It’s very likely that you’ll need to swap out your lawn mower ignition coil at some point during its lifespan. This is a pretty normal replacement that has to be done for all types of lawn mowers, whether it’s a push mower or a ride-on mower. But if you find that your lawn mower ignition coil keeps going bad, then this definitely isn’t normal. So, let’s look at what causes multiple ignition coils to fail and what you can do to prevent it.
What Causes Repeated Ignition Coil Failure? (The Short Answer)
The most common causes of repeated ignition coil failure are engine overheating, defective coil components such as spark plugs and cables, using incorrect parts, and poor maintenance methods. Any one of these causes, or a combination of multiple causes, can lead to your lawn mower coil failing.
What Makes a Lawn Mower Coil Go Bad (6 Possible Causes)
A lawn mower coil is made up of an iron core and copper winding tucked neatly inside the lawn mower’s ignition coil. Every time the magnet attached to the flywheel passes the coil, there is a complex reaction between the iron core, the copper winding, and the magnet that produces an electrical charge. As soon as conditions for this reaction change to less than ideal, the coil suffers. So, let’s take a look at what causes an ignition coil to go bad.
Overheating of the Engine & Coil
During the reaction inside the coil, a fair amount of heat is generated on the copper windings. To make sure the windings can cope with the heat, the copper winding is insulated to make sure that the single wire of the winding never touches itself. Now, this insulation is rated to cope with the reaction heat and the heat of the engine. Consequently, the insulation is not rated to take the added heat of an overheating engine.
So, if your lawn mower is low on oil or has a problem with cooling, then it’s probably overheating The result is the insulation loses its integrity, and the copper winding arcs back on itself. The final result is a change in the amount of charge created and the time of release. These changes lead to a burned out ignition coil.
Over Gapped Spark Plug
The charge that is created in the coil needs a method to discharge itself so that it can continue to process and make more charge safely. This is where the spark plug steps in. The spark plug on your lawn mower is basically a grounding point that this charge is attracted to.
So, once the charge gets to the end of the spark plug, it needs to arc over the gap. Now, if the gap is too big and the sparkplug is over-gapped, the arc can’t happen. This makes the coil think that more current is needed, so it increases the charge. Unfortunately, the coil isn’t designed to do this. The result is the coil produces more current and more heat. The one thing that the coil can’t handle is extra heat. So, if your spark plug is over-gapped, your coil is going to quickly burn out.
Faulty or Damaged Spark Plug
Other than over-gapping the spark plug, you might have a bad spark plug that needs changing. A bad spark plug is going to have the same effect as a poorly gapped spark plug. The coil is going to overheat because it is not able to discharge. The result is another burned out coil.
Incorrect Spark Plug
Yep, I’m afraid we’re still talking about spark plugs, but this is the last one. If you’re sitting there wondering, “why does my ignition coil keep burning out” it could be because you’re using the wrong spark plug.
Well, you’ll find that you can buy a spark plug that both fits into your lawn mower and that connects to the ignition cable/spark plug cable. But just because it fits doesn’t mean it’s the right one.
What happens if you use the wrong spark plug? Well, inside the spark plug is an electrode that the current reaches before it arcs to the ground. This electrode is designed with a specific resistance. So, if you have the wrong spark plug, the charge can’t pass the electrode. A wrong spark plug is the same as an over-gapped plug and a faulty plug. Once again, the coil produces more charge, more heat and burns itself out.
Damaged Ignition Cable/Spark Plug Cable
The reaction between the protons and the neutrons inside the coil produces an electron, the charge. This electron charge needs somewhere to go, so it heads for the spark plug. Time for the spark plug cable to step in.
Now, some years back, you would buy a coil and cable separately, but nowadays, they come as one item. Before, it was possible to get the wrong combination and mess up your coil. Fortunately, you don’t need to worry about a mix-up these days.
However, you do need to be aware of cable damage. Just like the overheating problems a spark plug can cause, a cable can do the same. If the cable is damaged or broken, the charge will back up in the coil and form the same heat damage.
Poor Practices
Let me ask you a question. Do you think it’s a good idea to test a spark plug that is attached to your lawn mower without it being grounded? Definitely not. Most of us, at some point, have removed the spark plug from the mower and pulled the starter cord to see if it’s working ok.
Well, if you pull the cord and the spark plug isn’t grounded to the mower’s engine, the coil begins to overheat. This is just the same as a bad spark plug or a broken cable. The charge has nowhere to go.
Signs a Lawn Mower Coil is Going Bad
When figuring out what makes a lawn mower coil go bad, you’ll probably be seeing a few symptoms with your lawn mower before the coil burns out. If you notice these symptoms quickly enough, you might be able to avoid another coil replacement. Here’s what to look out for.
- Poor Performance
- Lawn Mower Backfiring
- Engine Stalling
- Difficulty Starting the Engine
Is There Anything You Can Do If Your Mower’s Ignition Coil Keeps Going Bad?
Now that we have been through what makes a lawn mower coil go bad. Let’s have a look at a few things that will help you avoid another replacement. Here are some tips to help keep the coil protected.
Check the Engine Oil Level
A common cause of a lawn mower engine overheating is low oil. A lack of oil in the engine causes the metal parts to rub together and generate excessive heat. I suggest that every time you fill the gas tap, you check the oil level.
Carry Out Regular Oil Changes
As oil is used and heated, it starts to lose its cooling and lubricating abilities. This results in overheating and potential coil damage. I suggest working out an oil change schedule and make sure that you are changing your lawn mower oil often enough.
Clean Out the Air Vane Guard
When I finish using my lawn mower, I always make a point of cleaning off all the grass. I also make sure to clean out the flywheel. Located on top of the flywheel is a fan that cools the engine. It is super important to keep this clean so that the engine can cool efficiently.
Gap the Spark Plug
Gapping a spark plug is a job that a lot of people skip. I’m guessing this is because it’s not always easy to understand why it’s important. But once you know what makes a lawn mower coil go bad, I’m pretty sure you will not skip it again. So, the simple solution is to get a spark plug gapping tool and gap your plug regularly (here’s a post that explains how to gap a mower spark plug).
Double Check the Spark Plug Specification
If you look in your lawn mower manual, you’ll find out what size spark plug your mower needs. If you can’t find it, you can look online or check with your local mower store.
Using the Mower’s Off Switch
Within the electrical circuit of your lawn mower, there is a bypass for the coil. This basically grounds the coil in a different direction than the spark plug. So, if you are doing repairs on your lawn mower that require the flywheel or engine to turn, make sure the lawn mower is switched off. Disconnecting the spark plug will stop the mower from starting, but it won’t protect the coil.
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