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Discussion Starter · #1 ·
Hi Folks, I've been trying to get my John Deere STX 38 started. It has a Kohler 13 Command Engine and Hydro transmission. It turns over but won't start. There is no spark. I've checked out all of the circuits with a multi-meter, all fine. I have jumped the seat and brake pedal safety switches. I thought the iginition switch was the problem, replaced that today, still won't start. Now I have the engine cover off, there is continuity all the way from the ignition to the wire at the magneto. No voltage on this wire when the key is on. Ran the coninuity meter from the magneto lead to the spark plug wire, none. Do these magneto coils ever fail? What else could lead to no spark? Thanks for your input.
 

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Welcome to the forum Mark. Yes coils do fail and since it sounds like you checked things over pretty good I would say it is likely the problem. I'm guessing your engine is probably a CV-13. Here's the manual if you do not already have it from Kohler's website:

http://www.kohlerengines.com/onlinecatalog/pdf/tp_2339_d.pdf

Page 61 & 62 explains how the electronic ignition system works and troubleshooting procedure for the coil on that model. The electronics and the coil are combined together in one part. Makes the odds even better that is your problem. ;)
 

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Discussion Starter · #4 ·
Bad news, I replaced the magneto, and even the spark plug in case it was defective, and still no spark. At wits end here, what else could it be? Something grounding out the white wire to the magneto?
 

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Dang! :( It could still be a short on that kill wire someplace. You could try measuring resistance to chassis ground on it. If reads a short then work backwards from there. Maybe a wire rubbed bare someplace against the frame.

Have you removed the jumpers you placed on the safetys for testing? Depending on the configuration sometimes those switches or normally open rather then normally closed.
 

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Is there a nuetral switch on it ?
Did you also try removing all the safety switchs from the circut ? (running it hot)
Also check to see if the coil ground wire is shorted out to ground.
Just some thoughts that I would check first.
 

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Discussion Starter · #7 ·
Hi Mark and Bosmech, thanks for the reply. Sorry for the delayed response, I was away for the long weekend. I unplugged the junction wire to the regulator (that recharges the battery) and the white kill wire to the magneto, and presto, I had spark. I've plugged those back in and no spark again. So I think you are correct that it may be a short somewhere in the kill wire. I have checked and don't see any frayed wires grounding out anywhere. In terms of the safety switches, yes they are still jumped - one jumper in the seat switch, and 2 in the brake pedal switch. I'm not sure if any are supposed to be normal open, but I did have continuity from the white wire on the magneto all the way back to the ignition switch with the jumpers in place. I'll try your suggestion of working backwards checking resistance in the wire for a short, and the neutral safety. Need to figure this bugger out, as the grass is getting longer!
 

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Discussion Starter · #8 ·
Further update - unplugged the white jumper wire in the brake switch, and left the purple one in for the starter circuit. The good news is it now starts and runs, and moves; although brake and seat switches are currently bypassed. Bad news is when I turn on the PTO switch to engage the blades, the motor stalls out. Could that be a ground problem or low voltage?
 

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My guess would still be with one of the switches grounding, shorted, or open. I found a couple STX38 wiring diagrams on the net. You'll need to check your serial number to see which diagram applies.



 

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Discussion Starter · #10 ·
Hi thanks for the wiring diagram. Mine is the newer one (bottom diagram) with no neutral safety. I charged the battery and then checked the voltage to the PTO itself, she's getting 12 volts. With the key on and the engine not running, I pulled up the PTO and it clicks at the PTO which means the solonoid is engaging the PTO. I removed the belt on the PTO to the mower deck (to remove resistance and vibration), started the engine, pulled up the PTO switch, and the engine died just like turning off the key. So I think you are right, a short or ground out somewhere. In fact, the same short that was preventing the engine from starting before is most likely also causing the engine to stop when I engage the PTO. From the diagram it is probably somewhere in the black/white wiring, or maybe the PTO switch itself? The wiring goes into the frame so I cant see whether it is touching somewhere inside. I have a meter but not sure how to check it for shorts to ground - 0 ohms? How many ohms for normal?
 

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Switches working correctly would read infinity open and 0 ohms when closed. But if there is a short to the frame somewhere it could read anything from 0 ohms on up depending on how badly shorted it is. Short to paint could read higher resistance then a short to bare metal. ;)

But lets step back for a moment. This has to be one of those can't see the forest for all the darn trees problems. :D

I enlarged and sharpened the section of the diagram with the switches. If you have 942 White disconnected that ties into 941 White. With PTO ON, 941 then connects to 946 White/Black to the seat switch.

There appears to be an internal switch in the connector that plugs into the seat switch. So even if you have the seat switch connector jumpered, the internal switch in the connector itself might still be detecting it is unplugged.

At this point going back to the can't see the forest for the trees theory, I would remove all switch jumpers and reconnect plugs and wires like it all was originally.

I have the nagging feeling that you might have solved the original problem already by replacing the ignition switch or the ignition module but have inadvertently inserted a second problem while troubleshooting with the jumpers.

I've been there, done that. :eek:

 

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Discussion Starter · #12 ·
Hi Mark - once again you've been very helpful. You were right. I went back to the seat switch. I had ruled it out early on because the mower wouldn't start with the seat switch unplugged as well as jumpered closed, so I looked elsewhere. Turns out even when unplugged and not jumped, there is a spring inside the seat connector that you mentioned that grounds it out. This must be to prevent people from simply unpugging the seat switch to bypass it (it is a pain). So I tied a plastic wire tie around the springed plastic peice on the connector to keep it pushed in, and she started right up and the PTO works too. So the mower will work now! Only strange thing now is when I removed the wire tie and plugged it back in to the seat as it supposed to be, the mower starts with your foot on the brake, but then stalls when you take your foot off the brake (opposite of how brake is supposed to work). So I removed the connector again and tied it so I can run the mower. I'm thinking now that the seat switch itself is the problem..... Thanks again for your help! :)
 
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