Mariner Mercury 105/140 JET, Service Manual

Page: 63 / 797

2A-12 - ELECTRICAL 90-824052R3 JUNE 2002
Troubleshooting Tips
1. Intermittent, weak or no spark output at 2 spark
plugs (one plug from each bank of three cylin-
ders) usually is caused by a bad TRIGGER.
2. A SWITCH BOX can also cause 2 cylinders (1
each bank) to lose spark.
3. Intermittant, weak or no spark output at 3 spark
plugs (a complete bank of 3 cylinders) usually is
caused by a bad STATOR or SWITCH BOX.
4. An IDLE STABILIZER/ADVANCE MODULE can
also cause 3 cylinders on 1 bank to lose spark.
5. Intermittent, weak or no spark output at any one
spark plug (single cylinder) usually is a bad COIL
or SWITCH BOX.
6. Loss of spark to 1 cylinder could also be caused
by a loose or broken PRIMARY LEAD between
the switch box and ignition coil or a broken or
loose GROUND lead between the ignition coil
and engine ground.
7. To more easily troubleshoot high speed ignition
problems, it is recommended that test harness
91-14443A1 be installed on outboard. This long
harness allows the mechanic to remain at the
driver’s seat while checking primary voltage, sta-
tor voltage, trigger voltage and bias voltage.
a
d
b
c
a - Plug into Meter
b - Attach to Appropriate Terminals
c - Attach to Engine Ground
d - Selector Switch
8. A heat gun, hair dryer or heat lamp can be used
to warm electrical components up (to find a
short); or components can be place in a refrigera-
tor to cool them down (to find an open). Resist-
ance values will change as a component is
heated or cooled. However, the resistance
change
should not be drastic as in a short or open
unless the component is defective.
NOTE: If using a heat device to warm electrical
components, maximum temperature electrical
components can be heated to without damage is
311 F
°
(155 C
°
).
9. Repeat failures of the same electrical component
could be caused by other electrical components.
– If one circuit in a switch box keeps failing, it
could be the result of high resistance in the
primary of a coil, primary lead between the switch
box and coil or high resistance on the coil primary
ground wire.
– If same switch box keeps failing, it could be
because of a random open circuit in the trigger.
10. When testing DVA voltage at coil primary, the
NEGATIVE test lead MUST be touching the
NEGATIVE terminal of the ignition coil and NOT
common ground.
11. Switch leads between components to isolate
problem. Example:
– If voltage is low to 1 switch box, move the RED
and BLUE stator leads from 1 switch box to the
other switch box. If voltage problem moves,
STATOR is defective. If problem does not move,
SWITCH BOX is defective.
– No spark on 1 cylinder could be ignition coil or
switch box. Moving the primary lead from 1
ignition coil to another should isolate the problem
source. If the problem follows, the SWITCH BOX
is defective. If the problem stays with the same
cylinder, the IGNITION COIL is defective.
– No spark to 2 cylinders could be a switch box
or trigger. Move a pair of trigger leads from 1
switch box to another. If problem follows,
TRIGGER is defective. If problem does not
follow, SWITCH BOX is defective.
12. Trigger Voltage can be checked with a voltmeter
set on the 20 VAC scale. Place 1 voltmeter lead
on the switch box trigger terminal and the other
voltmeter lead to engine ground. Voltage should
be present; if not, reverse voltmeter leads. If volt-
age is still not present, trigger is defective.
13. Inspect spark plug high tension leads (especially
spark plug boots) for cuts, nicks or abraisions
which can allow voltage to leak to ground.