Ignition Timing - Mercury MerCruiser MCM 454 Mag MPI Service Manual

SERVICE MANUAL NUMBER 23

Ignition Timing

Two items of test equipment are required: an inductive pickup timing light and a Scan Tool.
1. Connect timing light (91-99379 or similar) to No. 1 spark plug wire. Connect power
2. Connect a shop tachometer to engine.
NOTE: Before starting engine make sure the timing tab and mark, or marks, on crankshaft
damper are clean. Chalk or white paint on timing marks may help visibility.
NOTE: With engine running, set the scan tool or Marine Diagnostic Code Tool to the
SERVICE MODE and follow manufacturer's instructions. On MEFI 2 and MEFI 3 models,
engine rpm will automatically increase to a higher rpm. You do not have to increase it
manually, as stated in the following steps.
3. Connect the Scan Tool to the DLC connector (in the electrical box or on the electrical
4. Start the engine. Allow it to reach normal operating temperature.
5. On MEFI 1 Models: Manually adjust the engine throttle to 1800 rpm.
6. Aim timing light at timing tab, located on the timing gear cover and crankshaft torsional
7. Loosen the distributor clamp bolt enough to just be able to rotate the distributor with
8. Aim timing light at timing tab and recheck location of timing mark. Slowly rotate the
9. Aim timing light at timing tab and recheck location of timing mark. Repeat Step 8 until
Index Index
90-861326--1 MARCH 1999
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supply leads, if applicable, on light to 12 volt battery. Refer to Specifications - "Engine
Rotation and Firing Order," for cylinder numbering and location.
bracket) of the wiring harness.
a - Timing Tool
damper. Check the timing. Refer to "Specifications."
some resistance .
distributor clockwise or counterclockwise to adjust the timing to specified degrees.
timing is correct. Torque distributor hold down bolt to 30 lb-ft (40 Nm).
MAINTENANCE
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