could be a few things: battery on your ez start could be low enough to turn over the motor but not heat the plug. glow plug could be bad. yellow ground wire might not have a good ground contact. blue wire could also be bad at the tip, or have a bad connection. i still use my ez start, but i ditched the blue/yellow wires and went with a glow plug Igniter. works so much better, and my ez start battery lasts twice as long, as it's only drawing power to turn the motor. it took me awhile to convince myself go that route, but once you do you will solve all your problems !