock occurs and retard the ignition timing accordingly.
frequency of knocking (pinking) is approximately 15 KHz. The response of the
sensor is very fast. The best way to test a knock sensor is to remove the
knock sensor from the engine and to tap it with a small spanner.
NOTE :- when
refitting the sensor tighten to the correct torque setting as over tightening
can damage the sensor.
engine found in today's modern motor vehicle will be expected to produce a
good power output with minimum fuel consumption and exhaust emissions. Given
these factors, it is important that the mapping of the ignition advance curve
is as near to detonation (pinking) as possible. At the optimal point at which
the spark plug ignites the Air/Fuel mixture will therefore be just before
pinking occurs, it would appear inevitable that at certain times and under
certain conditions knock (detonation) will occur.
To avoid such
situations happening a knock sensor is fitted to some management systems, this
sensor being a small piezo-electrical device that, when coupled with the
Electronic Control Module's (ECM) internal knock control system processor, can
identify the frequency at which knock occurs and retard the ignition timing
frequency of knocking (pinking) is approximately 15KHz. When the ECM
compensates for knock the ignition timing as previously mentioned will be
retarded (firing later), the knock sensor will then "listen" for knock on
subsequent engine rotations and gradually release the timing retardation until
the ignition timing is back at its original mapped setting.
occur if any or a combination if the following is present :-
ratio (causing high temperature)
deposits pre-igniting the Air/Fuel mixture
the knock sensor is quite simple using either a stroboscopic timing light or
an oscilloscope. To test using the timing light, simply shine the stroke onto
the ignition timing marks and tap the block/cylinder head close to the sensor;
at this point the timing mark will move, indicating a response to the
operators actions. Alternatively, the output voltage can be seen on an
oscilloscope by connecting to the two electrical terminals and tapping the