Briggs and Stratton Ignition Coil Testing

Learn how to test a Briggs and Stratton ignition coil to determine whether or not it needs replacing.

Tools/Parts:

    • Multimeter


Step 1

Set the multimeter to the 20 k ohms setting. A working ignition coil will give a reading of between 2.5 – 5 k ohms.

Step 2

Set the positive lead of the multimeter in position where the spark plug would usually insert – ensure it has made good contact. Place the negative lead onto the metal body of the ignition coil – again ensuring it makes proper contact.

Step 3

Look for the reading on the multimeter. A reading of 2.5-5.0 kohms indicates the ignition coil is in working order. No reading indicates a broken circuit, a higher reading will cause either a weak or non exsistant spark.

 

65 Responses to “Briggs and Stratton Ignition Coil Testing”

  1. I’m confused. You set the meter on the 25 ohm range to measure 2,500 to 5,000 ohms, and then say that the coil should be between 2.5 and 5.0 ohms. Do you mean set the meter on the 25 kohm range, and the coil should be between 2.5 and 5.0 kohm (1 kohm=1,000 ohms)? That is more the range I would expect. Also, what if any reading would you expect on the kill wire that comes out of the coil? My coil reads 10 kohms but more significantly the kill wire is 0 ohms to frame, which I suspect means it is FAB. Thanks for posting this anyway – makes life easier. 🙂

    • lachlan Osmotherly November 24, 2014 at 4:06 am Reply

      Hi

      Sorry to confuse you the write up had a few errors we had not noticed. You are correct the Multimeter is set to 20 Kohms and the Reading for a working coil should be between 2500-5000 Ohms. The Kill wire should read 0 ohms to the frame and between 2500-5000 between the ignition lead.

      • Hi,

        You say here that the kill wire should read 0 ohms to the frame. I thought the kill wire was only grounded to the frame when the switch was in the stop position? I thought it would usually be infinite to the frame?

        Could you clarify?

        thanks

        • lachlan Osmotherly April 12, 2015 at 9:22 am Reply

          Hi

          The kill circuit should have infinite resistance unless it is connected to the frame. Once you connect it to the frame with your multimeter leads it will read 0 resistance.

          • Hello – sorry I’m still a bit confused with the last answer. My B&S engine has just stopped working and I’ve checked the coil and I get about 2,6kohms between the body of the coil and the HT lead connector. But, I get 0 ohms between the stop-switch connection and the coil body – which surprised me as I thought that that was the connection made by the stop-switch (ie it grounded the coil to stop the engine) – can you clarify that one again?

          • lachlan Osmotherly May 12, 2015 at 11:13 am

            Hi

            that reading is okay you should get 0 Ohms from the body of the coil to the stop switch connection. The stop switch should have no continuity when in the open position and continuity in the closed position.

  2. I have a Briggs Coil with three wires.
    http://i.ebayimg.com/images/i/270760121969-0-0/s-l140.jpg
    One is the spark plug, the other is the condenser and the third is bare copper wire, I think a ground. When I follow your instructions I’m getting no reading but if I touch the negative (-) to the copper wire or condenser wire I do. What does that tell you.

    • lachlan Osmotherly March 29, 2015 at 11:59 pm Reply

      If the reading you are getting is within the required range i would suspect the coil is okay. However i can’t be sure as i haven’t tested those particular coils before.

  3. brendan.nolan1986 April 5, 2015 at 8:58 am Reply

    I want to buy a lawn mower. Do you have any refurbished ones for sale?? A victa perhaps??

  4. Hi, the kill wire should be around haalf ohm when the killswitch is not grounded. It’s an inductance shunt. If you read open, it will keep running through the brake.

  5. will this check also tell if coil is bad when lwanmower gets hot?

    • lachlan Osmotherly July 16, 2015 at 11:59 pm Reply

      Hi

      This will not determine if the coil is failing when hot, You could put your coil in the oven at around 60 Degrees for a short time then test it at that temperature to determine if anything has changed

  6. Checking my coil, it is reading 4.94 The higher the reading near 5, would you expect less spark?

    • lachlan Osmotherly July 19, 2015 at 4:23 am Reply

      Yes a higher reading means there is more resistance to electrity flow so the spark would be weaker as you get closer to 5K Ohms

  7. So if I’m getting a reading above 5 k ohms does that mean I need to replace the coil?

    • lachlan Osmotherly August 4, 2015 at 8:58 am Reply

      Yes if you are experiencing problems relating to lack of or weak spark a reading above 5 k ohms indicates your coil is in need of replacement

  8. What if it reads below? my reads 1.9k

    • Hi

      a lower reading can indicate one of the windings in the coil has shorted causing less internal resistance, This would also cause failure of the coil.

