1
TROUBLESHOOTING GUIDE FOR
CAPACITIVE DISCHARGE
(CD) IGNITION SYSTEMS
Most CD boxes operate the same way, making for
common basic test procedures. Most CD ignition
boxes have two separate triggering circuits in them.
One is for a regular points driver signal, which is a
square wave, and one for 2 wire magnetic, which is
a sine wave, and the two have slightly different
test procedures.
Before beginning any testing, start with the basics.
Using your ignition instructions as a guide, recheck all
of the connections and terminals, and make sure the
wires are routed correctly and are free from abrasions
or other damage. Some ignitions also are equipped
with indicator lights that can check the power source
and some internal circuits.
IGNITION BOXES USING SINGLE WIRE POINTS
TYPE TRIGGERING
If the box powers up but does not fire the coil and the
white wire is being used as the trigger source, the
following tests should be done:
1. With the key off, remove the coil wire from
distributor cap and get it where you can jump a
spark to the block, with a gap of about 1/2 inch.
Separate the triggering wire that connects the box
and the distributor together, the wire colors will
differ between boxes and distributor combinations,
for example: MSD, Crane, ACCEL and Mallory
boxes are white. On the Mallory Hyfire I’s to IV’s
and the new Hyfire VI (6) P/N 685, this wire is green.
Refer to your ignition’s instruction sheet to confirm
the color of the wire.
2. Turn the ignition switch to the "ON" position. While
holding the coil wire close to the engine block, tap
the white wire to an engine ground. This will trigger
the box and should fire the coil, jumping a spark to
ground through the coil wire. If there is no spark
from the coil wire and no audible snap comes from
the box, the box is bad. If you hear a snap in the
box but no fire at the coil wire, then the coil or the
coil wire could be bad and they need to be tested.
3. If the test comes out positive and the box, coil and
coil wire are working, the distributor is either not
working or is improperly wired into the system and
the installation instructions should be revisited.
IGNITION BOXES USING TWO WIRE MAGNETIC
TYPE TRIGGERING
1. With the key off, remove the coil wire from the
distributor and position the wire so a spark can be
jumped to the block, with a gap of about 1/2 inch.
Disconnect the 2 magnetic wires from the box and
lay them aside. Next take a short piece of wire and
bend it in the shape of a "U". This wire will be used
to short the 2 wires of the magnetic connector on
the box together.
2. With the key in the "ON" position, the coil wire
where you can jump a spark to the engine block,
and using the "U" shaped wire you have made up,
short the two wires in the connector of the box
together and then disconnect the shorting wire.
3. ach time you disconnect the shorting wire the box
should fire the coil and should jump a spark to
ground. If the coil does not fire then either the
magnetic circuit in the box is inoperative or the coil
or coil wire are bad. Magnetic distributor pickups
are generally 400 to 650 ohms of resistance. If it is
a crank trigger, the pickup is rated at about 80
ohms resistance.
4. With any of the larger MSD, Crane, and Mallory 7
and 8 boxes the tests are similar. The difference is
that they have a terminal strip instead of a wire
harness but have the same two circuits in them
and test as follows.
5. To test the magnetic circuit in the box simply
disconnect the two wire from the "MAG + and
MAG –" terminal on the box. Connect a short piece
of wire to one of the terminals. With the key on and
coil wire ready to jump a spark to the block, rapidly
tap the other end of the short jumper wire to the
other magnetic terminal. The box should fire
the coil.
6. If the trigger is points or Unilite then disconnect the
distributor from the box. Connect a long piece of
wire to the "Points" terminal of the box. With the
key on, rapidly tap this wire to ground and the box
should fire the coil.
(15 pages)
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