MerCruiser 4.3L No-Spark


My MerCruiser 4.3 L V6 engine cranks but will not start up and run. I know people say that every engine requires spark, fuel, compression/air and timing to fire and begin to run.

I am sure I have sufficient fuel supply and my mechanic did a compression test on the motor a few months back and said the results were fine. So I am guessing I have no spark?

What should I check if the ignition is not generating spark or weak spark? My motor is a MCM 4.3 Liter LX Alpha I.

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Johnny Abraxas 3 years 2021-02-10T02:05:41+00:00 0 Answers 2245 views Beginner 1

Answers ( 3 )


    No Spark

    The factory service manual for this model engine contains a troubleshooting guide. It lists possible causes of no spark for conventional ignition systems and thunderbolt IV HEI ignition system. This is what it says…

    No Spark – Conventional Ignition

    • Check for moisture on the ignition components. Spark plug leads or distributor cap arcing.
    • Damaged electrical wiring, loose electrical connection or dead battery.
    • Faulty ignition switch. The MerCruiser engine may run in start position and loose spark in the running position.
    • Faulty shift interrupter switch.
    • Tachometer has shorted. Disconnect the tachometer and try to start the engine again.
    • Ignition timing incorrect. This is often the case when the engine may crank over hard, try to run backwards or backfire.
    • Ignition resistor wire or bypass wire faulty.
    • Ignition points burned, dirty or gapped incorrectly.
    • Fouled, bad spark plug, improperly gapped or cracked porcelain.
    • Faulty spark plug wires. Faulty insulation, cut wires or boot not seating.
    • Distributor cap or rotor is dirty or cracked.
    • Bad coil.
    • Condenser.

    No Spark – Thunderbolt IV HEI Ignition

    • Wet ignition components.
    • Bad battery, loose electrical connections or damaged wiring.
    • Faulty ignition switch.
    • Faulty shift interrupter switch.
    •Shorted tachometer (unplug the tachometer and try again).
    • Ignition timing.
    • Faulty, worn, damaged or improperly gapped spark plug.
    • Damaged spark plug wires.
    • Distributor cap is cracked or dirty.
    • Ignition components malfunction. Test components.
    • Engine synchronizer (if equipped) connected in series on purple ignition wire (only applies to dual engine). It should be connected directly at coil terminal, or parallel circuit.

    [table id=21 /]

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