As D-Rig pointed out, does the Check Engine light come on when turning your ignition to 'on' before cranking the motor? If it doesn't, they strictly disabled the light, and more than likely never touched your #4 plug. (which is why it is now blowing out a year later and not showing a check engine light.) If a blown plug does not give you a check engine light I'm not sure what would! (At that point you would have a 'miss' to say the least.) As you've probably found out by now, this is not a cheap repair, so I'd definately see if you can determine if whoever swapped your plugs is responsible.
Last edited by STX/98; 12-22-2003 at 05:44 PM.