How To Test Chainsaw Coil

Are you a chainsaw user having issues with your chainsaw coil and have no idea what is wrong? If so, then you are definitely in the right place.

Testing chainsaw coil is easy, and it involves using a multimeter or multitester to test the coil. You will need to have a working multimeter in proper condition and know how to take the reading of the coil. You will have to read the correct resistance reading of the chainsaw in the manual, locate the coil on your saw, connect the positive and negative cords of the multimeter to the negative and the positive terminal of the coil in the chainsaw, and measure the resistance.

In this article, you will get to know the step-by-step instructions on how to test chainsaw coil. Continue reading to get all the answers that you are looking for.

How to test chainsaw coil

Step 1: Take care of your safety and protection

Firstly, you will need to ensure that you have put on a reliable pair of rubber gloves and eye protection. You should use insulated pliers for preventing yourself from electrocution. Moreover, ensure that the chainsaw is turned off.

The location of the ignition coil might vary from model to model of the chainsaws. In most models, it is located near the distributor. Sometimes, a plastic cover will be used in concealing the coil for safety reasons. You need to remove the cover and get access to the coil.

Step 2: Disconnect and test the spark plug

You need to disconnect one spark plug wire from your chainsaw’s spark plug. In most models, these wires go from the distributor cap to the spark plug. These wires are simple to remove, as they’re held in place by only one or two bolts.

You’ll require a set of hand tools to disconnect the wires. The engine of your chainsaw can be quite hot, so ensure that you’ve got the safety gloves on all the time. Allow your saw to sit and cool down for 15–20 minutes to prevent any serious injury.

If possible, you should test the spark plug using a spark plug tester to ensure that it isn’t damaged. You should consider attaching the spark plug tester to the wires of your chainsaw’s coil, instead of connecting the spark plug to the wires. For that, you will need to ground the alligator clips and try to crank the engine to see any spark in the tester’s gap.

The spark plug tester will help you prevent any dust, dirt, debris, or twigs from entering the combustion chamber of the chainsaw.

Step 3: Remove the spark plug

You need to remove the spark plug of the chainsaw using a spark plug, which is a special kind of wrench. You shouldn’t let any dirt, dust, or debris fall into the hole from where you’ve removed the spark plug.

Anything left inside the hole could damage the entire engine of the chainsaw, so you’ll have to keep the hole covered. You should use a piece of dry cloth for preventing anything from falling into the combustion chamber.

Step 4: Check the primary ignition circuit of the coil

Now, you will need to check the coil’s primary ignition circuit. The coil of your chainsaw features two circuits – primary and secondary. You need to connect the positive and negative leads of the multimeter to the positive, while connecting the negative terminals of the coil of your saw.

The coil of some chainsaws features a negative and positive terminal that is marked “-” and “+”. While others feature two terminals or two pins located at their connectors. The average primary resistance range of the chainsaw’s coil is between 0.4 and 2 ohms. However, you have to research the accurate primary readings of the chainsaw specified in the user manual.

If the multimeter displays a reading of zero, it’s an indication that you should replace the coil at once, as it has internally shorted in the primary windings of your chainsaw. In case the multimeter is displaying a reading above the specific level, this is an identified that you’ll also need to replace the coil as it is open.

Ignition Coil Primary & Secondary Resistance Testing

Step 5: Test the secondary circuit

Now, you’ll need to test the secondary circuit of the coil. You should connect the positive pin or terminal of the coil to the multimeter. Moreover, you should connect it to the high output terminal going into the spark plug of the chainsaw.

The average secondary resistance range of the coil of a chainsaw will be somewhere between 6,000 and 10,000 ohms. However, you should still research for the accurate secondary reading of your machine specified in your user manual.

If your multimeter is displaying a reading of zero, this is an indication that you should replace the coil of your chainsaw at once since it has short-circuited. If the multimeter displays a reading above the specified level, this is an indication that you’ll need to replace the coil of the chainsaw as it is open.

Step 6: Disable the fuel pump

You need to disable the fuel pump fuse or relay of the chainsaw before trying to crank the engine to check the spark plug of your saw. It’ll allow you to check the coil for any sparks, as the engine won’t start. For locating the fuel pump fuse or relay, you have to read the user manual. 

If you don’t remove the fuel pump fuse or relay, it’ll cause significant damage to the chainsaw as it’ll be flooded with fuel. The cylinders would be tested, and it won’t fire as there’s no spark plug.

