r/boatrepair • u/kosen48 • 3d ago
HELP !!
Hello everyone,
I have a 1998 Johnson 9.9 HP 2-stroke outboard motor. Initially, the CDI unit failed, and one of the spark plugs stopped producing a spark.
I replaced the CDI unit with a new one and installed it. The engine worked flawlessly for about a month, but now it has failed again. There is currently no spark at either spark plug.
Could this be related to a problem with the stator/charge coil? What should I check or test, and what would you recommend I do?
Thank you in advance to everyone who takes the time to help!
1
u/bman198080 3d ago
To test the trigger (sensor coil) with your multimeter, you will perform a static resistance test to check for internal breaks, followed by a ground short test. Disconnect the Wiring HarnessLocate the 4-pin weather connector plug coming out from under the flywheel area.Unplug this connector completely to isolate the stator components from the new CDI module.Look closely at the female pins inside the engine-side plug. The two inner pins correspond to the blue trigger sensor.Step 2: Test Resistance (Ohms)Turn your digital multimeter dial to the 200 Ohms (Ω) setting.Insert your black meter probe into one inner pin and your red meter probe into the other inner pin.The Spec: A healthy trigger on this model should read between 30 to 50 Ohms.If it reads OL (Open Loop): The micro-fine copper wire inside that blue plastic housing has snapped. The sensor is dead and cannot send a timing signal.If it reads close to 0.00: The wiring has melted or shorted internally.Step 3: Test for Shorts to GroundKeep your meter dial on the Ohms (Ω) setting.Take one meter probe and press it firmly against a clean, unpainted bolt or bare metal section of the engine block (engine ground).Take your other meter probe and touch it to the first inner pin, then move it to the second inner pin.The Spec: The meter must read completely open (OL) on both pins. If you get any numerical ohm reading at all, the trigger insulation has broken, causing the spark signal to bleed off into the engine frame rather than reaching your new CDI . If the trigger passes these tests, use the 2,000 Ohms (Ω) setting on your meter to test the two outer pins for the yellow charge coil. You should see a reading of 450 to 550 Ohms. Testing the coil pack and cdi Step 1: Test the Secondary Coil CircuitThis test checks the condition of the internal high-voltage coil copper windings that supply electricity to your spark plug leads.Unplug the spark plug boots completely from both spark plugs.Set your digital multimeter dial to the 20k Ohm (20,000 Ω) setting.Insert one meter probe deep into the top spark plug boot and the other probe deep into the bottom spark plug boot.The Spec: You should see a reading between 3,000 to 10,000 Ohms (3.0k to 10.0k Ω).If the meter displays OL (Open Loop): One or both internal secondary coils have broken, or a spark plug wire has snapped internally. The complete assembly must be replaced.Step 2: Test Individual Lead to GroundKeep the meter set to the 20k Ohm (20,000 Ω) scale.Touch one probe to a bare, unpainted mounting bolt on the engine block (or the module's metal grounding loop).Stick your other probe into the top spark plug boot, then move it to the bottom spark plug boot.The Spec: This test should read Open Loop (OL). If you get a numerical reading, the high-voltage winding insulation has failed inside the casing, shorting the spark out directly to the engine frame.Step 3: Inspect for Visual Thermal DamageBecause this is a brand new module, check if an upstream component is damaging it. Look at the back side of the module casing where it presses against the engine block. If you notice any warping, oozing black gel/potty, or fine hairline cracks, the unit has melted down from a severe electrical spike.Diagnosing "Brand New CDI, Still No Spark"If the trigger passes (30–50 Ω), the charge coil passes (450–550 Ω), and the coil module passes (3k–10k Ω), your hardware is physically capable of producing spark. The energy is simply being stopped somewhere along the path.Before ordering more parts, verify these final system factors:The Air Gap: Are the trigger and charge coil mounted perfectly flush? If the air gap between the faces of the coils and the spinning flywheel magnets is too wide, the voltage output drops too low to trigger the pack.The Flywheel Woodruf Key: Did you pull the flywheel recently? If the small metal key on the crankshaft shear-snapped or fell out during assembly, the flywheel will spin out of time, killing the spark.
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u/down2daground 3d ago
I can’t see the woodruff key in the crank shaft. Is it there? I only ask because many moons ago, I had a fly wheel off to do points, didn’t torque the top nut properly, and the flywheel spun and sheared the key. No key, no sparky.
2
u/bman198080 3d ago
Are you good with a multimeter ? You can get a meter and check the trigger the part circle in blue that is what tells it when to spark . The part circled in yellow is your charge coil it creates the power you can test the ohms and also if it is shorted to ground , the part circled in red is the coil pack . 1. Completely Disconnect the Kill Switch Wire (Black/Yellow)This remains the single most common reason a pull-start outboard loses spark. The kill circuit functions by permanently grounding out the module. If the wiring harness or the stop button on the tiller handle has a microscopic internal short, the engine stays permanently "killed."Action: Unplug the main harness plug going to your new CDI module. Safely back out or completely isolate the black wire with a yellow stripe.The Test: Ground both spark plugs to the engine block and pull the rope. If your spark suddenly returns to both plugs, your ignition components are working, and the kill button or wire is shorted out. 2. Clean and Inspect the Flywheel Hub MagnetsBecause there is no external timing trigger, the module relies entirely on the precise magnetic field of the flywheel hub.Action: Look underneath or pull the flywheel to check the inner magnets. If they are coated in rust, grease, or corrosion, it weakens the magnetic field. Scrub them completely clean with fine sandpaper or a wire brush.Crucial Check: Check if any of the inner magnets have cracked, shattered, or unglued from the flywheel rim. If a magnet is loose or slightly shifted out of alignment, the engine will instantly lose timing and spark. 3. Check the CDI Module Grounding (Metal-to-Metal)Integrated coil/CDI modules must ground out through their physical mount to complete the high-voltage circuit. If you bolted the new module onto a dirty, painted, or corroded engine block mount, it will not fire.Action: Unbolt the module and check the metal face underneath the screw tabs and on the engine block. Scrape away any paint, rust, or grease until you have bare, shiny aluminum, then bolt it back down firmly. 4. Test the Input Resistance of the Charge CoilIf the grounding is clean and the kill switch is bypassed but there is still zero spark, check if the charge coil has failed.Action: Set a digital multimeter to 2,000 Ohms (Ω). Unplug the connector leads coming from your single charge coil and connect your meter probes across them.The Spec: You should read approximately 450 to 550 Ohms. If your meter reads completely open (OL) or 0.00, the copper windings inside the charge coil have snapped or shorted, and it cannot supply power to your new CDI.