p0301 & p0420

Hell all, I have 98 accord lx 4cyl 138000miles. recently did a tune up 1 month ago when "CEL" came on. light went off in 1 day. recently light has returned with the following codes p0301 & p0420. have done some research and im just lost. could one be causing the other to happen, or should i just change the plugs with a different brand, and change both o2 sensors. i have to get my emissions in two weeks, please help. I used bosch platinum plugs, i forgot what brand of wires but they werent cheap. thanks

P0301 indicates that the your car has misfired in cylinder bank one. Misfires, over time can damage your catalytic converter and cause a code like P0420 which indicates that the catalytic converter is operating below efficiency. A sulfur smell coming out of the exhaust usually follows these simptoms.

Not exactly sure how the 98 engine is laid out but three components get the sparks going inside the cylinders: the plugs, the wires, and the distributor. Since the plugs and wires are new, I would make sure that the wires are properly connected on both ends and that all internal contacts are clean. Applying diectric grease at these connection points wouldn't hurt and will help prevent corrosion build up. If the distributor is electric (not hooked up to one of the rotating shafts of the engine), I would inspect the housing for cracks which could be letting water get inside and cause the misfires. Regardless of whether the distributor is electrical or mechanical, it might be the culprit vice the 02 sensors which are sensing uncombusted gasoline. If the problem persists after these checks, it is time to start looking at the 02 sensors and catalytic converter as you said. Warning, OEM catalytic converters are not cheap.

Bosch plats suck. I've pulled more of those out of motors due to problems caused by them...misfire codes, jittery idle, etc

Always use Denso or NGK plats in a honda.