How to Know If Harley Ignition Coil Is Bad? 6 + Signs

How to Know If Harley Ignition Coil Is Bad

If you own a Harley Davidson bike, one of the things that might bother you is the ignition coil. Many riders face issues with the coil.

However, for experts, identifying the problem is quite easy; but, it can be brain-racking for newbies or who isn’t familiar with motorbike mechanical issues.

Addressing the problem is essential to prevent further complications. I will not suggest you go to an auto repair shop to figure out the issue. This guide will tell you how to know if Harley ignition coil is bad.

Without further ado, let’s get directly into it.

What Is an Ignition Coil?

It’s a compact electrical transformer that converts low current (12-volt) into a much higher

voltage. Once the conversion is done, it ignites the fuel, and the engine starts. Furthermore, it requires 15000 to 20000 volts of electricity for a spark plug to create an electric spark to ignite the fuel.
All spark plugs have their own ignition coil. It’s either connected to the plug via wires or wirelessly placed on top of the plug.

How to Know If Harley Ignition Coil Is Bad?

When there is something wrong with the ignition coil of your beloved Harley Davidson, the bike will show specific symptoms such as –

Un-efficient Fuel Consumption

The very first sign of a bad ignition coil is that the bike will give you poor mileage. Your Harley’s ignition coil will consume more fuel than it usually does. Once you notice this issue, be sure to check the coil to find further fault.

Engine Backfires

If your Harley’s coil isn’t at a good state, the engine can backfire. It occurs noticeable more when the engine runs rich or lean. When there is more fuel than air in the engine, it will run rich. Oppositely, when the air is more than fuel, the engine will run lean.

You might also see black smoke or some unused fuel in the cylinders that exit through the muffler.

Engine Refuses to Start

One of the clear signs of a failed coil is when the engine refuses to start. Harleys’ that run on a single-coil engine will make cranking sound, but there will be no spark from the cylinders.
Bike Stalling

If your bike stalls while working, this is another sign that indicates there’s something wrong with the ignition coil. When some irregular sparks are sent to plugs from the coil, the issue occurs. As a result, the bike completely stops or refuses to start further.

Rough Idling

Malfunctioning coil also shows symptoms such as rough idling and engine jerking. When you accelerate the engine, the bike will not respond as before and hesitate to speed up. It will sound like the power is missing.

Engine Misfiring

In some cases, your Harley will misfire. Don’t panic; it doesn’t mean there’s something wrong with the engine. A lousy coil contributes to this engine misfiring issue. The engine makes a noisy sound once you start it.

Additionally, when you ride the bike at high speed, Harley’s engine will spit, jerk, and make unusual vibration. The engine also fails to start and stays in idle mode.

Engine Light On

Even though the bike is going through an issue with the coil, the engine light will still turn on in the dashboard. If you scan using a diagnostic tool, it will show code ‘P0351’, which refers to primary circuit malfunction. This is the simplest way to troubleshoot the problem.

Test to Check the Ignition Coil

You can run a test to determine the ignition coil issue. It will not take more than 15 to 20 minutes. Things you will need to perform the test – SAE wrench set and an Ohmmeter.

  • Turn off your bike and wait until the engine becomes cool enough to touch.
  • With your hands, disconnect the plug wires off the coil. You need to use an SAE wrench to unscrew the small connections.
  • Now, for reading ‘Rx1’ resistance setting, you need to set an ohmmeter. Measure the resistance of the coil on two small terminals. The reading should be within 2.5 to 3.1 ohms.
  • Now, read the ‘Rx1000’ setting. This time, you need to measure the resistance of two large terminals. The range should be between 10,000 to 12,500 ohms.
  • If any of the readings come outside the ranges, the ignition coil isn’t in a good state, and you need to replace it.
  • Again, make sure your bike is completely cool before you attempt the test. Otherwise, the meter will give you faulty reading.

How to Replace an Ignition Coil?

If you are able to detect that the problem is within the ignition chamber, you need to replace that malfunctioning part. Not all cases require replacement, depending on the severity of the damage, you will have to either repair or replace it.

When you are confident that the ignition coil is the real culprit of all the masses, you need to replace it with a new one. To do that, at first, disconnect the negative terminal on the battery, and also disconnect the cable connected to the coil.

After that, unscrew those bolts that are holding the coil and remove it. Once you get a new ignition coil, simply put the new coil at the same place and screw the bolts. Before purchasing, make sure the coil is compatible with your Harley’s engine.

Why Does a Coil Fail?

As the engine stays hot, sensitive internal parts find it challenging to cope up with it. The same thing goes for the ignition coil. Due to intense heat and vibration of the engine, things inside the ignition chamber are prone to break the windings and insulation of the coil.

In most cases, damaged cables and wires cause a worn spark and electrode gaps to plug together, which end up in coil failure. Besides, when the output voltage of the coil rises to a high level, it causes short circuits and burns around the insulation.

Final Words

People freak out when their beloved motorbike goes through any mechanical failure. For those who own Harley Davidson, the craziness is even more. The issue with the coil isn’t rare in this bike. After reading the article, you have an idea of how to know if Harley ignition coil has gone bad.

Run the regular maintenance of your bike. If the coil is too damaged to repair, consider getting a compatible coil for the ride.

Resources & References


Hi, I’m Adam Vachon, an avid learner and working in the product marketing niche for the last few years. The problem I faced when marketing products for manufacturers made me interested in starting GearsLoft.

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