John Deere Riding Mower No Spark

Spark Test Procedure

1. Remove and inspect plug — Pull the spark plug. Look at the electrode: black and sooty = running rich or oil fouled. White or light grey = normal to lean. Wet with fuel = flooded. Replace the plug regardless — they cost $5 and are always part of the diagnosis.
2. Test for spark — Reconnect the plug wire to the new plug. Hold the plug base against bare metal on the engine block (not the plug hole). Crank the engine. You should see a strong blue-white spark. Weak yellow or no spark = coil problem.
3. Test kill wire — The kill circuit grounds the ignition coil to stop the engine. If this wire is shorted to ground (chafed wire, stuck kill switch), the coil is permanently grounded and produces no spark. Disconnect the kill wire from the coil and test for spark. Spark with kill wire disconnected = kill wire or switch is the problem, not the coil.
4. Ignition coil gap — The coil sits close to the flywheel magnets. The air gap must be set correctly (typically 0.010"). If the gap is too wide, spark is weak. Use a business card or feeler gauge to set the gap with the coil bolts loosened — the flywheel magnet will pull the coil to the correct distance.
5. Replace coil — If spark is absent or weak after a new plug and correct gap, replace the coil. John Deere coils run $20–55 and are straightforward to swap.

Parts & Costs

Part	Cost	Notes
Spark plug	$4–10	Always replace first. Cheap and often the fix.
Ignition coil	$20–55	No spark after plug = coil. Set 0.010" gap on install.