There are many helpful uses of multimeters around your house and while many of these are typically used on your vehicle or in your home, it is also very useful for smaller engines you use including your lawnmower. If you have ever tried starting your lawn mower and pulled that cord over and over without any luck, it could mean many different things including a fault with fuel/oil, the induction coil, or the spark plug.
What you will need
- Digital multimeter that can measure resistance(ohms)
- Leather gloves
- Owner’s manual for your Lawnmower
Checks before testing the ignition coil
After eliminating things like oil and gas being present and that the cord is connected to the spark plug, wait 10 minutes after you’ve tried starting it and then try starting it again as an initial troubleshooting.
If it still wont start, before you begin testing the ignition coil, it’s important to first check the spark plug to eliminate that as an issue.
!!! Before you start the next steps, it’s important that you wear leather work gloves to protect your hands from different parts of the engine that may be sharp or spark !!!
Spark plugs often get dirty and worn down over time. If you’ve been using the same spark plug for a while, you may want to pull it out and check for different signs of problems with your lawnmower. Removing the spark plug is easy by using a socket wrench and twisting it out.
If your spark plug has some light-brown deposits on it, it means it’s normal. If you see black carbon deposits then it’s a sign that the fuel-to-air mixture is too rich and that your carburetor has an issue. Safe to say if you know you’ve had the same spark plug for the past year in your lawn mower, it’s time to change it.
You can also use a spark plug tester (purchased in most auto stores) which you can replace the spark plug with and try to pull the cord of the lawnmower to start it. If you see a spark appear in the tester, you know that the lawnmower is in good condition but the spark plug was faulty and it’s time to replace it. A spark plug tester is an easy way to check that.
Testing your ignition coil by using a multimeter
After you have ensured the spark plug is not an issue, it’s time to check on the ignition coil. Make sure you continue to wear your leather gloves through this part.
Here are the steps to follow to check the ignition coil:
- Remove the spark plug cover which is usually a rubber cord that pulls right off the spark plug easily with a little tug.
- Remove the engine cover which is on the top of your lawn mower. Depending on the type of lawn mower you are using, there may not be a cover (in the case of a riding lawn mower, the hood may already be the cover).
- Locate the engine’s flywheel which looks like a circular piece with multiple blades going around in a circle. Each engine is different so if you are unsure you should check your law mower’s user manual to determine what/where it is.
- Remove the flywheel using a wrench and then inspect the coils. The ignition coils are situated on top of the engine beside the flywheel with two ends touching the flywheel rim. One of the coil’s terminals should be shown leading to the spark plug.
- Now, set your multimeter to test resistance (ohms) by first placing the red lead into the socket which has this symbol: Ω. Then set your multimeter to measure ohms(Ω).
If you need more information on measuring resistance, check this article here.
- Touch the positive(red) probe to the metal connector inside the spark plug housing. The negative(black) probe should then be placed against the metal that extends out of the second terminal on the ignition coil.
- Allow your multimeter to measure for a few seconds until it stops fluctuating. If the meter is showing 0, your coil is no longer working and you will need to bring it in for repairs.
- On a working ignition coil, you should get a reading of between 0.5 and 1.3 ohms. If it’s below 0.5 it needs to be replaced as it will cause damage to your engine.
Why does the ignition coil break?
Typically, the ignition coil can go bad over time due to either long-term wear and tear or due to bad spark plug ignition cables. If the spark plug ignition cables are getting faulty, it will have a much higher than normal resistance which causes additional voltage to be generated by the ignition coil which causes excess heat. This in turn melts the coil’s wire insulation causing the wires to break requiring a new ignition coil.
What is an affordable multimeter to test this on?
There are many great multimeters on the market and if you’re looking for the best brand, then the Fluke brand is definitely the one to go for. The Fluke 116, Fluke 117, and Fluke 87V are some of the best on the market.
If you are looking for a good multimeter that’s a bit more affordable, then I would instead suggest the Innova 3340 which is a much better choice for DIY and home owners.
The things you can do with a multimeter is endless and you can find so many different benefits from using it that it’s no doubt one of the best devices to keep around the house. I often talk about many of these tasks that you should do yourself at home not only save you time and effort, but also to save you money.
Doing the above test may have caused you up to $50+ at a small engine shop which you could do yourself. Start saving time and money by learning these awesome multimeter life hacks.