Head gasket, lower intake gasket, Or worst case scenario a craked head or lower intake manifold. My mechanic told me the 98-00 4.0 head gaskets and manifold gaskets fail easily especially if the motor ever overheated. One tell tell sign that this is a problem is if you have to keep refilling your radiator fluid. Itll be a slow leak so check it every couple of days......If this is the problem its cheaper to have the gasket replaced than to get a quote of 2500-3200 to get a rebuilt motor put in. When I had this problem I gave it a tune up and replaced the coil and threw all kinds of money at it. I only started getting codes towards the end of the motors life, codes like cylinder missfire over and over, emmisions control unresponsive ( wich was funny because Mine didnt have an egr), system too lean. As I just filled it with water and replaced plugs the #1 started to go. Dont mean to scare you but I would fork the cash to have it professionaly checked by a shop who is used to working with these motors.
What do your plugs look like after they burn up. The condition of the plugs will give you a pretty good idea of whats going on. The only thing that could be wrong with the coil pack itself is that its arcing in cy 4 sending too high of a charge to the cy 4 plug wich I would think would be unlikely, generally speaking (but not 100% true) the coil pack works or it doesnt theres no inbetween. If the pack is causing problems but its still working then you would have an electrical issue somewhere else
Have you checked for vacuum leaks, fuel pressure, sometimes you will get a random or cylinder specific misfire from poor or low fuel pressure along with a vacuum leak check the large vacuum hose that comes off the passenger side just behind and below the throttle body. You have to move the top radiator hose to be able to see it.
no i have not.. Unfort. i am headed on a 10 day TDY tomorrow so i cannot do anything with it, so while its in the shop to finish the BL, im gunna have him check the engine out.. Hopefully he can figure it out/.