How to test a chainsaw coil with a multimeter: Step-by-step

Approx Reading Time: 13 minutes

If you have problems with your chainsaw coil you can test is with using a multimeter or a multitester. We will show you what to do in 14 easy steps.

How to test a chainsaw coil with a multimeter:

Read out the correct resistance reading of your chainsaw in the user manual. Locate the coil on your chainsaw. Connect the negative and positive cords of the multimeter to the negative and the positive terminals of the coil in your chainsaw and measure the resistance. 

How to test a chainsaw coil with a multimeter: Step-by-step 1

A brief answer is convenient for those who are short of time but it will not give you the necessary details of the matter. Scroll on to read the detailed 14 step guide.

Check your coil in 14 easy steps

Step No. 1: Protection

First of all, you must make sure that you have put on a good pair of rubber gloves and eye protection. You must use insulated pliers to prevent yourself from electrocution. Make sure that the chainsaw is turned off.

The location of the ignition coil may vary from model to model of the chainsaws. In most of the models, it is located near the distributor. Sometimes a plastic cover is used in concealing the coil for safety reasons, take off the cover to get access to the coil.

Step No. 2: disconnect and test the spark plug

You must disconnect one spark plug wire from the spark plug of your chainsaw. In most models, these wires run from the distributor cap to the spark plug. These wires are so simple to remove because they are held in place by only one or two bolts.

You will need a set of hand tools to disconnect these wires. The engine of the chainsaw can be very hot so make sure that you have the safety gloves on all the time. Allow your chainsaw to sit and cool down for at least 15 minutes to prevent any serious injury.

If possible test the spark plug using a spark plug tester to be sure that it is not damaged and save potentially time later. You must consider attaching the spark plug tester to the wires of the coil of your chainsaw, instead of connecting the spark plug back to the wires. For this, you will have to ground the alligator clips and then try cranking the engine to see any spark in the tester’s gap.

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

Step No. 3: Remove the spark plug

You must remove the spark plug of your chainsaw using a spark plug socket which is a special type of wrench. Don’t let any dust, dirt or debris fall into the hole from where you have taken out the spark plug. Anything that is leftover inside the hole will damage the entire engine of your chainsaw so you must keep this hole covered with a piece of dry cloth to prevent anything from falling into the combustion chamber of your chainsaw.

Step No. 4: Check the coil’s primary ignition circuit

Now you must check the coil’s primary ignition circuit. The coil of your chainsaw has two circuits:  primary and secondary. Now connect the positive and the negative leads of the multimeter to the positive and the negative terminals of the coil of your chainsaw.

The coil of some chainsaws has a negative and positive terminal that is visibly marked – and +. While others have two terminals or two pins which are located at their connectors. The average primary resistance range of the coil of a chainsaw is 0.4 to 2 ohms, but you must research for the accurate primary readings of your chainsaw specified in your user manual.

If your multimeter displays a reading of zero, it is an indication that you must replace the coil at once because it has internally shorted in the primary windings of your chainsaw. If your multimeter displays a reading above the specified level, it is an indication that you will also have to replace the coil because it is open.

Step No. 5: Test the secondary circuit of the coil

Now you must test the secondary circuit of the coil of your chainsaw. You must connect the positive pin or terminal of the coil of your chainsaw to the multimeter. And also connect it to the high output terminal that goes to the spark plug of your chainsaw.

The average secondary resistance range of the coil of a chainsaw is somewhere between six thousand and ten thousand ohms, but you must research for the accurate secondary readings of your chainsaw specified in your user manual.

If your multimeter displays a reading of zero, it is an indication that you must replace the coil of your chainsaw at once because it has short-circuited. If your multimeter displays a reading above the specified level it is an indication that you will also have to replace the coil of your chainsaw because it is open.

Repeat step no. 4 and step no. 5 if needed.

Step No. 6: Disable the fuel pump

You must disable the fuel pump fuse or relay of your chainsaw before you try to crank the engine to check the spark plug of your chainsaw. This will allow you to check the coil for spark as the engine will not start. To locate the fuel pump fuse or relay you must read the user manual.

If you do not remove the fuel pump fuse or relay, it will cause serious damage to your chainsaw because it will be flooded with fuel. The cylinders will be tested and it will not fire because there is no spark plug.

Step No. 7: Crank the engine

Assume the coil of your chainsaw is working. Try cranking the engine now, this will provide power to the electric system and the spark plug of your chainsaw.

Step No. 8: Check for sparks

If you see any bright blue sparks jumping inside the spark plug gap when you try cranking the engine of your chainsaw it means that the coil of your chainsaw is working properly. The bright blue spark is visible clearly in daylight but if you don’t see any spark it means that you need to replace the coil of your chainsaw as it is malfunctioning. And if you see an orange spark it means that the coil of your chainsaw is supplying insufficient electricity to its spark plug.

There are three possible reasons for an orange spark: i)  a faulty connection, ii) weak current, iii) and a cracked coil casing. And if you see no spark at all this is an indication that you have performed the test wrong or that the coil of your chainsaw is completely dead, or one or two electrical connections are faulty.

Step No. 9: Reinstall the coil

Reinstall the coil of your chainsaw after replacing it if needed. Insert it into the cavity from where you have removed it and reconnect all of its wires. Put on the plastic covers if you have removed any.

Step No. 10: Test the resistance of the coil

To test the resistance of the coil in your chainsaw which is called a bench test, take your multimeter and remove the coil from your chainsaw to get easy access to its electrical terminals. Make sure that the engine of your chainsaw is turned off and it had a chance to cool down before you perform the bench test. You must then disconnect the coil from the distributor wire.

Use a wrench to take it off from its mounting. You must then connect the test leads to your multimeter by plugging them into its jacks. You must set the multimeter on its “ohms” position.

