How To Detect Bad Mercruiser Ignition Sensor? (Explained)

The Mercruiser ignition sensor located in the distributor is responsible for sending low voltage pulse to the ignition module whenever the sensor wheel passes through the sensors gap.

However, a bad ignition sensor interrupts the total systemic flow in the ignition system.

Therefore, let’s learn and understand the symptoms that indicate a bad ignition sensor:

What Sign You Should Look For To detect Bad Ignition Sensor?

When your Mercruiser has a faulty or bad ignition sensor, you will notice various abnormalities in motor performance such as missing/weak sparks or triggers, trouble in starting, power lacking, or even idling and stalling.

One of the most common signs that most people experience is the missing spark which causes the engine to fail. 

What Are The Symptoms Of Bad Mercruiser Ignition Sensor?

Symptoms to identifying a bad ignition sensor are usually related to the following mentioned and explained indications:

Missing/ Weak Or Intermittent Spark:

The Mercruiser ignition system has an upgraded electric sensor, which typically sends a low voltage pulse to generate the ignition trigger on the module.

But when the sensor stops acting correctly, it will cause a missing spark on the ignition system, or you might notice a weak or intermittent spark that is forcing your motor to fail.

Sometimes consumers experience wrong timing issues where the spark starts at the incorrect timing and eventually leads to the piston failure as well.

Engine Not Firing, Backfires, Or Misfires & May Lose Power:

When your outboard is not starting as it supposes to or struggling, that means there is some issue, and you should inspect it as soon as possible.

There can be different reasons behind engine performance failure in outboard, but one of the potential reasons can also be fault ignition sensor.

The bad ignition sensor can cause the engine to backfire or misfire after warming up. You may also experience that your motor is losing power.

Since the bad sensor causes no or weak spark on the ignition system, the engine also fails to start and takes more time than usual.

Engine May Perform Erratically, Starts Hard Or Rough:

When the electric sensor on your Mercruiser ignition system turns faulty, your motor may start running erratically or not maintaining the steady flow while running.

Sometimes, you may notice that your outboard is visibly struggling, especially after sitting from a run condition. Also, you might experience that engine is not starting at all.

When you have any fault in one of the ignition system parts, that gradually affects the total performance flow and leads to hard or rough starting or abruptly failing while in acceleration.

These symptoms are the easiest to recognize when you have a bad Mercruiser ignition sensor, which caused the major problem you have been experiencing.

How Should You React If You Detect Bad Or Faulty Mercruiser Ignition Sensor?

To prevent further damages, as soon you detect any of the symptoms that I have mentioned earlier, follow the below mentioned easy steps to fix the problem:

Diagnosis With Voltmeter:

If you notice any sign of a bad ignition sensor, first, connect your voltmeter negative lead to the positive lead (the white or red terminal wire in the distributor) and your engine ground.

Now check the voltmeter reading whether the reading displays 12 volts or a different result.

Remember, the reading is supposed to show 12 volts in there.

Investigate Presence Of Any Spark:

If your voltmeter reading reveals as I have mentioned earlier (12 volts), the next thing you need to do is removing the coil spark wire from the distributor.

After removing the coil spark wire, connect it to a spark gap tester to the ground. Now, you need to remove the white or green (whichever you have in your distributor terminal) lead from the distributor terminal and turn on the ignition switch.

Then, strike the white or green lead to the ground to investigate any presence of spark there. If you see any spark, you need to replace your ignition sensor.

Replace The Ignition Coil Or Ignition Amplifier:

If you see no spark in there, most probably the problem is in the coil. Therefore, add a new ignition coil, and do the same test again to see whether any spark appears or not.

Now, if you still cannot see any spark there, you need to change the ignition amp.

After replacing the ignition amplifier, the problem will be solved unless you have any other technical issue.

If Voltmeter Reading Does Not Show 12 Volts, Do As Mentioned:

If your voltmeter reading displays a different result, then look at your distributor terminal to find either white or red wire and disconnect that wire.

Now, check again to see whether the results change and show 12 volts this time. If you can see 12 volts now in the reading, replace the ignition system sensor inside the distributor cap.

If still cannot see 12 volts, that means your ignition amplifier is shot so, replace it.

Is Replacing Mercruiser Ignition Sensor Typically Expensive?

Technically, the cost of replacement may vary depending on two key facts: the damage level and whether you will be taking a professional help or will be doing the entire investigation and replacement task by yourself.

In general, Mercruiser ignition sensors are available at a reasonable price so that mass consumers can easily afford them, and labor costs will not be too high either.

How Often Should You Replace The Ignition Sensor?

Technically, you do not have to replace the ignition sensor frequently, but if your ignition sensor has turned bad or faulty, replace it as soon as possible.

Also, follow your service manual instruction for accurate maintenance guidelines.

However, Mercruiser suggests that consumers should do the required servicing every twelve months.

Final Thoughts

When you have a bad Mercruiser ignition system sensor, it can gradually damage the whole ignition system’s performance flow, which will eventually damage the motor too.

Therefore, be notified and well-informed about core symptoms to detect the problem beforehand.

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