Electricl Issues

[jack spratt]

I installed a new B&S on a Craftsman rider. Everything worked fine for about 3 hours and it died.Narrowed it down to bad mag. Replaced and worked fine for another few hours and same thing. The mag ohms at 4k, disconnected the kill wire from the switch and still no spark. Any suggestions? Thanks for your time. Engine is a 31P677 0236 G1

 

[Fish]

If all of this is true about your "mag", then you have low voltage being supplied to your "mag" via the "kill wire".

But I doubt it.... We need to explore the swap, and need all of the model numbers off of the engines [both] and the tractor as well.

 

[Rivets]

By saying bad mag, I'm assuming you mean CDI coil. Because of their design, you really can't rule them bad by taking a resistance reading, but need a specialized tester. Most shops do not use them, because they to will give false readings. If you have the coil air gap set correctly, remove the kill wire and get no spark, I would say you have a second bad coil. Only once have I seen a coil go bad in a couple hours, without a secondary cause. Did you have to change an wiring when you replaced the engine? If this was in the shop, I would install a new coil and run the engine with the voltage regulator disconnected. My thought is that you are getting some sort of back voltage going to the coil. You could leave the regulator connected and run the unit with the kill wire disconnected, but then you will need to figure a way to stop the engine. The only way to feed back to the coil is through the kill wire. I can think of one other possible cause, that is a bad key switch, which may be shorted. I must say this is not an electrical problem which I have seen before, so I am just guessing at this troubleshooting procedure.

 

[jack spratt]

If all of this is true about your "mag", then you have low voltage being supplied to your "mag" via the "kill wire".

But I doubt it.... We need to explore the swap, and need all of the model numbers off of the engines [both] and the tractor as well.

The mower is a 917.272650, the old motor was a 31C707 0230 E1 and I have disconnected the kill wire.

 

[jack spratt]

By saying bad mag, I'm assuming you mean CDI coil. Because of their design, you really can't rule them bad by taking a resistance reading, but need a specialized tester. Most shops do not use them, because they to will give false readings. If you have the coil air gap set correctly, remove the kill wire and get no spark, I would say you have a second bad coil. Only once have I seen a coil go bad in a couple hours, without a secondary cause. Did you have to change an wiring when you replaced the engine? If this was in the shop, I would install a new coil and run the engine with the voltage regulator disconnected. My thought is that you are getting some sort of back voltage going to the coil. You could leave the regulator connected and run the unit with the kill wire disconnected, but then you will need to figure a way to stop the engine. The only way to feed back to the coil is through the kill wire. I can think of one other possible cause, that is a bad key switch, which may be shorted. I must say this is not an electrical problem which I have seen before, so I am just guessing at this troubleshooting procedure.

All the wiring was identical. I have disconnected the kill wire to the coil. I can put a toggle in to take care of the kill, but everything I have read says the coil ohms out correctly.

 

[Rivets]

The coil has two circuits, a primary and secondary. If you put your meter across the plug wire and ground, you are reading secondary only. In my experience a secondary reading should be in the 15K range. I know of no way to measure the primary circuit, with out a dedicated tester.

 

[ILENGINE]

I would bet you are getting a volt feedback through the kill wire to the ignition module, or a voltage spike from a voltage regulator, or electric clutch when turned off. Could be also caused by a bad ground that is causing a voltage leak looking for a ground.

One bad module could be a fluke, a second one failing with a couple hours of the first, I would be finding out what is killing the modules.

Like Rivets said, Key switches are the most common cause of toasted modules, but have also seen electric clutches or even bad batteries, coupled with a voltage spike kill modules.

 

[Fish]

Yes, if a full 12 volts goes to the coil, it will destroy it almost instantly, if you are getting partial voltage bleeding into it, it can take some time before it destroys it.

So before trying another good coil, take dc voltage readings at the kill wire, with the keyswitch turned to every position, jiggled, jiggling wiring, etc.

Also look for frayed, pinched, or molten wires, especially near the exhaust and steering, but everywhere/anywhere.


But basically, with the kill wire disconnected, and a good plug on the plugwire, side of which is grounded against the block, when the engine is cranked, you should
have spark, if you don't the coil is bad. You may have killed your new coil as well, so you want to find out where the voltage is coming from.

 

[jack spratt]

Yes, if a full 12 volts goes to the coil, it will destroy it almost instantly, if you are getting partial voltage bleeding into it, it can take some time before it destroys it.

So before trying another good coil, take dc voltage readings at the kill wire, with the keyswitch turned to every position, jiggled, jiggling wiring, etc.

Also look for frayed, pinched, or molten wires, especially near the exhaust and steering, but everywhere/anywhere.


But basically, with the kill wire disconnected, and a good plug on the plugwire, side of which is grounded against the block, when the engine is cranked, you should
have spark, if you don't the coil is bad. You may have killed your new coil as well, so you want to find out where the voltage is coming from.

Found internal short in keyswitch, took apart and cleaned, put it back together, after finding the spring I lost in a groove on the bottom of my shoe, three days later.


getting ready to try it.