Help checking a lawn mower ignition coil

[civhatch901]

Kohler VTwin engine would turn but not start. Checked for spark and rear cylinder had none. Pulled the ignition coil and I want to check it before throwing parts at it.

Below is the resistance table from the engine's manufacturer.

Set multimeter to 2000 ohms and:
When I test between 1 and 4 result is 000
When I test between 2 and 4 result is 000

Set multimeter to 20k ohms and:
When I test between 3 and 4 result is 10.77 (this is 10,770 OHMS?)

Based on the manufacturer specs, this would mean the coil needs to be replaced but when I check the coil that was generating spark on the other cylinder I get similar results (however, the coil is still installed on the engine- not sure that matters), so I am doubting that the test is done correctly or should I say that I am using the multimeter correctly.

 

[#18FAN]

Are the plugs wet??

 

[civhatch901]

This is a Walker mower. The plugs are nearly impossible to pull with the engine in place, at least I wasn't able to do so. I had to pull the engine out to be able to access the coils. I did check the vaccuum actuated fuel pump before removing the engine and it was pumping fuel when the engine cranked. I also tried a squirt of starting fluid and absolutely nothing changed. The mower doesn't even try to fire, it just spins.

 

[mk378]

There will be a "kill wire" (usually black) from both coils to the mower harness. Disconnect this wire and measure ohms from the mower side to ground. It should be open circuit when the engine should run, and connected to ground when the engine should stop (key off, seat unoccupied with PTO on, etc). It's called the "kill wire" because grounding it kills the ignition, and leaving it open allows it to spark. If the mower side has a path to ground with the key on, you need to troubleshoot the mower circuitry.

Another test would be to disconnect the kill wire and make the engine crank and check for spark. Generally turning the key to crank will make it crank even with the whole engine harness of small wires disconnected, if not just jump the starter solenoid.

"Trial by fire" is really the only way to test a coil, ohm tests will give a lot of false negatives (test will say coil is good, when it is actually bad).

 

[FordMan59]

If the coils are identical switch positions with them, if the other cylinder doesn't fire after the switch you've found your problem.

 

[mk378]

It would still start on one cylinder. Having both coils go bad at the same time is unlikely.

 

[civhatch901]

Let me add the engine is currently off the mower.

Before pulling it, I did check that it was getting fuel by cranking the engine and the fuel pump was doing its job.

Then I checked for spark on both cylinders one at a time with the same spark plug, one had spark the other one didn't. At that point I pulled the engine out. I was unable to remove the cover and inspect the ignition system with the engine installed on the mower.

 

[stangguy]

WOW, can't work on the ignition system , even the spark plugs without pulling the engine? For me personally I would have really been set on that mower, or I would have run away when deciding to buy. Unless it is a 10 Min job to pull.

 

[civhatch901]

WOW, can't work on the ignition system , even the spark plugs without pulling the engine? For me personally I would have really been set on that mower, or I would have run away when deciding to buy. Unless it is a 10 Min job to pull.

Took me about 1 hour and I had never done it before. Pretty sure I could do it in 30 minutes the next time around with the proper tools.

 

[mk378]

I looked at the Walker website. They don't mention ease of maintenance or service at all. It looks like an exotic sports car-- fun when it runs, but when it doesn't, forget about fixing it yourself. Go to the dealer with a fistful of money and let Tony have some choice words with it while you're not there.

 

[vw7674]

you can fabricate your own spark tester with some scrap wood, two nails set the distance a decent spark is assumed to jump (usually 3/8")
and some jumper wires to ground & to the coil output. If one coil can do it & the other can't, you've got a dying or dead one.
Happens with bikes with dual-tower output coils all the time, usual answer is to buy a pair of aftermarket Dyna brand coils.
If you go that route be sure to confirm the proper resistance impedance value you require or you'll be burning the new ones up too.

 

[civhatch901]

I looked at the Walker website. They don't mention ease of maintenance or service at all. It looks like an exotic sports car-- fun when it runs, but when it doesn't, forget about fixing it yourself. Go to the dealer with a fistful of money and let Tony have some choice words with it while you're not there.

They are 12-15k mowers when brand new and intended for commercial use. I have inherited this one from my father two years ago. He used it commercially for over 10 years. It ran fine the last two years and last week it just wouldn't start. So here I am trying to diagnose it.