- The DIS module creates a 3X crank reference signal from the 7X magnetic pickup signal.
- A no start will result if magnetic pickup signal is missing.- Magnetic pick up signal must be at least 0.2 V AC cranking, resistance is(NNN) NNN-NNNN/strong>Ω
- The DIS module selects the coil pack to fire by using the 7X crank reference signal.
1.The magnetic pickup sends 7 pulses to the DIS module each engine revolution.
2.The DIS module sends the 3X signal to the PCM for fuel control.
3.The PCM sends an electronic spark timing (EST) signal to the DIS module when engine is in run
mode (over 400 RPM)
Magnetic Pick up Testing
A magnetic pick up responds to magnetic materials
rotating close to the pick up. Magnetic
materials with air gaps change the magnetic
field around the pick up coil which generates a
small voltage. The size of the voltage signal is
determined by several factors:
- Speed of rotation
- Distance of the air gap.
- Strength of the magnet in the pick up
- Number of turns in the pick up coil
A complete test should check for all four factors.
Our specifications give the resistance and the AC
voltage expected. Resistance testing checks the coil
for shorts or opens but not the other three factors. A
good example is a pick up that is cracked, the
resistance may be normal. The crack reduces the
strength of the magnetic field which will reduce the
size of the pick up signal. Another example is an
improperly installed pick up that does not seat well
in the holder because of grease and dirt packed into
the holder. This will cause a wider air gap and
reduce the size of the signal. All these cases are
infrequent, but that can make them harder to
identify when they do happen. The lab scope
pattern is the best test for a magnetic pick up. The
specifications give the resistance and the cranking
AC voltage that is normal for a magnetic pick up.
Starting is the most critical time because the engine
speed is low which results in a low output signal
from the pick up. The sync signal is also important
because it identifies the coil pack to fire. Noise can
appear as false sync signals.
Based on the crank pulses, the DIS module sends reference signals to the ECM which are used to indicate crankshaft position and engine speed.
This sensor protrudes into the block, within approximately 0.050" of the engine crankshaft reluctor. The reluctor is a special wheel cast into the crankshaft with seven slots cast into it, six of which are evenly spaced 60°apart. A seventh slot is spaced 10°from one of the other slots and serves to generate a "sync pulse." As the reluctor rotates as part of the crankshaft, the slots change the magnetic field of the sensor, creating an induced voltage pulse.
The ignition module will continue to send these reference pulses to the ECM at a rate of one for each 180°or crankshaft rotation. The ECM will activate the fuel injector based on the recognition of every other reference pulse beginning at a crankshaft position of 120°after top dead center.