6.0/8.1L Electronic Ignition 4B - 3
MEFI 4 - PCM
Electronic Ignition (EI) System Description
Ignition System Overview
The ignition system consists of the following components
or circuits:
• The 8 ignition secondary wires
• The 8 ignition coils
• The 8 ignition control (IC) circuits
• The camshaft position (CMP) sensor
• The camshaft reluctor wheel
• The crankshaft position (CKP) sensor
• The crankshaft reluctor wheel
• The related connecting wires
• The engine control module (ECM)
To properly control ignition timing, the ECM relies on the
following information:
• Engine load, manifold pressure or vacuum
• Atmospheric, barometric, pressure
• Engine temperature
• Intake air temperature, if applicable
• Engine speed (RPM)
The ignition control utilizes the following to control spark
timing functions:
• The 24X signal - The 24X crankshaft position
sensor sends a signal to the ECM. The ECM
uses this signal to determine crankshaft position, or
engine speed.
• The 1X signal - The 1X camshaft position sensor
sends a signal to the ECM. The ECM uses this
signal to quickly determine what cylinder to fi re the
ignition coil on.
• The ignition control (IC) circuits - The ECM uses
these circuits to trigger the ignition coils.
65872
The crankshaft position (CKP) sensor is a magneto
resistive type sensor. The CKP sensor works in
conjunction with a 24X reluctor wheel. The reluctor wheel
is mounted on the rear of the crankshaft. The 24X reluctor
wheel uses 2 different width notches that are 15 degrees
apart. This pulse width encoded pattern allows cylinder
position identifi cation within 90 degrees of crankshaft
rotation. In some cases, this can be achieved within 45
degrees of crankshaft rotation. The reluctor wheel also
has dual track notches that are 180 degrees out of phase.
This design allows for quicker starts and accuracy. The
CKP sensor also outputs a 4X signal for spark control,
tachometer output and fuel control. All CKP signals are
output as a digital waveform.
Crankshaft Position (CKP) Sensor and Reluctor
Wheel
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