Briggs coil tests bad, but works good

16 years ago

While troubleshooting and tuning a 1990 Briggs 12hp L head engine, I checked resistance of coil secondary circuit as explained on the Briggs & Stratton website.

It showed an open circuit (infinity) when it should be 2500 to 5000 ohms. Engine starts and runs good though. Using the Briggs spark tester shows good and consistant spark when starting and running. Briggs says it has internal break of the high tension lead, poor attachment of spark plug terminal, or improper mating of the high tension lead to the coil.

I checked two more good running engines which include a 12.5 hp and 8hp Briggs. The 12.5hp showed an open circuit, while the 8hp showed the correct resistance.

Should I be concerned with the two coils that test bad on two of the engines, although they start & run OK, or just run them till they quit sparkin?

Sort by:Oldest

Comments (8)

mownie
16 years ago
Well......if you want to be "text book" correct, the 2 coils that show infinity in the secondary circuit are "defective". But that calls for an explanation. Consider that, in operation, the secondary circuit (High tension, meaning high voltage POTENTIAL) conducts voltages ranging upwards of 20,000 volts. This "High tension" is capable of jumping an air gap or passing through a break in insulation if a convenient ground is touching the insulation. On the other hand, your Ohm meter uses maybe 3 volts to check that same circuit for continuity. 3 volts simply WILL NOT jump an air gap or a broken conductor. A good analogy would be to try using an Ohm meter to "test" a spark plug. So the answer is: You may have tested a coil with a break in the secondary circuit, but the spark is strong enough to jump the break and still have enough left to fire the plug (or the spark tester). The testing of the coil secondary with an Ohm meter will not determine if that coil will fire or not. It will only determine if ANY breaks in the conductor exist.
don_1_2006
16 years ago
Two coils show open but work properly. Rather than the coils I would question my meter. I would run the coils until they quit.
Related Discussions
Testing a coil with DMM
Q
Comments (26)
sfhellwig: No Problem Dude ! I can see that you are apparently getting the run around by your local Repair Facilities and are feeling the frustration. Since you are the Originator of this Thread no foul in expanding the Coil Trouble Shooting Criteria lol . I hate when Threads are Hijacked . If you follow what Baymee has advised for Safety (Bail & Torquing Specs) You should not damage the Bonded Brake Liner or Damage the Flywheel by over-tightening . If you do not have a Torque wrench use a normal 3/4" drive ratchet with 3/4" till snug unless you are a Gorilla no foul . If you feel a Small brass hammer is to evasive utilize a Fibre (Plastic) face mallet . Follow my or Tomplums advice and you will have the Flywheel of asap without incident ! I have removed two lawnmower and 3 Chainsaw Flywheels in the last month and only used 3 finger puller on the one chainsaw which was 40 yrs old it req'd the penetrating oil overnight soak since it was galled on pretty bad . Patience and gentle tapping & prying allowed removal without any thread damage . Hey don't fret $30-$60 I have seen some Coil / ignition modules go for $130+ . Sad that your Repair Agent is such a deadbeat , I have picked up used dealer units for a third of original price which outlasted the Original Mowers lol . Anyhow all the Best keep us posted and Welcome to the Site .
...See More
Lawnboy ignition coils are going bad
Q
Comments (25)
Just to update this thread with a little info useful to some Lawn Boy users in this depressed economy. The older F engine coil module 683215 /683080 can be used to replace the Duraforce engine 684048, 684049, 92-1152, 99-2911, 99-2916 coil. It takes just a few minutes of grinding and filing modifications to the coil legs and one of the mounting bosses on the block. The engine starts and runs perfect with them so the timing must be very close to the same if not dead on. I have never compared the 2 with marks and a timing light but suspect there is no difference. I have recycled numerous modules from old dead F troop soldiers to newer Duraforce units. They are open to run modules as well so there are no wiring issues to work around.
...See More
testing a coil
Q
Comments (15)
Since your engine is from the late 1980's and is fitted with a Magnetron coil, you can't test it by measuring coil resistance. The electronics and connections to the windings are all encapsulated in plastic. I understand that only a Graham or Mercotronic tester will work. But have no first hand knowledge of them. Usually a coil substitution is the best way to troubleshoot a Magnetron. Works well if you have a "goodie box" with a lot of take offs. However if you don't another coil, you'll spend about $40 or so for a new one. My suggestion would be to reattach the coil and gap properly. Do not connect the kill wire. It should be a push-on connector (or maybe flying lead). Then remove both sparkplugs. Using either a test plug, or a sparkplug opened to .060 see if the spark will jump the plug. You need to gournd the plug to the engine while someone else cranks the engine for you. Try on both spark plug leads. If you get spark to both leads, you have a kill switch or interlock problem. If no spark at this point, you've got a bad coil.
...See More
How to test an ignition coil
Q
Comments (5)
Basically, you can take the condensor OUT of the circuit and then test for a spark. If you get no spark with the condensor removed, the armature is bad. Condensors fail in 2 ways. They can short out, in which case it will kill the spark made by the coil and the plug will not spark. They can go open, in which case you will experience very short life of the ignition contact points. You need to give the kill wire a really close inspection (if there is one) to make certain it has not grounded out.
...See More
redneckjim
Original Author
16 years ago
Mownie, A good explanation and analogy. It makes more sense to me now. This was just one of those questions that bugged and nagged me as to WHY it should work. Thanks for setting my mind at ease.
mownie
16 years ago
You just might be a redneck if.............nevermind. I have run into the same issue before concerning....spark plug cables. I have routinely tested some "high tension cables" that showed infinity, and yet would still fire a plug. However, placing those "graphite core" cables back into service would sometimes show complete failure a few weeks or months later (engine mis-fire). I am certain that a few other folks have run into this "quandary" also. I have no concerns about your Ohm meter (unless it's battery power supply is nearly dead). If your batteries could be worn out, put in a new set and repeat your tests.
mownie
16 years ago
Oh yeah! I second the motion made by don 1 2006, "Rum 'em til they quit."
bill_kapaun
16 years ago
Which range did you use on the Ohm Meter?
If your meter is set on Rx1, it's probably going to show infinity (or close).
redneckjim
Original Author
16 years ago
Ohm Meter is working fine. Zeroed it out and used at a couple of ranges from Rx100 to Rx1k. Like I said, the coil on the 8hp engine showed good ( about 3600 ohms ).
mownie
16 years ago
I think you demonstrated very well the limitations of an Ohm meter for testing certain aspects of "the secondary circuit".

Briggs coil tests bad, but works good

Comments (8)

mownie

don_1_2006

Related Discussions

redneckjim
Original Author

mownie

mownie

bill_kapaun

redneckjim
Original Author

mownie

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

Briggs coil tests bad, but works good

Comments (8)

mownie

don_1_2006

Related Discussions

redneckjimOriginal Author

mownie

mownie

bill_kapaun

redneckjimOriginal Author

mownie

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

redneckjim
Original Author

redneckjim
Original Author