Step 7: Crank the engine

Say that the coil in your chainsaw is working. Now, try to crank the engine. It’ll provide power to the electric system and the spark plug of the chainsaw. 

Step 8: Check for any sparks

In case you see any bright blue sparks inside the spark plug gap when you’re trying to crank the engine of the chainsaw, it’ll mean that the coil of the chainsaw is working properly.

The bright blue spark will be clearly visible in daylight. If you don’t see any sparks, it’ll mean that you should replace the coil of the chainsaw as it is malfunctioning. 

If you see an orange spark, it’ll mean that the coil of the chainsaw is supplying insufficient electricity to the spark plug.

There are three potential reasons for orange spark –

1. Faulty connection
2. Cracked coil casing
3. Weak current 

If you see no sparks at all, this is an indication that you’ve performed the test incorrectly or that the coil in the chainsaw is complete. Another reason is that one or two electrical connections might be faulty.

Step 9: Reinstall the coil

Now, you need to reinstall the coil of the chainsaw after replacing it, if needed. Insert it into the place from where you removed it, and then reconnect all the wires. Put on the plastic cover in case you removed any.

Step 10: Test the coil’s resistance

To test the resistance of the coil in the chainsaw, you will need to use a bench test. You must take your multimeter and then remove the coil from the chainsaw to get easy access to the electrical terminals. You should ensure that the engine of the chainsaw is turned off, and it has had the chance to cool down before you perform the test. Then, you should disconnect the coil from the distributor wire.

Use a wrench to remove it from its mounting. You should then connect the test leads to a multimeter by plugging them into its jacks. You should set the multimeter in its “Ohm” position. After that, you should touch the test leads together. The multimeter should read 0 ohms. Now, you’ll need to move the test leads apart.

You should note the infinite reading that the multimeter is displaying. Now, you’ll need to remove the ignition wire from the spark plug of the chainsaw. Touch one of the leads of the multimeter to the terminal of the spark plug and the other lead to the engine ground.

You should firmly press the point of the leads of the multimeter for ensuring that they are properly connected. If your multimeter is displaying a different reading, this means that the spark plug of the chainsaw isn’t working properly and requires a replacement. Remember that you shouldn’t touch the points of the leads with your naked fingers, or else the multimeter will display inaccurate readings. This happens as the readings will include the body resistance and inaccurately indicate a bad spark plug.

Step 11: Find the resistance specifications of the coil

You should now find the resistance specifications of the coil of your chainsaw. Every coil comes with its own unique electrical resistance specifications. When the reading of the coil falls outside this specified range, it means that the coil has been damaged.

Look at the reading on your multimeter. Ideally, you would get a reading of 2,500 to 5,000 ohms. This indicates that the coil’s wiring is intact and working correctly. On the multimeter, the reading of “zero” will indicate no resistance at all or perfect connectivity, whereas the reading of “one” will indicate complete resistance or no connectivity at all.

If you’re testing the coil and the multimeter shows the value “one”, it indicates that there is no connectivity at all and the coil is faulty, and it needs to be replaced at once.

Step 12: Connect the multimeter to the primary coil and then measure it

You need to position the leads of the multimeter on the poles of your chainsaw’s primary coil. The distributor of your chainsaw comes with three electrical contacts – one in the middle and one on each side. The electrical contacts might be either internal or sunken in, or they could be external or jutting out.

You should now turn on the multimeter and touch 1 lead to each one of the outer electrical connections Your multimeter will display the resistance of the coil’s primary winding, you have to record this reading. The newer models of the saw have contract configurations, which can differ from the traditional arrangements.

Step 13: Connect the multimeter to the secondary coil and then measure

Now, you need to position the leads of the multimeter on the poles of your secondary coil. You should keep one lead on one of the outer electrical contracts. After that, touch the other lead to the point where the main distributor wire is connecting to the inner electrical contact of the chainsaw’s coil.

Your multimeter will display the resistance of the coil’s secondary winding. Carefully take the reading and record it.

Step 14: Check the measurements

Lastly, you will need to determine if the measurements that you’ve made fall within the specified level of the chainsaw. Sometimes, you will find that the primary winding or the secondary winding’s reading is a bit above or below the specified range. This means that you should replace the old coil with a new one because the current one is malfunctioning, and otherwise, your saw might get damaged beyond repair.

Congratulations, you have successfully tested your chainsaw coil using a multimeter. If you don’t have the technical knowledge, or you are short on time, or you’re just not willing to put in the extra effort, you can always call a professional mechanic to perform this test.

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