  9. What should the resistance be to the left pole of the magneto?

    Thanks

    • lachlan Osmotherly January 6, 2016 at 1:32 pm Reply

      Hi

      Briggs and stratton only provide a range of between 2.5 and 5 K ohms as a working range for the coils.

  10. You say you have the new cool for sale on the website but I’m not finding it when I search for coils have a link? I need a coil for an old outboard and it looks to be the same unit where it slides over the stacked plates and one is bent up to hold it.

  11. The higher the number the weaker the spark.

    Thanks,
    Martin

  12. B&S engine model: 121602-0336-E1, purchased 11/22/2002. Digital voltmeter set to 20K ohms. Spark plug wire disconnected. Meter connected between spark wire cap and metal part of engine. Before starting engine it measures 4.82. Starts on first pull after priming 3 pushes on bulb. After an hour of mowing, meter reads 5.72. Engine won’t restart. Engine sets for 1 hour, meter reads 4.92. Engine started on 2nd pull. Should I conclude the magneto needs to be replaced? Once in a while I like to bag the grass, but it is such a pain if I can’t get the mower to restart after dumping the bag. I’ve been putting 3-4 caps of Seafoam in when I fill the gas tank for a year or so. New spark plug, air filter and oil changed. Thanks for your help.

    • lachlan Osmotherly June 14, 2016 at 7:09 am Reply

      From the results of your testing I would conclude that your spark is weakening as the engine warms up this would most likely be the cause of the hard hot starting issue.

      • How is it the spark is enough to keep the engine running until I shut it down? Then it won’t restart?
        Thanks for the initial quick reply.

        • lachlan Osmotherly June 14, 2016 at 10:53 am Reply

          Hi Gene

          I’m not totally certain of the reason but this type of issue does occur, It could be that it is easier to keep the engine running then it is to start the end once stopped. Thus the spark is enough while running but too weak to get the mower going again once stopped.

          • That is kind of what I was thinking. I’ll let you know how it turns out. Thanks again!

          • I made a trip to the dealer to pick up a new coil. the new 590454 measured even more cold that mine does hot. Something like 6200 ohms from frame to plug lead. They are suggesting maybe the needle is not seating properly in the carburetor. They thought maybe I should give the prime bulb a push and a half to give it a little gas, because maybe it leaks out.
            Using that theory, now that I think about it, would be flawed since after it cools for an hour it starts without priming. Next time I mow I will try priming it a bit to see what happens. I’m not holding my breath. The 6200 reading of the new 590454 coil bothers me though. Any thoughts?

          • lachlan Osmotherly June 19, 2016 at 11:12 pm

            It seems unusual that the new coil has a high reading, The recommended reading that Briggs and Stratton supply is between 2.5 & 5 Kohms. This could have changed with newer ignition coils. Trying the primer is worth a shot it could be related to the heat of the engine causing air locks in your intake piping a few presses of the primer may sort it out if thats the case.

  13. My push mower starts easily but after about 20 min it quits every time & won’t start until it cools. My neighbor said it’s a bad coil. any comments?

    • lachlan Osmotherly June 26, 2016 at 11:32 pm Reply

      Hi Rin

      This is a common Symptom of a bad coil, When the coil heats up the resistance increases causing the spark to fail until the coil cools off again.

  14. With my meter set on 20k, I get a reading of 4.77. Does that mean 4770 ohms or only 4.77 ohms?

  15. I have a B&S 5hp outboard motor (model AA0101) which doesn’t start. It is getting fuel (somewhat). I have cleaned the carb. It is getting very little if any spark. I took off the coil. I measured between the kill switch and the body and it says 0 ohms. Between the body and the HV it reads 6.5kohms. Between the kill switch and the HV it also reads 6.5kohms. I need my motor to get by boat out of the harbor, so what can I do to get it started if, indeed, it is the coil? Thanks

    • lachlan Osmotherly July 27, 2016 at 1:45 am Reply

      If the spark is weak it will be very hard to start and run your outboard, You may have a slim chance with some engine starting spray. The best option is the replace the coil and restore the spark.

