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Mercury Outboard No Spark on One Cylinder – A Detailed Discussion!


Mercury outboard motors are known for their dependability and high quality. These outboards are also known for fuel-efficiency.

These outboards come in different sizes.

Despite all of the benefits, there are some drawbacks. No spark on one cylinder is common in mercury outboard.

So what to do when mercury outboard no spark in one cylinder?

If one cylinder is not sparking, swap the white and green stator wires and retest. If the problem moves to the other cylinder there is a possibility that the stator is bad.

But if there is no chance you can replace the CDMs. Continuous no spark on one cylinder indicates a bad trigger.

This was just a gist. If you have some time in hand we have got a whole article for you. So let’s jump into it.

Why does Mercury Outboard Have No Spark On One Cylinder?

Mercury Outboard No Spark on One Cylinder

First, let’s know a bit about the outboard. Usually, there are four cylinders on the mercury outboard. There is a switch box and four ignition coils on the outboard.

To find out the reason for not sparking on one cylinder follow the below steps

Step 1

You need to pull off all your spark plug wires. After you do that you have to have something to ground them.

Keep a spark tester with yourself. Now ground the spark wires.

The bottom bolt is stripped on the motor that’s why there is a cover for it. Keep the cover to the side. It will give you some space if you open up the top. Use four wing nuts to open up.

Now the actual work begins. There is black with a yellow tracer and that’s your kill switch circuit. Cut off your switch circuit.

Take off the switch box after eliminating it from the system. It’s gonna spark if your kill switch or any other stuff up in there is the issue.

You can see that your black with yellow tracer has two of them. And they are going on too. Take the tracer. Once you have turned that off, turn over the motor and watch from the front.

You can see there is a nice blue spark. If that doesn’t work you know you are all good up there. So reattach that with a switch box and then we get on to the next test.

Step 2

In this step, we will test the rectifier. Locate your rectifier first and take off two yellow wires coming from the stator.

These wires run down from the stator and go down. Pull those off and put the bolts back on leave.

Turn the yellow wires over and over again. Look right there and see if there is any spark. If there is no spark the fault is not in the rectifier or regulator.  So reattach those wires.

Step 3

No Spark on One Cylinder

There are two choices for flywheels and that’s why we pull off the top right away. You have got to see if you have a black stator or red stator. Check if they are bolted in magnets. There can be no bolt on it.

Look behind the magnets they are glued in there. Now you have to use the chart for gluten magnets. Start with resistance reading. There are different types of residences. OEM resistance has a mercury number on it.

Switch the box and go from blue to blue and white. It should be between 30-50 and 36-50 in our red to red.

Meanwhile 75-90 in red to white. Now take the meter and switch it to ohm to calculate.

Now attach the lead with the meter. Check the resistance on the screen of the meter. If it shows more than 90 that means the resistance is a little high. Now go from blue to blue and white.

The result might be way too low.

Step 4

For the final test you need a deviated adapter. It is an auto reader so it will calculate within a second. Take your leads and start off with blue to blue and white. We are supposed to get a result between 180-400 volts.

Now turn over the motor. The result might be below 180 volts when it is faulty. Now check the same thing with red to red and white.

The optimal result for this would be 25-100 volt. If the actual result is way too low, remove the red to the red and white wire.

Stator Issue Or Switch Box Problem

Now it’s time to determine if you have a stator issue or a switch box issue. Use the rubber to kind of pinch it on there.

If the voltage reading comes up you can be sure that the stator is good.

To know more about mercury outboard bad stator symptoms read this.

In that case, the switch box is bad. Now turn over the motor and see what the reading is. If the reading is between 25-100 it’s all good. Now go on to blue and white. If the reading is between 180-400 that means the stator is bad.

Now take off the flywheel and get to the stator. You are gonna need pullers for that. It will pull that flywheel off.

So this is the way to figure out the reason for no spark on one cylinder. To know about mercury optimax 115 problems give it a read.


Outboard motor for fuel-efficiency

What Would Cause No Spark In Outboard?

A faulty stator can cause no spark problem on the outboard. So when there is no spark on the outboard do check the stator. If the problem is with the stator, replace it.

Will A Bad Rectifier Cause No Spark?

Yes, a bad rectifier can cause no spark problem. If you have a weak starter motor it can get no spark with the plugs installed.

In that situation, there is no benefit of charging your battery fully. It will just become hot and you have to use the kicker to get back in.

What Does Rectifier Do On Outboard Motor?

On an outboard motor, the rectifier’s primary function is to push electricity in one direction.

For this, there are diodes in the rectifier. The rectifier should exhibit continuity in one direction if it is working properly.

What are the symptoms of a bad CDI on an outboard?

The CDI (Capacitor Discharge Ignition) is an important component of an outboard motor’s ignition system that helps to create and distribute the electrical charge needed to ignite the fuel mixture in the engine.

When the CDI is not functioning properly, the engine may exhibit a range of symptoms, including:

Difficulty starting: A bad CDI can make it difficult for the engine to start, or cause it to start and stall immediately.

Misfiring or rough idling: A CDI that is malfunctioning can cause the engine to misfire, which can make the engine run rough or stall at idle.

Poor performance: A failing CDI can cause the engine to run poorly, with reduced power, acceleration, and overall performance.

Backfiring: A bad CDI can cause the engine to backfire or pop, which can be caused by an incorrect timing of the ignition.

Stalling: A malfunctioning CDI can cause the engine to stall, especially when under load or at high speeds.

If you suspect that your outboard motor’s CDI is not functioning properly, it’s important to have it diagnosed and repaired by a qualified technician.

Ignition system components are critical to the proper operation of the engine, and a malfunctioning CDI can lead to serious engine damage if not addressed promptly.


No Spark In Outboard

Now you know about mercury outboard no spark on one cylinder.

After you find out where the problem is, the task is very simple for you. Either you have changed the stator, switch box, or trigger.

Then you’re ready to take your boat out!

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