P0304 wont go away can it be a Cat?

[Froggy Ford]

Hey guys, so heres what the stink (98 expy 4x4, 108k, flow master exhaust, k&n cai sys) driving the other day and noticed a miss and running rough and when it got to overdrive it falls on its face like im running on 3 cyl's...check code/s only coming up with p0304 so i replace coil pack start it up clear the code and it idles nice and how it used to. Take out for about a mile and pulls same crap but now ce light comes on and flashes with same end result of before as far as how its running and also smelling faint rotten egg smell (cats) any suggestions of what to replace next? O2 sensor, plugs, or just do cat delete?

 

[Jason_CPAPS]

Assuming you replaced plug when you did the CoP?

 

[FordandPolaris]

Assuming you replaced plug when you did the CoP?

+2 on that question. Check your fuel injector as well just to rule out the items on top of the cylinder.

 

[Froggy Ford]

As a matter of fact guys no i didnt, previous owner stated he had done plugs a few thousand miles ago..also while looking around i noticed that all of the 8mm hold down screws are not installed on any of the 8 cop/s..so dont know if that could be suspect or if i would throw more 300 codes..so guess i cautiously remove that #4 plug and see whats up, wouldnt surprise me if all plugs but 4 and 8 were replaced since there a bear to.get to..thanks for chiming in guys..