      • I replaced the ignition coil with a brand new one from ereplacement parts and did a reading on the new one. The reading was the same as the old one, so either I’m not reading it correctly, or the new one is bad as well. It’s getting gas (I checked the carb bowl) and compression, but still no spark. Is there a way to check if the kill switch wires are bad, or if it will start or give spark by bypassing the kill switch? They don’t seem to be frayed or touching anything. I don’t know what else to do.

        • lachlan Osmotherly July 31, 2016 at 12:25 pm Reply

          It is unlikely that the new coil is also bad it may just be an incorrect reading, Or the coil readings are different for outboard engines.

          If you have not tried a new spark plug I would try that first, Otherwise you will need to check for continuity in all the wires & test or replace any other components in the ignition system until you find the problem.

          You can remove or disconnect the kill switch to test if it is the problem.

  16. I was initially getting a reading of 9k ohms from my original coil. I recently purchase a new coil and got around the same reading. Could there be an issue with the spark plug boot cover as I haven’t replaced this. I have replaced the spark plug.

    • lachlan Osmotherly August 5, 2016 at 3:35 am Reply

      There could be an issue within the connect from the cover to the spark plug, This is however not very common

  17. Hey everyone. I was kind of surfing this site and read all kinds of ways to test Magneto’s or electronic ignitions. I have been servicing mowers for many years, including the old breaker points ignition systems, and the easiest way I have found to test these things is by the idea of “seat of your pants technique.”
    What I propose is “not” the recommended way but, in my opinion, the quickest was to test these things. If you can stand a little shock, then here it goes.
    I first remove the boot over the spark plug then remove spark plug. This will do two things. One it will eliminate the possibility of engine accidentally starting and eliminating any compression in combustion chamber. Here is the shocking part. If your plug wire has a boot covering the connector then insert one of you fingers into the boot ant then put another finger of same hand anywhere on the block. Pull starter rope or turn on starter enough to briefly turn flywheel. You should get a decent shock, but not enough to harm you.
    If your wire does not have the boot, consider yourself somewhat lucky. Just hold the wire “close” to the block and look for a spark jumping from wire to block. May need to be in a relatively dark place to see spark

    This procedure is assuming you have pulled break release / kill handle back to the run position. If no shock, check kill switch which will, unfortunately, means removing top of engine cover.

    If you do get shock. Then ignition is good. Look elsewhere for other problems.

    • What you are saying might sound stupid but the fact is that this is about the best way to find out if anything is happening from the coil or not, especially when the spark is weak, or can’t be seen due to lighting problems, or when the wires can’t be properly secured/grounded to do the test.

      Thumbs up (grounded or not)!

  18. Hello i have an auto ranging multi meter so i cant set it to 20k but i assume its accurate as when i test my coil it reads 7.5k so my coil is bad?

    • lachlan Osmotherly August 25, 2016 at 12:47 am Reply

      Hi

      A reading of 7.5k is high and would suggest your spark is much weaker then it would be with a lower in spec reading.

  19. OK, all the resistances check out properly but I still get no spark. What next? I assume my 5 HP B &S engine must have a capacitor some where. Does this mean I have to pull the flywheel?
    Also, the 2.5-5 Kohm resistance is for one winding. What about the other? Is there a way to check its resistance?

    • Hi Howard

      This test is testing both winding’s in series, I do not know of a way to test one winding at a time at the moment. If you have not replaced the spark plug that would be the first thing. There is no capacitor unless you have a points ignition system. If you cannot get spark with a new plug & the kill switch wire is not earthed then the nest step is to replace the coil.

  20. I have a Briggs and Stratton 4.5 hp mower. No spark. Old coil read approx 4.9 ohms using analog multimeter. Ordered new coil. New coil reads 6.0 ohms right out of the box. Is this too high? Also, I noted that the curvature of the coil is not the same as the shape of the flywheel. In other words. the gap between the coil and the flywheel is not consistent as the two surfaces are not parallel to each other. Is this also a problem? Wish I could explain it better.

