# no spark??? Need some help please....



## oncewaslost1982 (Nov 14, 2006)

Ok, working on a lawn mower for my neighbor. You know the story, ran great then just stopped. Ok, the engine is a 3.75 hp briggs and stratton vertical shaft. model and serial number 98902 0110 01 94101252. Its got a no spark condition. the flywheel magnets have some surface rust on them, so i cleaned it up to nice and shiny, also cleaned the surface at the end of the legs on the coil. from what i gather this is an electronic ignition engine. Are there other ignition components that i should be looking at as a possible trouble source? I also have check for spark using a spark plug tester that has the gap that should be jumped if you have a healthy ign. system and nothing good to report with that test also. Good strong magnetoc pull on one side of the flywheel and nothing on the other. The compression tests out at 70 psi of compression. Which should be plenty to run well right? The coil also throws 2.63 kilaohms of resistance. Is this good? Im using a digital multimeter for this test. one lead on plug wire, other to ground on engine block. It will not hit a lick. Not even with fuel sprayed into the plug hole. Also cleaned the end of the plug wire that wraps around the end of the plug as it had some surface rust too. So now it wont do anything and i dont want to look like an idiot and take my neighbors mower back not running. Can anyone help? I am mechanically inclined, i just dont have good luck with these small mower engines. Im allright on outboards, just these dang mowers. If there are any other tests that you can suggest please let me know and i will do them and post the results.


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## 30yearTech (Sep 14, 2006)

Did you try testing for spark with the kill switch lead wire unplugged??

If not then disconnect the kill switch lead wire and test it. If you get spark then inspect the lead wire all the way to the switch (at the back of the engine) and make sure the switch is also disengaging when the bail at the handle is pulled back. Sometimes the cable is bad and will pull back just enough to disengage the brake and not the kill switch, and I have seen the kill lead wire that was pinched in the cover or rubbed bare by the flywheel and grounding out the ignition.

If all this checks out and you still have no spark, then it's time to replace the module.


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## oncewaslost1982 (Nov 14, 2006)

so you are talking about the black wire that runs out from the coil to the back of the engine right? about a foot long? Lemme know if im correct on this and ill check it out.


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## 30yearTech (Sep 14, 2006)

oncewaslost1982 said:


> so you are talking about the black wire that runs out from the coil to the back of the engine right? about a foot long? Lemme know if im correct on this and ill check it out.


You are CORRECT sir!!! :thumbsup:


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## oncewaslost1982 (Nov 14, 2006)

Ok, thanks! I will check it in the morning and post the results. Would the resistance reading that i gave for the coil not have any bearing on diagnosing the problem? Just curious. I know with my outboards, mostly 1950s era johnson/evinrudes if i have between 3 and 8 kohms it means that i have a good coil. Will post results of the test with kill switch wire unplugged first thing in the morning.


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## 30yearTech (Sep 14, 2006)

oncewaslost1982 said:


> Just curious. I know with my outboards, mostly 1950s era johnson/evinrudes if i have between 3 and 8 kohms it means that i have a good coil.


The difference here is that it's not just a coil, but an electronic ignition module. The coil portion of the module rarely fails, and if it does it usually gives trouble when it's hot. What usually fails in a solid state module is the triggering device that senses it's time to collapse the field and generate the spark. You cannot test the trigger with an ohm meter, in fact you can actually destroy the trigger by sending voltage through it, so I would not recommend sending any voltage through the kill switch lead.


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## pyro_maniac69 (Aug 12, 2007)

you really can't test an coil anyways, I'm very leary on the "coil testers" the way I see it, is if the shut-off wire is off, the magnets are good, and the coil is gapped properly and you still don't have spark, should be pretty obvious that its bad. the coil testers are just $500+ way of doing normal maintence procedure the wrong way


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