Page 288 - REPOWER REFERENCE GUIDE (2020)

Ignition Timing
MerCruiser Ignition Timing Procedures

IMPORTANT: Refer to the appropriate MerCruiser Service Manual for engine ignition timing specification.
Breaker Point Ignition
1. Connect the timing light to the number 1 spark plug lead.
2. Start the engine and operate it at its normal idle speed.
3. Aim the timing light at the timing tab, located on the timing gear cover and crankshaft harmonic balancer.
4. Adjust the timing by loosening the distributor clamp and rotating the distributor as required to set the timing to specification.
Thunderbolt IV Ignition System

1. Connect the timing light to the number 1 spark plug lead.
2. Start the engine and operate it at its normal idle speed.
3. Aim the timing light at the timing tab, located on the timing gear cover and crankshaft harmonic balancer.
4. Adjust the timing by loosening the distributor clamp and rotating the distributor as required to set the timing to specification.
Thunderbolt V Ignition System
1. Connect the timing light to the number 1 spark plug lead.
2. Before turning the key, connect a jumper wire between a ground source and the timing lead (purple with white trace).
3. Start the engine and allow it to reach its normal operating temperature. Operate it at its specified idle rpm.
4. Adjust the timing by loosening the distributor clamp and rotating the distributor as required to set the timing to specification.
5. Stop the engine. Remove the jumper wire from ground and the timing lead.
3.0 L EST Ignition System

1. Connect a timing light that is equipped with an advance dial to the number 1 spark plug lead.
2. Start the engine and verify the engine is operating at normal temperature in neutral.
3. For Quicksilver 3.0L (4 degrees BTDC) set timing light to 30 degrees.
4. Bring the engine speed to 2800–3000 RPM in neutral.
5. Adjust the timing by loosening the distributor clamp and rotating the distributor as required.
6. Bring the timing mark to 0 degrees on the timing tab found on the harmonic balancer then tighten the distributor clamp,
slowly bring the engine back to idle, stop the engine, and remove the timing light.
EFI and MPI, MEFI I, MEFI II, and MEFI III

1. Connect the timing light to the number 1 spark plug lead.
2. Start the engine and operate it at its normal operating temperature.
3. For MEFI I and II systems: Bring the idle RPM up to 1500. (Not required for MEFI III.)
4. Connect a DLC timing tool (91‑805747A2) or DDT (using version 2.0 Cartridge 91‑803999) in service mode.
5. Adjust the timing by loosening the distributor clamp and rotating the distributor as required to set the timing to specification.
6. Remove the timing tools from DLC, allow the engine idle to stabilize, and stop the engine.
GM and Mercury Distributor MPI Systems 2002 and up
1. Verify that the engine is at number 1 cylinder TDC compression stroke.
2. GM (HVS) distributor: Remove the cap, loosen the distributor clamp, and align the rotor tang to the number 8 (V8 engine)
or number 6 (V6 engine) marking on the distributor housing.
3. Mercury distributor: Mark the distributor housing inline with the number 1 spark plug wire terminal, remove the cap, loosen
the distributor clamp, and align the rotor tang with the mark made on the distributor housing.
4. Tighten the distributor clamp. ECM controls ignition timing from this point.

Page 8C-2 © 2019 Mercury Marine 90-8M0149179 eng NOVEMBER 2018