    • lachlan Osmotherly October 8, 2016 at 2:21 am Reply

      6 ohms may not be too high as the coil could be different to the original coil and may use different specs, It seems like the coil may not be the correct fit if the curvature does not line up correctly, It is best for it to be consistent and about the width of a business card for the air gap, You should try the coil anyway it may work if it has been sold to you as a replacement.

  21. My Briggs lawnmower has a resistor in the spark plug cap and a metal cover on the cap. Do the same ohm meter readings apply? I get no reading after the resistor. 4.5K before the resistor.

    • lachlan Osmotherly November 1, 2016 at 12:26 pm Reply

      Hi Bob

      The resistor would change the reading, However if you get no reading after the resistor it would suggest the resistor is damaged.

  22. Thanks so much for your fast reply. I plan to remove the resistor from the spark plug cap (and the steel cover) and use a resistor spark plug. This should work?? I have seen a few Briggs magnetrons and they appear to be similar except for this one with the resistor and steel cover. Is this style unusual or discontinued. Thanks again for your help.
    Regards,
    Bob Brown.

    • lachlan Osmotherly November 1, 2016 at 11:35 pm Reply

      Yes a resistor spark plug should work fine as a replacement, I have not seen one with a resistor so I suspect they are not very common

  23. The Briggs spark plug cap with the internal resistor seems to be obsolete and replaced. I have two old lawnmowers with this setup. Both mowers resistors failed. No ohm reading downstream of the resistor. I removed the resistors and all is good. Google will show this and one from NGK.
    Regards from Canada.

  24. Have had similar experience with a Briggs engine on a Craftsman mower..with kill wire removed from mower,
    1. No spark
    2. New plug
    3. Replaced coil…. new reads 6200 ohms..old reads 4800 ohms.
    4. Checked another identical new coil at dealer…reads 6000 ohms.
    5. Flywheel key checked…..ok…..wheel may be 1/16″ displaced, no more….STILL NO SPARK..magnets seem strong…..Tested with screwdriver tip.
    6. Will check will local lawnmower repair shop for used coil and compare resistance readings

    Any help to get mower running……carb has had overhaul kit installed.

    • Hi Mel

      It sounds like you have replaced most of the important parts, Coils over 5kohms may well work as the 2.5-5Kohm range is suggested for older models similar to the mower in the video, newer or different models often can have different specs. If the magnets are strong and the coil and spark plug is new then the most likely issue is incorrect too large air gap or incorrect wiring causing the coil not to work properly.

  25. Hi, I have a question. If I am getting spark in a spark tester, but getting continuity with the kill switch in both on and off positions, is that still an ignition coil issue, or fuel related? (compression test was good). This is a Craftsman Snowblower. Thank you!

    • lachlan Osmotherly December 8, 2016 at 3:12 am Reply

      Hi

      Usually in one position the off switch will ground the coil causing the spark to stop, Depending on where you are measuring you can have continuity with the switch both in the on and off positions. If you have a spark you should try putting a few drops of fuel in the spark plug hole. If the blower starts briefly it is likely to be a fuel issue. If it does not start compression may be low.

      • If the kill wire connector coming off the coil going to the primary coil is suppose to kill the engine – only when the kill wire is grounded to the engine – how can it have continuity at all times?”?? Shouldn’t matter where you measure. Remove the kill wire from the ignition coil and measure ohms from connect tab on the coil to the frame of the coil… seems if there is not sufficient resistance, the coil is grounded all the time and will not work. Is this right?

        • Push Mower Repair August 10, 2017 at 1:51 am Reply

          Hi

          The kill wire should only have continuity when connected to the engine, If you remove the coil and the kill wire then as you said it there should be no continuity between the kill wire connector and the frame of the ignition coil. If there is continuity between the connector and the ignition coil frame there will be no spark as the coil will be grounded.

  26. what should the voltage be at the spark plug when using a voltage meter to check the ignition coil output on most small engines, ie. chain saw while pulling the starter rope?

  27. Hi, just posting to say thanks for the comments here as they helped fix my Briggs and Stratton 35 Classic problems. This was my issue;

    Mower is old; 10 years +, but dry-stored, not much use each year, new fuel used every year and old drained at end of season. Oil has never been changed, but topped up once (I think). Never had an issue with it and it will usually start first time after a winter’s lay off when I need it again.

