Ignition Coil Resistance Chart For Small Engines
2-stroke and 4-stroke small combustion engines that power lawn mowers, chainsaws, grass trimmers, leaf blowers and other outdoor equipment have an ignition coil. Learn how to test one with this ignition coil resistance chart.
The ignition coil on a small engine is responsible for providing sufficient current directly to the spark plug to generate spark. When it’s not working properly, the engine will not run.
Many small engines, including from Koehler, Briggs and Stratton and Honda, have a single cylinder and one ignition coil. If your small engine has two cylinders, it may have two ignition coils, one for each cylinder.
Ignition Coil Resistance Chart Use
If you are interested in learning how to test a small engine ignition coil these are the steps you need to take, I’ve included an ignition coil resistance chart below to reference during testing.
The easiest way to tell how many cylinders your small engine has is to count the number of spark plugs it has, it will have one per cylinder. At the other end of your spark plug wires will be an ignition coil, it looks something like this.
Note: Current flow through point B of the coil on the resistance chart is directional. If your negative lead is attached to point B of the coil, your multimeter should give an infinite reading to points A and C. If your positive multimeter lead is touching point B you will get a reading to points A and C.
Make sure you connect the right lead to each section, as shown by the + and – in the top left corner of this ignition coil resistance chart.
How to Check an ignition coil for spark
The easiest method to test a small engine coil for spark is to remove the spark plug and, with the ignition coil still attached, ground the plug to the engine and turn the engine over a few times.
This will allow you to visually check for spark.
Alternatively, an inline spark testing tool and/or a digital multimeter can be used to perform an ignition coil test. More on those methods below.
If the engine has spark you will know the ignition coil is good. But what if the engine doesn’t have spark? Or you want to test the replacement before installing it? Read on.
The problem with the most common testing methods are that they don’t narrow an electrical problem down to the coil itself. They test the entire system including the plug, coil, wires and flywheel together, but any single component can be faulty.
If you aren’t sure where the spark plug is located on your machine this small engine part location guide can help you find it.
How to Properly Test a 2-stroke Ignition Coil
- Remove the coil assembly
- Inspect for signs of coil damage
- Measure coil winding resistance with a multimeter, as follows.
The ignition coil base (A) is held in place with two bolts, remove these with a 10 mm socket wrench. A stop wire (B), often called a kill switch, connects to the coil, unplug it. The main wire (C) has a boot on the end and connects to the spark plug, unplug it. (See ignition coil diagram above for location of A, B and C).
To gain access to an ignition coil, you will typically need to remove the engine cover. Follow the spark plug wire to get a general idea of where it is located, and only remove what is needed to gain access.
When checking for frayed wires, pay attention to signs of rodent chewing on any wire cladding (rubber wire covering). Damaged cladding can lead to corrosion of the wire inside.
I recommend you temporarily connect the boot to a spark plug to see if the connection is secure. If it’s loose, electricity will not pass as easily, which might cause intermittent loss of spark. Disconnect the spark plug from the coil to proceed.
Checking Ohms on a small engine ignition coil is easy. I made this simple ignition coil resistance chart to help you better understand where to connect your multimeter’s leads and to know what readings to look for.
Resistance Testing a Small Engine Ignition Coil
- Set your multimeter to measure resistance (Ohms) and select the 20k resistance range.
- Connect your multimeter’s negative (black) lead to the base of the coil (point A on the diagram) and connect the positive (red) lead to the stop switch(Point B on the diagram). A reading of between 2k and 18k Ohms is generally good.
- Move the positive (red) lead to the connector inside the boot (Point C on the diagram). Your multimeter should now measure a 2k to 18k Ohm reading.
- Connect your negative (black) lead to the stop switch(B on the diagram) and test points A and then point C with the other lead. Neither should give a reading, if they do the stop switch is faulty (grounded).
Important: As you can see on the chart, the stop switch is directional. You will not get a reading when measuring from B to C but reversing the leads and testing from C to B does result in a high Ohm reading. Check with your manufacturer’s specifications for exact readings.
For safety purposes, never run a small engine without the ignition coil stop/ground wire connected, you may not be able to stop the engine if you do. I hope this helped you understand how to test a coil on your lawn mower and other small engines.
How can I find exact ignition coil resistance specs?
To find manufacturer specs for any engine component, find the engine model number stamped on the engine itself and look that up. Engine model numbers are different from the model number of the equipment itself.
How can you tell if an ignition coil is bad?
The easiest way to determine ignition coil condition is to test with a multimeter. If you get a reading of no resistance (short) when resistance is expected or, alternatively, you get an infinite resistance measurement when only some was expected, the coil is likely defective.
How does a two-stroke ignition coil work?
A typical 2-stroke engine has magnets mounted to one side of the flywheel which are aligned with the ‘top dead center’ position of the combustion stroke. As these magnets pass in front of the ignition coil, an induction charge is produced and sent to the spark plug.
Does a 2-stroke have timing?
All engines require ignition timing, however, 2-stroke small engines that power outdoor equipment typically have a magnet built into the flywheel to control ignition timing. This type of timing is not adjustable, a working coil will create a spark every time the magnet passes.