there are 2 systems in the book, FSM.
DIS (there is no timing at all , it's fixed by the ECU) end story.
now the 1st quote
Turn the ignition switch OFF.
Disconnect the pin-in-line connector (SPOUT connector) near the TFI module.
Start the engine and measure the voltage, at idle, from the
SPOUT connector to the distributor base. The reading should equal
If the result is okay, the problem lies within the EEC-IV system.
If the result was not satisfactory, separate the wiring harness
connector from the ignition module. Check for damage, corrosion or
dirt. Service as necessary.
Measure the resistance between terminal No. 5 and the
pin-in-line connector. This test is done at the ignition module
connector only. The reading should be less than 5 ohms.
If the reading is okay, replace the TFI module.
If the result was not satisfactory, service the wiring between the pin in-line connector and the TFI connector.
if the above fails, the ECU can not control spark. timing.
underhood VECI label is specific to YOUR truck and should be used if it differs from another source
now the next quote 2
This procedure should not be used as a periodic
maintenance adjustment. Timing should only be set after the distributor
has been disturbed (removed and re-installed) in some way. If problems
are encountered setting the initial timing with this procedure and no
mechanical causes are found, follow the spark timing advance check
procedure found later in this section.
Do not change the ignition timing by the use of
a different octane rod without having the proper authority to do so.
Federal emission requirements will be affected.
Locate the timing marks on the crankshaft pulley and the front of the engine.
Clean off the timing marks so that you can see them.
Mark the timing marks with a piece of chalk or with paint.
Color the mark on the scale that will indicate the correct timing when
it is aligned with the mark on the pulley or the pointer. It is also
helpful to mark the notch in the pulley or the tip of the pointer with a
small dab of color.
Start the engine and allow it to run until it reaches normal operating temperature.
NEVER run an engine in a garage or
building without proper ventilation. Carbon monoxide will quickly enter
the body, excluding oxygen from the blood stream. This condition will
cause dizziness, sleepiness and eventually death.
DO NOT allow the alligator clip to accidentally
ground to a metal surface while attached to the coil connector as that
could permanently damage the ignition coil.
Once normal operating temperature has been reached, shut the engine OFF.
Firmly apply the parking brake and block the drive wheels. Place the transmission in P(A/T) or NEUTRAL(M/T, as applicable).
Make sure heater and A/C, along with all other accessories are in the OFF position.
Connect an inductive timing light, such as the Rotunda
059-00006 or equivalent, to the No. 1 spark plug wire, according the
tool manufacturer's instructions.
Connect a tachometer to the ignition coil connection using an
alligator clip. This can be done by inserting the alligator clip into
the back of the connector, onto the dark green/yellow dotted wire.
A remote starter must NOT be used to start the
vehicle when setting the initial ignition timing. Disconnecting the
start wire at the starter relay will cause the ignition control module
to revert to Start Mode timing after the vehicle is started.
Reconnecting the start wire after the vehicle is running WILL NOT
correct the timing.
Disconnect the single wire in-line SPOUT connector which
connects the control computer (usually terminal 36) to the ignition
control module. This will prevent the electronic ignition from advancing
the timing during the set procedure.
Using a suitable socket or wrench, loosen the distributor
hold-down bolt slightly at this time, BUT DO NOT ALLOW THE DISTRIBUTOR
TO MOVE or timing will have to be set regardless of the current
Start the engine (using the ignition key and NOT a remote
starter to assure timing will be set correctly) and allow the engine to
return to normal operating temperature.
With the engine running at the specified rpm, check the initial
timing. If adjustments must be made, rotate the distributor while
watching the timing marks. Once proper adjustment has been reached, make
sure the distributor is not disturbed until the hold-down bolt can be
Reconnect the single wire in-line SPOUT connector and check the
timing to verify that the distributor is now advancing beyond the
Shut the engine OFF and tighten the distributor bolt
while CAREFULLY holding the distributor from turning. If the distributor
moves, you will have to start the engine and reset the timing.
Restart the engine and repeat the procedure to check the timing and verify that it did not change
Shut the engine OFF, then disconnect the tachometer and timing light.
and last one more quote "MARKS"
Timing marks consisting of O marks or scales can be found on the rim of
the crankshaft pulley and the timing cover. The mark(s) on the pulley
correspond(s) to the position of the piston in the number 1 cylinder. A
stroboscopic (dynamic) timing light is used, which is hooked into the
circuit of the No. 1 cylinder spark plug. Every time the spark plug
fires, the timing light flashes. By aiming the timing light at the
timing marks while the engine is running, the exact position of the
piston within the cylinder can be easily read since the stroboscopic
flash makes the pulley appear to be standing still. Proper timing is
indicated when the mark and scale are in proper alignment.
and last (open hood, look up, behold the USA fed EPA sticker
clearly stating the timing.
all 89s to present day.