John Deere D100 - No Spark
 

My friend has a D-100 two cylinder (likely a Home Depot model) that died after it was parked.

No spark from either plug. I cannot find a schematic online.

It has twin coils with diodes that go to ground (I think), I would expect this to be grounded to kill the engine?

No manufacturers name on the engine. Might be Briggs and Stratton?

A schematic would point me in the right direction to figure out why both coils have failed.

Anybody have any suggestions?

Pull the kill wires off each of the coils(at the coil) and see if it sparks.

Pulled one off, broke it and stopped. Still no spark from the one I took off...

Pull both off. How are you checking spark?

Also, some have a low oil sensor that won't allow spark if the oil is low, but pulling the diode wires eliminates that.
Post a pic of the motor so we know what you're dealing with.

I'm just grounding the plug to the case. No blue spark.

I will get a picture if it doesn't start.

Since I unplugged the one coil I should have got a spark there...

Yep, if you unplug the kill wire from either coil, that coil should spark. Have you tried new plugs?

I have not tried new plugs, but since they both died at the same time it has to be something else...but all I can think is the flywheel magnet died...what else is there in common?

I have seen both plugs fail to fire at the same time.
The only way for the flywheel magnet to fail is if it let loose from the flywheel.
I'm assuming this is electric start. Make sure there is a good ground between the engine block and the battery.

Riding mowers have numerous "cutout" switches that will kill spark....Seat, blade engage, reverse, etc.

Run a jumper wire straight from your battery positive to where your engine gets it voltage.

+1 For the oil pressure cut off switch.

LOL on the other cutoff switch(es). I remember buying my JD and trying to unload it from the delivery truck. Every time I got off the seat to see why it kept cutting off, it would- CUT OFF!!!!!

THE FIRST THING TO GET BYPASSED WAS THE SEAT CUTOFF!!!!!

If you remove the kill wires from the coils, it eliminates all of that crap.

I am thinking two things: poor ground on the plug when I tested them and low oil.

I will report back, thanks for the suggestions.

I like the suggested idea of disconnecting the ground line from the magnetos.
That confirms they are good, and something else is shorting it. Then it's just a matter of confirming what is shorting it.

As for the oil pressure cutoff... perhaps low oil.
I would think the oil if ok, but switch itself is frozen shut from disuse.
Also, longshot- oil pump intake/line itself is clogged from disuse,

Interesting stuff, these little engines.
Also? was ignition switch changed at any point. Wrong type reinstalled could spell trouble. They look the same from outside, but there is a huge difference between the coils and magneto type switch internals.(another longshot)

updates please!

Again, disconnecting the kill wires from the coils will eliminate everything ahead of it.
I have a 16hp Briggs twin making close to 50hp. This is my favorite motor, so I know a little about it.

50hp?? Please tells more / possibly new thread.....

40 shot of nitrous...

I've been sent to sunny California for work.

I doubt I can update this thread before next week.

I just finished rewiring our JD mower last night. There are no more safety switches, you turn the key, it starts.

Previously, there were safety switched for the pto, seat, clutch, etc... The connections are corroded and I was tired of screwing with it constantly...

The wire going to the coils should never have positive voltage hooked up to it, it will melt down... You ground this out to kill the spark - my notes in the top left are incorrect in this regard...

http://forums.pelicanparts.com/uploa...1467334097.jpg

This is what happens if you hook up 12v to the coil...

http://forums.pelicanparts.com/uploa...1467334243.jpg

Also, arns equipment is cheaper and better to deal with than EJ Mower and can get you aftermarket parts.

He pulled the ground from both coils over the weekend, now the starter won't engage...

I need to go have another look when I get home.

Curiouser and curiouser.

I think I will pull the coil grounds and hot-wire the starter solenoid when I go back there.

Just to be clear...

The wire going to the coil is not the coil ground. The coils are grounded to the engine casing, which is grounded to the battery.

The wire going to the "Magnetron" coil is for the ignition kill circuit. Grounding that wire will kill the coil, and shut down the engine.

This is what I was referring to....

http://forums.pelicanparts.com/uploa...1467668993.jpg

There is only one connection on each coil, it's a ground wire (I think) that kills the spark. There are two (since it's a two cylinder) and the ground from each has been removed.

Still no spark with the wires removed? They must be removed at the coil, not the other end. There is a diode in each wire, so it must be removed from the coil end.
The motor needs to spin at least 250-275rpm to be able to achieve spark.
Did you try new plugs?

I think I have it wrong.

I believe the body of the ignition coil is grounded, the wire with the diode in this picture needs 12V (X8).

I am 90% sure we did not have 12V on the coils, which from the drawing page 2 (not shown) is likely a starter switch issue.

http://forums.pelicanparts.com/uploa...1467675887.jpg

If you apply 12v to X8 you will fry the diodes and possibly the coils.

Unplug the diode wire from both coils.
Turn the engine over and check for spark.

You said the starter wouldn't turn over. That could be a bad ground to the engine block, which would also cause the no-spark. It should be a large cable going from the battery negative, directly to a block mounting bolt. Yours may go to the frame, then to the block.

I build these engines all the time. I have 10 of them in my shop right now.
Again, it could be the plugs. One plug could have been bad for a long time, and the other one decided to crap out now. Most people can't even tell when this motor is hitting on only one cylinder. It will be low on power, but still sound almost the same.

Like I said, I just went through this last week.

The wires that go to the coils are to ground out the coil to shut off the engine.

The positive wire that goes to the magneto goes through the switch to the battery and must be grounded out when the engine is shut off to discharge the mag. There is a diode in this line which makes it pulsed DC.

The other wire goes to the head lights.

You may have a carb solenoid. This needs to have power when the engine is running / starting or it won't start.

Got it...will report back.

Red 88 was closest. Two bad coils. Per his suggestion I suspect it was running on one cylinder and then the second coil crapped out.

Replaced both coils and it fired right up.

Thanks for the help.