i curently have bosh 4 plugs in my car, they where allright for a while but after 30,000 miles they give me problems starting and when i take them out and look at them they are always black so i clean them off and put them back in. should i put new ones in? and what should i put in? has anyone tried the pulsar plug for a focus or do the burn to hot? ive looked in to ar104 but no one has them here in southwest fl.