Here's some fairly accurate ohm-meter checks
For OMC screw pack V-4 ignitions
A Peak-Reading Volt meter is required to test component output properly with a different test procedure, but these checks do isolate many defective parts.
Here are the ohm-meter checks you can make and a little
info on each component.
You should have already preformed the harness/key-switch elimination test by disconnecting the black wire with yellow stripe
and giving it a try. Click here for key switch elimination test
If your engine is missing, skipping, and hard or not starting it could
be caused by loose or corroded electrical connections. Check all terminals and plug-in connectors for tight, clean contact. Check all wiring for possible
shorts to ground.
A weak or inconsistent spark, or spark from only one or two ignition
coils; suspect sensor coils {under flywheel} or ignition coils.
Weak or inconsistent spark from all four ignition coils; suspect charge
coils. No spark at all; suspect power pack.
DO NOT disconnect any wires while motor is running or while ignition
switch is ON.
COILS
Ignition coils may be checked by orange coil wire substitution.
Switch one of the known good coils with the suspected bad coil !
CHARGE COILS
Charge coils may be checked by reading resistance between
brown wire attached to terminal #7 and brown/yellow wire attached to
terminal #8. Correct resistance is 555-705 ohms.
There must also be
infinite resistance between either lead and ground. Stator assembly
must be renewed if charge coils are defective.
SENSOR COILS
Two sensor coils (1 and 2) are used to trigger ignition
at each cylinder. Sensor coil 1/3 controls ignition for cylinders 1 and
3 while sensor 2/4 controls ignition for cylinders 2 and 4. Sensor coils
may be checked by disconnecting the white/black and black/white lead
wires from terminal #2, #4, #9 and #12.
Resistance between the leads of sensor coils 1/3 or sensor coil 2/4
should be 6.5-10.5 ohms.
Sensor coil wires should also be checked for a short
to ground. Defective sensor coils are not renewable separately. Replace
complete timer base.
STATOR AND TIMER BASE ASSEMBLY Stator and timer base may be serviced
after removal of the flywheel.
Stator assembly is under the flywheel and secured to the power
head by four screws.
The timer base may be removed after the stator by
loosening the four screws and then spin clips to the outside edge.
When reassembling unit, make certain that wiring does not hinder
free movement of timer base or be close enough to come into contact with flywheel while running.
Check flywheel key so flat side of key is
parallel to center line of crankshaft; taper in, flat side out. Tighten flywheel nut
to 100-105 ft.lbs. torque.
IGNITION TIMING
Connect a power timing light to No.1 (top) cylinder
spark plug wire.
Timing pointer should align with appropriate degree mark on
flywheel with motor running at full speed in gear.
Stop engine and turn
spark advance stop screw if timing is incorrect.
Tunning screw one full
turn in/out is about one degree.
Specs below are for V-4 screw pack motors
Your boats correct timing should be noted under motor cover or in owner's manual.
MODEL ------------------- Degrees BTDC
85 hp
1973, 1974--------- 28
1975,1976, 1977-------- 26
115 hp
1973, 1974-------- 26
1975, 1976------- 24
1977---------- 28
135 and 140 hp
1973, 1974 -------- 22
1975, 1976-------- 20
1977---------- 28
Coils fire with spark plugs out but not in:
Check for dragging starter or low battery causing slow cranking speed.
DVA test stator and timer base. Check for broken wires and terminals: Especially check inside the rubber Amphenol plug-in connectors.
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