Chrysler 300M, Dodge Interpid. Manual - part 81
INSTALLATION
(1) Install capacitor and tighten nut.
(2) Attach electrical connector to capacitor.
(3) Install the negative battery cable.
KNOCK SENSOR
DESCRIPTION
The knock sensor threads into the cylinder block.
The knock sensor is designed to detect engine vibra-
tion that is caused by detonation.
OPERATION
When the knock sensor detects a knock in one of
the cylinders, it sends an input signal to the PCM. In
response, the PCM retards ignition timing for all cyl-
inders by a scheduled amount.
Knock sensors contain a piezoelectric material
which constantly vibrates and sends an input voltage
(signal) to the PCM while the engine operates. As the
intensity of the crystal’s vibration increases, the
knock sensor output voltage also increases.
The voltage signal produced by the knock sensor
increases with the amplitude of vibration. The PCM
receives as an input the knock sensor voltage signal.
If the signal rises above a predetermined level, the
PCM will store that value in memory and retard
ignition timing to reduce engine knock. If the knock
sensor voltage exceeds a preset value, the PCM
retards ignition timing for all cylinders. It is not a
selective cylinder retard.
The PCM ignores knock sensor input during engine
idle conditions. Once the engine speed exceeds a
specified value, knock retard is allowed.
Knock retard uses its own short term and long
term memory program.
Long term memory stores previous detonation
information in its battery-backed RAM. The maxi-
mum authority that long term memory has over tim-
ing retard can be calibrated.
Short term memory is allowed to retard timing up
to a preset amount under all operating conditions (as
long as rpm is above the minimum rpm) except WOT.
The PCM, using short term memory, can respond
quickly to retard timing when engine knock is
detected. Short term memory is lost any time the
ignition key is turned off.
NOTE: Over or under tightening affects knock sen-
sor performance, possibly causing improper spark
control.
REMOVAL
The sensors screws into the cylinder block, directly
below the intake manifold.
(1) Remove intake manifold plenum refer to the
Engine section.
(2) 2.7L Remove the passenger side cylinder head,
refer to the Engine section.
(3) Disconnect electrical connector from knock sen-
sor (Fig. 12) or (Fig. 13).
(4) Use a crows foot socket to remove the knock
sensors.
Fig. 12 KNOCK SENSOR 2.7 L
1 - KNOCK SENSOR
Fig. 13 KNOCK SENSOR 3.5 L
1 - CYLINDER BLOCK
2 - KNOCK SENSOR
LH
IGNITION CONTROL
8I - 7
IGNITION COIL CAPACITOR (Continued)