Now, you can touch the test leads together. Your multimeter should read 0 ohms. Now you can move the test leads apart.

You must note the infinite reading that your multimeter is displaying. Now you must remove the ignition wire from the spark plug of your chainsaw. Touch one lead of the multimeter to the terminal of the spark plug of your chainsaw and the other lead to the engine ground.

You must press firmly the point of the leads of the multimeter to ensure that they are connected properly. If your multimeter now displays a different reading it means that the spark plug of your chainsaw is not working properly and needs a replacement. Never touch the points of the leads with your naked fingers otherwise your multimeter will display inaccurate readings which will include your body resistance and falsely indicate a bad spark plug.

Step No. 11: Find the resistance specifications of the coil

You must find out the resistance specifications of the coil on your chainsaw. Every chainsaw’s coil has its own unique electrical resistance specifications. When the reading of your coil falls outside of this specified range then it means that the coil is damaged.

Look at the reading displayed on your multimeter. Ideally, you should see a reading of 2.5k to 5k ohms, which indicates that your coil’s wiring is intact and working properly. On the multimeter, the reading of “zero” indicates no resistance at all or perfect connectivity, while the reading of “one” indicates complete resistance or no connectivity at all.

If you test the coil and the multimeter remains at “one” it indicates that there is no connectivity and your coil is faulty and it must be replaced at once.

Step No. 12: Connect the multimeter to the primary coil and measure

You must position the leads of your multimeter on the poles of your primary coil. The distributor of your chainsaw has three electrical contacts, one in the middle and two on both sides. These electrical contacts may be either internal or sunken in, or external or jutting out.

You must now turn on your multimeter and touch 1 lead to each of the outer electrical connections. Your multimeter will now display the resistance of your coil’s primary winding, you must record this reading. The newer models of the chainsaws have contact configuration that can differ from their traditional arrangement.

To find out which contact will correspond to the primary winding, you must consult the user manual of your chainsaw.

Step No. 13: Connect the multimeter to the secondary coil and measure

Now you must position the leads of your multimeter on the poles of your secondary coil. You must keep one lead on one of the outer electrical contacts. Then you must touch the other lead to the point where the main distributor wire connects to the inner electrical contact of the coil of your chainsaw.

Your multimeter will now display the resistance of your coil’s secondary winding, you must record this reading, carefully.

Step No. 14: Check the measurements

Finally, you must determine whether the measurements that you just made fall within the specified level of your chainsaw. If you find that the primary winding or the secondary winding has a reading a little above or below the specified range then it means you must replace the old coil with a new one at once because the current one is malfunctioning, otherwise, your chainsaw will get damaged beyond repair.

Congratulations! You have successfully completed the test of your chainsaw coil using a multimeter. If you have no technical knowledge, or you are short of time, or you are not willing to do the extra effort, just call a professional mechanic to perform this test for you.

Frequently asked questions (FAQs):

1. What maintenance should I perform on my chainsaw on a regular basis?

You must ensure that the chain and the bar of your chainsaw are getting enough oil. You must check the chain of the saw for any visible damage, in its links and rivets. If you find any stiffness or wear in the links or rivets of the chain then you must replace it immediately.

You must sharpen the chain regularly. Check its condition and tension. You must also check the drive sprocket for wear and tear and replace it when needed.

You must clean the starter unit’s air intake ports of your chainsaw regularly. You must also clean its air filter regularly. Each week you must file off any burrs from the edges of the bars.

Each week you must replace or clean the spark arrestor screen from the muffler of your chainsaw. Each week you must clean the carburettor and replace it if needed. You must check the hose of the fuel tank of your chainsaw for any damage and replace it on a monthly basis.

Once a month, you must empty the fuel tank and clean it completely from inside. You must also empty the oil tank of your chainsaw and clean it completely from inside once every month. You must carefully check the cables and the connections of your chainsaw.

2. What to do if my chainsaw is flooded?

If a flooded chainsaw is your problem, no extra gas is needed. Don’t prime your chainsaw again. Your chainsaw has more than enough gas at the right place and this is the problem.

After a couple of minutes, you can pull the crank cord again with everything on, including the throttle pressed in with its interlock. Cranking a depressed chainsaw without a working interlock is dangerous without using a drop start, so ask for someone’s help.

Let your chainsaw have a break by turning it off. Flip off the on/off switch. Turn the throttle off.

Push or pull the choke to the “off” position. Remove the spark plug, pull the cord twice, then replace the plug. Now your chainsaw is reset and you can start the process of clearing its flooded engine.

Flooding is the major cause of a stalled chainsaw engine. Now that everything must have been turned off, pull the engine’s cord eight times. Then, without priming, try restarting with all systems on.

Now, set the on/off switch in the “on” position. The throttle “on” position must be turned on only as a last resort. Some chainsaws instruct you to tweak the throttle, do it if instructed. Put the choke to the “on” position. Everything must be back on.

Now that you have cleared the engine of your chainsaw from too much “liquid” gasoline and set the choke in the “on” position, pull the engine cord several times until the engine “pops” 1 time. Pop is a quick audible response and jerk of your engine without cranking. Don’t try more than 1 pop with the choke on or you risk another huge flood.

At this point: Place the choke in the “off” position.

With the choke in the “off” position, pull your engine’s crank cord once again. The engine will start in 1 or 2 pulls. Try it first, without using the throttle control.

Conclusion

To conclude this blog post, I would say that after reading the comprehensive and detailed step by step guide given above, you can easily perform a test of the chainsaw coil using a multimeter. It will help you save a lot of money, time and effort. Just make sure that you have carefully read, understood and followed the manufacturer’s instructions that came with your chainsaw.

Also, don’t forget to use proper PPE.