Someone gave me a used push lawnmower with a Tecumseh 4-stroke engine. It has no points or condensor under the fly wheel, so I assume that means it has electronic ignition.
Is there a clear way to test the ignition coil/assembly to see if it is good or not?
I get no spark, afaict, using an inline neon spark plug tester.
Am I correct in thinking that repairing the ignition coil assembly will be next to impossible? And that buying a new one will cost more than any push lawnmower that is probably 10 years old is worth?
Meirman
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I had a situation something like this recently, when I was repairing a neighbor's lawn mower. It wouldn't start and I couldn't see a spark from the plug.
What I did was to hold the plug in my hand and pull the rope.
It was _obvious_ that there was juice coming through. :-)
I didn't have any trouble getting carb parts (in stock no less) for a 6HP Tecumseh almost 40 years old. The parts were cheap.
You can test the coil yourself to a certain extent. Coils have three leads, one of them being the spark plug wire. The resistance between the two non-plug leads should be pretty low - a few ohms. The resistance thru the spark plug lead to either of the other leads will be fairly high, but not infinity.
This isn't a full test, but if it fails it, it's bad for sure.
A small engines repair place may well have a "proper" tester which is capable of proving the coil good.
[Our small engines night course teacher has a "real tester". Got to play with it last night.]
Repairing a truly dead ignition coil is virtually impossible.
One of the few things you can repair is cracked coatings on the winding (_not_ the wire insulation, but the outer weather shield). [make sure it's dry, and then coat it with RTV.]
Ignition coils aren't very expensive, you'll also find them pretty universal between Tecumseh engines of even remotely similar vintages. The link below says "These are just a few Tecumseh Ignition/Electrical Parts".
formatting link
example, lists several Tecumseh coils from about $25 to $45. A lawn mower probably uses the cheap one.
In alt.home.repair on Fri, 27 May 2005 14:05:49 -0000 snipped-for-privacy@nortelnetworks.com (Chris Lewis) posted:
Cool. That's the way I like it. I think Whirlpool washers are like that.
Thanks. I think I did measure btween 2 or all three of them, but I've forgotten the results. :) At the time I didn't know it could have electronic ignition (even though I was wondering where the points were. I'll check again.
OT, but I once had sparking from the diodes in my Amana microwave. It was Model 2. The first person at Amana parts, when I only mentioned the soudn of sparking, recommended a microwave tube. The next time he suggested it was the diodes. They were a lot less money. When I took the think apart, I saw the insulation on the wire was bad, and I just covered it with black silicone cement. The thing worked fine for another 10 years. Until the transformer failed.
I"ll check it out. Thanks
And thanks Lewis. Before electoronic ignition on cars, I was pretty good at pulling plug wires off while the engine was running, without losing control of my arm. But that skill may have been lost by now. OTOH, maybe my nerves are near death by now.
Meirman
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pull the kill wire off the coil and check for spark again, if still none then it is the coil. resistance measurements are a waste of time. isolate the component, then there is nothing else. Chip
Its been a while since I replaced an ignition assembly on a mower, but I recall that it is a very easy "remove and replace " operation and the cost of the unit isn't too huge relative to the cost of a mower.
Some random thoughts:
1) Check the electronic kill switch on the mower. Make certain that your mower knows that you "want it to run." Otherwise, you'll get no spark.
2) Make certain that you don't have a sheared woodruff key.
3) Check for proper gap between the magneto and the flywheel magnet.
4) Test resistence readings on the ignition coil. This is easy and very informative.
5) Examine, clean and/or replace the spark plug.
6) Test the coil output by inserting a nail into the spark wire boot and then hold the other end of the nail near the block while cranking the engine.
7) Test the spark plug outside of the engine by placing it against the block and testing for spark. A plug will fire more easily in the open than it will in the combustion chamber. This helps determine if you are getting any coil output.
8) Try temporarily reducing the spark gap to about 1/2 of the factory spec. This makes it much easier to get a spark from a less-than-perfect system. This is a good diagnostic. Also, an engine can be run this way, although it is a somewhat less than optimal situation. The smaller spark impacts engine timing, but not in any destructive manner. (to the best of my knowledge).
Good luck, Gideon
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Is there a clear way to test the ignition coil/assembly to see if it is good or not?
I get no spark, afaict, using an inline neon spark plug tester.
Am I correct in thinking that repairing the ignition coil assembly will be next to impossible? And that buying a new one will cost more than any push lawnmower that is probably 10 years old is worth?
Meirman
-- If emailing, please let me know whether or not you are posting the same letter. Change domain to erols.com, if necessary.
As a FYI, our "small engines instructor" says that the simplest way to test for good ignition is to "construct" a 1/4" spark gap, and you should get a reasonably fat/blue spark off it. Anything less than that indicates you're probably not getting a healthy enough spark, EVEN IF, you can see it on the much narrower spark gap on a plug.
He "constructed" this tester by taking an ordinary plug, and sawing off the threaded portion, leaving the center pin open on the end of the ceramic insulator. Then, installed a clip on a wire to ground it, and a screw to adjust the gap from the center pin to the center pin. Install the modified plug into the spark wire, the clip to a ground, and pull...
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