I have been fussing with a Deere 318 tractor for a number of weeks now. The engine is good(compressions comparable

Hello,Customer

I believe I can save you a lot of trouble here.

You do not need to tear the engine down to get at the ignition controls.

I can assure you that the ignition module and trigger ring (the circular thing), are working properly. If they weren't, you would be getting no spark to either plug.

The way this ignition system works is this:

The coil has 2 windings in it - the primary and the secondary. The primary winding is the winding with the 2 small posts (positive and negative). The secondary winding is the winding that the spark plug wires attach to.

Battery voltage is fed to the coil's positive post, and then to the ignition module, through the red wire (in your photo, it looks like yours has faded to orange).

The ignition module is a set of magnetically operated contacts, which open and close like a set of points.

The trigger ring, which is mounted under the flywheel (not inside the gearbox), snaps on to the crankshaft. It has 2 magnets inside it (positive and negative), mounted 180 degrees apart.

As the trigger ring spins, one magnet opens the contacts in the ignition module, and the other magnet closes the contacts.

When the contacts are closed, the 12V is fed back to the negative terminal of the coil through the black wire on the ignition module, and on to ground.

When the voltage is ran through the primary winding of the coil, it creates a very strong magnetic field inside the coil. This magnetic field goes around the secondary winding. As the magnetic field collapses when the IM contacts are opened, it creates a strong surge of power in the secondary winding. This process is called induction.

When the current moves in the secondary winding, it is sent to the spark plugs.

Both plugs are connected inside the coil, so both plugs fire at the same time, twice every revolution - once on the compression stroke, and once on the exhaust stroke.

If you are having spark on one plug, there are only 3 causes for the other plug to not have spark:

1. A bad spark plug.

2. A bad coil.

3. A bad spark plug wire.

The coil is very easy to test with an ohmmeter.

Remove all wires from the coil.

Set your meter to ohms, and connect the leads across the primary winding (the small posts). It should read 2.9 - 3.6 ohms.

Now connect the leads across the secondary winding (the spark plug wire terminals). It should read 14,500 - 19,800 ohms.

When reconnecting the coil, the black wire from the ignition module will go to the negative terminal, and the positive terminal will take the red wire from the ignition module, the capacitor wire, and the 12V supply wire.