Friday night my Blazer wouldn't start . So when I was cranking I was getting smoke so I know I have fuel . So then I checked my glowplug wiring and juice was going to those . So I figure my Glow plugs are bad . Been hard starting for about a month or so . So I pulled a glow plug and hooked it up to a 40 amp charger and no heat ? Is there another way to check them or is that a good way ?