Perhaps, try to inspect your spark plugs and wires.
I would recommend that you start by addressing code P0304, since code P0304 might be spark-plug related, and spark plugs need to be replaced on occasion anyway. Take the rubber boots off the spark plugs by twisting and pulling on the boots. Start with cylinder 4, since that is to where the code is pointing. Cylinder 4 is the cylinder which is the farthest from the timing belt. The wires leading to the spark plugs should be labeled with each cylinder's number.
Once you have the spark plugs out, inspect them. Measure the gap to make sure that it is within specification. The gap on my spark plugs were too big, so I replaced all of mine. I replaced them with the spark plugs designated in the owner's manual. I bought mine at Advance Auto Parts, and to purchase all four of them, I paid less than a total of $8.
After you have done this (and driven around at least three times), go back to AutoZone, and have the codes read again to see if the misfire code is gone. If it is not gone, you either need to drive more or maybe replace the spark plug wires and ignition coils.
Let's now address the other code. According to the 1998 Hyundai Accent Shop Manual, P0455 is described as "Evaporative emission control system incorrect purge flow." The component your mechanic should check is the evaporative emission control system. If the evaporative emission control system is malfunctioning, this might be the reason why you are having a difficult time filling the gasoline tank.
Once you have done all of this, come back and post your results! This forum works the best when we share our results with everyone so we can build a knowledge-base for people in the future with the same problems.
Once you have done all of this, come back and post your results! This forum works the best when we share our results with everyone so we can build a knowledge-base for people in the future with the same problems.
Folks get good to smart to brilliant to wise assistance here, for the most part, but too many times the simple courtesy of reporting back the findings, results, fixes, and conclusion(s) goes unextended.
Probably an intake leak or a leak in the evap system. Since its a vacuum system, it will suck in air leaning out the mixture. Cylinder 4 is closest to the inlet for the evap into the intake manifold so it's more likely to misfire.
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