5 Symptoms of a Bad Ignition Sensor on a Mercruiser Outboard

Do you own a Mercruiser boat engine? If so, it is essential to know the symptoms of a bad ignition sensor on a Mercruiser. The ignition sensor is a vital component in the engine; when it goes bad, it can cause several issues.

Depending on the engine’s type and age, Mercruiser bad ignition sensor symptoms might vary. If the ignition sensor malfunctions, the engine will misfire, stall, or start poorly. A bad ignition sensor may cause engine damage over time, so it’s crucial to identify and fix it immediately.

Knowing the signs of a bad ignition sensor can help you catch problems early, saving you time, money, and potential headaches. This article will discuss some signs that your Mercruiser has a bad ignition sensor.

How to Tell if You Have a Bad Ignition Sensor on a Mercruiser?

When your Mercruiser has a faulty or bad ignition sensor, you will notice various abnormalities in motor performance that can indicate a potential problem with the ignition sensor. 

Some of the signs that may indicate a bad ignition sensor include the following:

Symptom 1: Trouble Starting

One of the most common symptoms of a bad ignition sensor on a Mercruiser is trouble starting. If your boat is having trouble starting, it could be due to a defective ignition sensor. 

This could present itself in various ways, such as hard starts, stalling out after starting, or difficulties turning the engine over.

Symptom 2: Engine Stalls While Running

A bad ignition sensor could cause the engine to stall while running since it may not be sending the appropriate information to the engine’s control module. Check if a clogged fuel filter or low fuel pressure causes the problem.

Symptom 3: Missing or Weak Sparks

If the ignition sensor fails, the system may not get the required signal, resulting in weak or absent sparks. This can result in engine problems when starting and a lack of power when running.

Symptom 4: Engine Not Getting Sufficient Gasoline

This could be due to a defective spark plug, a faulty fuel pump, or an air leak. Because the engine isn’t getting enough fuel, it will run rough and won’t start.

This might also result in stalling out or backfiring. It is critical to recognize this disease as soon as possible because it can progress to more severe complications if left unchecked.

Symptom 5: Backfiring

If the ignition sensor is broken, the engine may backfire because it doesn’t get the right signals about when to fire. Check to see if the engine timing is out of sync and if the engine is running too lean or rich.


To ensure your engine works, have a trained mechanic check out and fix your ignition sensor if any of these things happen. 

The ignition sensor tells the engine control module (ECM) how fast and where the engine turns. If there are any problems, they should be fixed right away.

7 Possible Causes of Ignition Sensor Failure on a Mercruiser Outboard

The ignition sensor transmits RPM and position data to the engine control module that outboard engines need (ECM). 

Ignition sensor failure can cause engine failure, poor performance, and trouble starting. Failure of the Mercruiser outboard engine ignition sensor can be caused by the following:

  1. Switches on and off at RPM above 2000
  2. Problems with the ignition module or coil
  3. Defective fuel pump
  4. Faulty coil
  5. Wiring issues
  6. Engine grounding problems
  7. The trouble with engine timing or compression

Replacement and Repair Costs of Mercruiser Outboard Bad Ignition Sensor

A Mercruiser outboard engine’s ignition sensor replacement or repair cost depends on the model, year, location, and mechanic’s experience. However, the following is an estimated cost breakdown for a typical repair:

Parts & ServicesDescriptionsCosts(Approx.)
Ignition SensorReplacement of faulty ignition sensor with a new one $50-$250
LaborThe time and expertise required to remove and replace the ignition sensor $77 and $97 per hour
DiagnosticsCost of identifying the issue with the ignition sensor $50-$100
TotalThe total cost of the repair, including the cost of the new sensor, labor, and diagnostics $170-$450

Note: It’s also crucial to know that other issues, such as a faulty control module, corroded cabling, or a bad power supply, might cause some ignition sensor faults. Thus, to avoid wasteful spending, proper diagnosis is necessary.

Tips for Maintaining the Mercruiser Outboard Ignition Sensor to Prevent Future Failures

Maintaining the Mercruiser outboard ignition sensor ensures engine smoothness and lifespan. A well-maintained ignition sensor helps avoid costly repairs.

Here are some ignition sensor maintenance tips to keep your boating adventures going.

  • Keep the ignition sensor clean and dry to prevent corrosion.
  • Have the dealer set at the ignition timing
  • Using your wiring diagram for your ignition module is a good idea.
  • Check and replace the ignition sensor as per the manufacturer’s recommendations or when it reaches the end of its service life.
  • Check the wiring and connections for any wear or damage and repair or replace them as needed.
  • Keep an eye on the engine temperature, and ensure it operates within the normal temperature range.
  • Inspect the sensor for any damage or wear, such as cracks, breaks, or loose connections.

Frequently Asked Questions

A faulty ignition sensor may cause MerCruiser engine problems. When it fails, you’ll notice because this tiny part affects engine performance. To clarify, here are some FAQs:

What does a Mercruiser ignition module do?

It turns the ignition coil(s) on and off so the spark plugs will fire. This is essential because the engine cannot function correctly unless each spark plug is lit at the precise moment.

How long do Mercruiser engines last?

Marine gasoline engines typically last 1,500 hours before needing substantial repairs. Under the same conditions, the average marine diesel engine will run over three times that long, or 5,000 hours.

How often do you need to service a Mercruiser?

The frequency of maintaining a MerCruiser depends on its use (recreational or commercial), operating circumstances (fresh or saltwater), and engine maintenance. Mercruiser should be maintained once a year or every 100 hours, whichever comes first.

Does the ignition control module control fuel?

The ICM controls an internal combustion engine’s ignition system. Signals from engine sensors like the crankshaft position sensor and camshaft position sensor determine the ignition spark timing. Although the ICM does not directly control fuel supply, it does affect engine operation.


Obviously, the ignition sensor is critical in operating a Mercruiser outboard engine. Its failure can result in poor engine performance, difficulties starting the engine, and, in some cases, total engine failure.

To avoid ignition sensor failure, maintain the sensor clean and dry, and perform routine maintenance as the manufacturer recommends. And have the ignition system checked by a professional mechanic regularly.

If you suspect a faulty ignition sensor, you should have a skilled mechanic diagnose and fix the sensor to ensure correct engine operation. Remember that preventative maintenance and early diagnosis of problems can save you money and time in the long run.

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