    Problem:

    Used it twice this 2017 season, no issues at all, then come to use it for the third time (and just two weeks after the last time) and it simply will not start. Tried all the following;

    -Checked fuel, tank holding sufficient, also seen to “squirt” into carb. when bulb depressed
    -Not fuel locked; removed plug and checked for excess fuel
    -Pulled up and “locked” the safety bar in place with velcro, and tried again, just in case… no improvement
    -Squirted lighter fuel into plug hole, still no response… beginning to expect spark issue
    -Find and disconnect kill switch wire, to rule that out… no change
    -tried three different plugs; original, “known working” and brand new; no change, still nothing at all
    -get wife to try and check for spark by removing plug, but keeping connected to magneto and wife holding bottom of plug to mower body (with insulated pliers) whilst I pulled cord to turn over engine; results inconclusive, but after argument and scuffle subsides (following Police intervention), 99.9% sure no spark is present

    Solution;

    Removed cowling starter cover and using help provided above, removed ignition HT-lead and magneto assembly and used multimeter to check resistance off the mower; reading of 2.74 Kohms seen, so looks good. Noticed that the magneto surfaces that “face” the flywheel magnets were quite “cruddy” with crap like dried grass(?), and so I used a piece of emery paper to clean up the surfaces, including the surface that goes “face down” where it is screwed to the body (basically, anything metal I could get to that was “black” got sanded until it shone a bit brighter).

    I checked the magnets on the flywheel and they were still strong enough to hold a screwdriver, but I noticed a smaller amount of black crud on the flywheel along this edge where the flywheel would pass the magneto, so I cleaned that off too with the same emery paper.

    With that done, I reinstalled the magneto, paying attention to the “cylinder side” / “this side out” lettering on it, and used a piece of thick-ish card as a gauge to set a gap between the flywheel and magneto (as seen on another video online), as I tightened up the bolts.

    I pulled the card free and satisfied myself there was enough of a gap (to start things off at least), and made one last check of the resistance of the magneto “in-situ” this time, and that still showed around 2.75 Kohms.

    I didn’t bother to try and check the spark and just put the plug in to see what would happen. One quick prime push and a pull and the engine spluttered and almost started, so I was pretty sure I’d sorted it.

    With another priming, and a good solid pull, the engine turned over and started immediately. I was grinning for a few moments, and stopped to tap on the Police van glass and attract my wife’s attention, and who was sitting handcuffed inside. I mouthed “look! Working now!” to her, but wasn’t able to catch her vocal reply although it looked like she was making some “F-sound” words as the Police officer restrained her, and I struggled to lip-read her.

    Of course, after a few minutes when I then released the safety bar to stop the mower, although the engine slowed due to the braking effect on the flywheel, the engine didn’t stop… because i’d not reconnected the kill-switch wire… Doh!

    Pausing briefly to glance at my wife, who was now pointing and laughing at me along with the Police Officer too, I had to think for a moment before realising that I could use the insulated pliers to pull off the plug cap and kill the engine like that, which worked fine.

    Disassembled the cowling cover again, re-connected the kill-switch wire, reassembled again, re-fired engine (still good) and checked for kill-switch by releasing safety bar, and this time the engine was killed straight away.

    So, although I can’t really understand exactly why it went from start first time to not starting between the time I stopped it last and put it away, the cause was the magneto either drifting too far from the flywheel (it was still solidly screwed in, so think this is unlikely, but…), or just too gunked up to give a decent contact “gap” to work.

    Cleaning the magneto surfaces and flywheel, and re-seating the magneto seems to have cured the issue at the moment.

    Oh, and wife gets out in 12 months. 😉

    (all the wife and police stuff was just me joking. She did help with the spark test, although I’m going to make my own tester when I get a chance.

    Regards

    James

  28. My Briggs and Stratton 16hp v twin has no spark with a good spark plug and with the multimeter set on 20k ohms the magneto reads 4.82 ohms on each magneto. Do I need New magnetos?

    • Push Mower Repair July 24, 2017 at 5:19 am Reply

      Hi Drew
      The correct reading changes depending on the coil type, For your 16hp Briggs it is most likely the reading could be different so we are unable to say if the coils are good or bad.

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