Outboard Ignition Troubleshooting � Page 1A � Testing Outboards with Minimal Test Equipment
This page covers practical outboard ignition troubleshooting techniques when you do not have a full set of advanced test tools. These checks can help isolate intermittent firing, blown power packs or switch boxes, stator and regulator problems, and certain OMC and Mercury ignition faults.
Testing Outboards with Minimal Test Equipment
The following quick-check procedures apply to all engines first, then narrow down into known patterns found on certain Johnson/Evinrude and Mercury/Mariner applications. They are especially helpful when diagnosing no-spark, weak-spark, intermittent-fire, and repeated ignition module failures.
All Engines
Intermittent Firing
- A good inductive tachometer, especially a Fluke 88, can be used to compare RPM readings on all cylinders through wide open throttle. A significant difference between cylinders can help isolate a problem that may be hard to pinpoint any other way.
Engine Continuously Blows Power Packs / Switch Boxes
- If an engine repeatedly destroys ignition modules, especially on the same cylinders, replace the ignition coils on those cylinders. A coil can internally kick back and damage the module while still appearing to test good.
- If the packs lose fire on all cylinders, the stator may be sending voltage spikes into the pack and destroying it.
Visually Check the Stator, Trigger, Rectifier/Regulator, and Flywheel
- Cracks, burned areas, or bubbles in these components are signs of trouble.
- If the battery charge windings on the stator appear dark brown, black, or burned on most or all posts, the rectifier/regulator is likely shorted as well.
- Any rubbing marks on the outside of the stator can indicate upper or lower main bearing problems.
- Cracked trigger assemblies or damaged outer magnets can cause anything from misfiring to total no-fire conditions.
- Loose flywheel magnets can be dangerous, so always check the tightness of the bonding adhesive.
Rectifier / Regulators
- These can cause problems ranging from a high-speed miss to a complete shutdown.
- A simple test is to disconnect the stator leads to the rectifier and insulate them, then retest. If the problem disappears, replace the rectifier/regulator.
Johnson / Evinrude Engines
Open Type Timer Bases
- If all cylinders fire with the spark plugs removed but will not fire with them installed, try re-gapping the sensors. Refer to the OMC ADI ignition section.
Engines with S.L.O.W. Features
- If the engine will not rev up and shakes badly, the S.L.O.W. function may be activating.
- If the engine is not overheating, a failing temperature sensor may be the cause. Try replacing the sensor with the tan and white/black wire.
- Make sure all tan wires are routed as far away from spark plug wires as possible.
- Also check the blocking diode in the engine harness.
Mercury / Mariner 6 Cylinder Engines with ADI Ignitions
If More Than One Cylinder Is Not Firing
- Replace both switch boxes unless you can positively isolate the problem to the trigger.
Always Check the Bias Circuit
- Disconnect the white/black jumper between the switch boxes and check resistance from each box�s white/black terminal to engine ground.
- You should read 14,000�15,000 ohms on stock switch boxes and 9,200�9,800 ohms on racing switch boxes.
- Make sure the reading is the same on both switch boxes. If there is any bias circuit problem, both switch boxes must be replaced as a set.
No Fire on 1, 3, 5 or 2, 4, 6
- Swap the stator leads from one switch box to the other.
- If the problem moves, replace the stator.
- If the problem stays on the same cylinders, replace the switch boxes.
- If the stator is replaced and the problem still remains, try another flywheel.
No Fire on One Cylinder
- This can be caused by a bad blocking diode in the other switch box.
- Disconnect the white/black jumper between the switch boxes and retest.
- If all cylinders now fire, replace the switch box that was originally firing all three cylinders.
- To verify this, swap the trigger leads on the switch box that was firing all three cylinders originally. If the misfire moves to another cylinder, the switch box is bad.
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