Initial Ignition Timing Adjustments; Ignition System Diagnosis And Testing - Ford LSG 875 Service Manual

2-04
IGNITION SYSTEM
2-04
DESCRIPTION (Continued)
ADJUSTMENTS
With the ignition switch in the Run position,
primary circuit current flows from the battery,
through the ignition switch, the ballast resistor, the
ignition coil primary (BATTERY), the ignition mod-
ule (GREEN wire), and back to the battery through
the ignition system ground in the distributor
(BLACK wire). This current flow causes a magnet-
ic field to be built up in the ignition coil. When the
poles on the armature and stator assembly align,
the ignition module turns the primary current off,
collapsing the magnetic field in the ignition coil.
The collapsing field induces a high voltage in the
ignition coil secondary winding. The ignition coil
wire conducts the high voltage to the distributor
where the cap and rotor distribute it to the appro-
priate spark plug.
A timing circuit in the ignition module turns the
primary current back on after a short period of
time. High voltage is produced each time the mag-
netic field is built up and collapsed.
The RED ignition module wire provides operat-
ing voltage for the ignition module' s electronic
components in Run mode. The WHITE wire pro-
vides voltage for the ignition module during Start
mode. Bypass provides increased voltage for the
ignition coil during Start mode.
STATOR
ASSEMBLY
OF
AND
,EMBLY
B3509- 1 B
B4283-1 B
Ignition system adjustments are limited to initial
timing and spark plug gap on Duraspark II
systems.
INITIAL IGNITION TIMING
The timing marks.and their locations are illus-
trated on page 2-18.
For checking and adjusting the ignition timing
with a scope refer to the scope manufacturer' s
instructions. To check and adjust the timing with a
timing light, proceed as follows:
1.
Clean and mark the specified timing mark with
chalk or white paint
2. Disconnect the vacuum line and plug the dis-
connected vacuum line.
3. Connect a timing light to the No. 1 cylinder
spark plug wire. Connect a tachometer to the
engine.
4. Start the engine and reduce the idle speed to
600 RPM to be sure that the centrifugal ad-
vance is not operating.
5. Direct the timing on the timing marks. The light
should flash just as the notch on the pulley
lines up between the 4 and 8. Check specifi-
cations for correct initial ignition timing.
6. If the timing is not to specification, loosen the
distributor retaining bolt and rotate the distrib-
utor body until the marks are in line.
Ignition timing is advanced by counter-
clockwise rotation of the distributor body,
while clockwise rotation retards timing.
7. Tighten distributor retaining bolt and connect
vacuum hose.
8. To determine if the advance mechanism is
functioning, accelerate the engine while
watching the timing mark with the timing light.
The notch on the crankshaft pulley should
advance as engine RPM increases.
9. Disconnect the timing light.
Procedures for ignition system diagnosis and
testing are shown in the tests on the following
pages.