Have to replace ignitor on coleman furnace every...

Question

furnace runs fine then stops; diagnostic lite blinks once to indicate ignition failure; ignitor shows black burn marks; replace ignitor and unit will work for the cold season then burn out next year; has done this for six seasons; it is a coleman for manufactured hones 70.000 btu. I put voltage meter on it and it read 122 volts; is this too high and could this be burning out ignitor?