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 2 years 2021-02-10T02:05:41+00:00 0 Answers 1840 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.

    Applicable Models

    The information on this page is applicable to several models and years, including 1983 1984 1985 1985 1987 1988 1989 1990 1991 1992 1993.

    MCM 185R 229 CID 3.8L 6289593 – 6919655
    MCM 185MR 262 CID 4.3L 6919656 – OA483580
    MCM 185 Alpha 1 OA483581 – OB455459
    MCM 175 Alpha I OB455460 – OB773242
    MCM 4.3 Liter Alpha I OB773243 – OF000000
    Sea Ray 4.3L-2 Alpha I (See Note) OB785483 – B921276
    MCM 205MR 6919687 – OA483776
    MCM 205 Alpha I OA4483777 – OB775129
    MCM 4.3 Liter LX Alpha 1 OB775130 – OF000000
    Sea Ray 4.3L-4 Alpha I OB785981 – B922330

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