Electrical Issue? I’m out of ideas....

[AimmeAshley]

Okay, I finally got a hold of jumpers.

I bypassed the PTO and brake switch by shorting both the purple and purple/white wires on each one.

I also bypassed the seat switch by placing a piece of business card between the tiny slot on pins 2 and 3.

I removed the starter motor and checked the kill wire to see if it was shorted to the engine chassis, and it wasn’t. I ended up placing electrical tape around the wire anyway and the starting motor back in place.

With all the bypass jumpers in place, and with the kill wire connected back to the ignition coil, I’m still not getting a spark.

Then, I removed the hour meter/service reminder. Behind the hour meter device are 4 tabs. With the hour meter removed, I measured the resistance from the ground tab (where the black wire would normally go) of the hour meter to where the tab where the white wire would normally be connected. This white wire would normally goback to the magneto on my D100 schematic. This gave me the 9.89KOhms that I normally saw from my kill wire to ground that I saw originally.

If the kill wire to ground is normally supposed to give me an open load with the ignition switch in the run position, then my gut feeling is the hour meter is internally shorted.

With the kill wire removed and the hour meter unplugged, the mower wouldn’t start. I guess the mower requires the hour meter to be plugged in be able to provide spark. Once I plugged it back in, with the Kill wire still removed from the ignition coil, the mower would start.

Looks like there’s an internal short from hour meter? Is there a way I can test out the hour meter, aside from my resistance checks?

If anyone has a similar mower, would someone be willing to remove the their hour meter and give me a resistance measurement from where it would normally connect from ground to magneto?

 

[bertsmobile1]

If the hourmeter is also the safety switch interlock then yes they do go bad.
Back test wires with the meter in place to ground.
If the white wire shows ANY ground connection then the hour meter is kaput .

 

[Telesis]

A couple things just to note. Your magneto is spec'd to output 12 VAC on the kill tab. The hour meter uses this to know if the engine is running or not(the white wire going to the hour meter #405). The hour meter does not increment with just the key on and 12 VDC present. The engine must be running. The kill tab behaves like any other in that when it's shorted to ground, spark is inhibited.

I have a D105 which electrically is essentially identical to yours. I disconnected the kill wire at the magneto and measured infinite resistance with the key in the run or run with lights, engine running or not. I measured 6.2 VAC from my magneto, engine running WOT, kill wire connected to rest of wiring or open circuit. Hour meter draws about 115 uA of AC current while running. I also wanted to know how much or little resistance the kill circuit would take to stop the running engine. In my case anything less than 27 ohms kills a running engine. Anything above does not. (I tried 9.89K ohm first. Didn't kill it!)

To test whether it's the hour meter causing your problem, disconnect it. You'll need to jumper the yellow wire(switched 12 VDC #401 on schematic) to the yellow/white wire(#407) which feeds the fuel solenoid and the RIO latch relay. When you did your test with it disconnected(no jumper) did you check for spark? If not, it probably didn't start because the fuel solenoid was not powered.

Finally, Bert, if you measure the resistance to ground from the white wire at the hour meter(or any other place in the kill circuit for that matter), you would be doing EXACTLY WHAT YOU SQUAWKED ABOUT EARLIER. The white wire goes to the magneto kill tab and unless you disconnect it at the mag, it will show 1.6 ohms, the primary resistance and you'd effectively be placing your ohmmeter between the kill tab and ground. Remember those microchips in there..... I for one am not too worried about damaging this magneto by measuring its resistance from kill tab to ground since it puts out 12 VAC on that same kill tab. Not to say others could be damaged. Comments apply to this one.

 

[AimmeAshley]

A couple things just to note. Your magneto is spec'd to output 12 VAC on the kill tab. The hour meter uses this to know if the engine is running or not(the white wire going to the hour meter #405). The hour meter does not increment with just the key on and 12 VDC present. The engine must be running. The kill tab behaves like any other in that when it's shorted to ground, spark is inhibited.

I have a D105 which electrically is essentially identical to yours. I disconnected the kill wire at the magneto and measured infinite resistance with the key in the run or run with lights, engine running or not. I measured 6.2 VAC from my magneto, engine running WOT, kill wire connected to rest of wiring or open circuit. Hour meter draws about 115 uA of AC current while running. I also wanted to know how much or little resistance the kill circuit would take to stop the running engine. In my case anything less than 27 ohms kills a running engine. Anything above does not. (I tried 9.89K ohm first. Didn't kill it!)

To test whether it's the hour meter causing your problem, disconnect it. You'll need to jumper the yellow wire(switched 12 VDC #401 on schematic) to the yellow/white wire(#407) which feeds the fuel solenoid and the RIO latch relay. When you did your test with it disconnected(no jumper) did you check for spark? If not, it probably didn't start because the fuel solenoid was not powered.

Finally, Bert, if you measure the resistance to ground from the white wire at the hour meter(or any other place in the kill circuit for that matter), you would be doing EXACTLY WHAT YOU SQUAWKED ABOUT EARLIER. The white wire goes to the magneto kill tab and unless you disconnect it at the mag, it will show 1.6 ohms, the primary resistance and you'd effectively be placing your ohmmeter between the kill tab and ground. Remember those microchips in there..... I for one am not too worried about damaging this magneto by measuring its resistance from kill tab to ground since it puts out 12 VAC on that same kill tab. Not to say others could be damaged. Comments apply to this one.

Okay, with the hour meter disconnected, I also connected the kill wire back to the ignition coil, and then jumpered the yellow and yellow/white together and then....IT STARTED!

You were right, I wasn’t getting +12V previously to the fuel solenoid after removing the hour meter.

Now I need to decide whether it’s worth buying the silly hour meter or just leaving the jumper in place.

Thanks so much for your suggestion and help!

 

[Telesis]

Terrific news! I'm fairly certain JD runs that power thru the hour meter as a cheap and dirty way to keep the average person from just unplugging it to 'save time'. Their warranty is based on both years and engine hours so if someone just unplugs it to save on the hours, it won't start because of the fuel solenoid! FWIW!

 

[mitchstein443]

What you just experienced is "engineered to fail". Almost every manufacturer is doing it, they design one part that is integral to make the device work fail so that the average consumer will throw it away and just buy a whole new device. I just went through that with a GE dishwasher. at almost exactly 3 years old the solenoid that controls circulate or drain valve selector failed. Upon removing it, it is clearly stamped on the solenoid .5 minutes on 10 minutes off for the duty cycle and they (GE) have it run for 3 minutes nonstop. so of course it always overheats and eventually becomes the fail point. Then they charge 89$ for the part and 125$ for a tech to ocme out and put it in (they claim it is not a consumer replaceable part). So ebay had the part for 18$... put it in, running like a champ... The washer cost 336$ brand new at homedepot or lowes...

 

[matt man]

On these engines, every time the flywheel turns, it produces a spark, the 12 volt system is out of the loop, and if 12 volts is introduced to this tab, it will destroy the coil. So if the engine runs fine without the coil hooked up, then your coil is fine, and your trouble is somewhere else.
When the coil is grounded by the switch/system, then the engine shuts off.

Hi,

Yes, I checked the ignition switch by fully unplugging it. I checked all positions. Without anything attached to it and at the Run position, M and G are open.

The model number of the D100 is:

1GXD100ELBB138416

Btw, is the kill wire tab at the ignition coil normally supposed to grounded to the engine chassis?

Always check the spark plug too. I kicked myself a time or two, for not