Check engine light

[abaum565]

A couple of weeks ago i was having trouble with my car studdering while accelerating. It turns out it was fouled plugs. So i replaced the plugs and wires and it ran great.

At the same time i installed the apexi N1 turbo back system (no cat). and an air intake. Everything ran great, no studdering or anything.

yesterday i was driving on the hwy and my check engine light came on. so i went to autozone to get the code checked and it came up as this:
1-P0304: Cylinder #4 Misfire
2-p0420: Catalyst Effiecncy below threshold (bank 1)

do you think i should change the plugs and wires again?
and is this probably a bad rear o2 sensor?

Anyone else have this problem in the beginning stages of upgrading?

Thanks guys

 

[ryno]

First off check your plug gap and make sure its fine. Also make sure your wire is still good on cylinder number 4. Visually chack it for any arching holes. Have you gotten any water in your engine bay lately? Maybe washed it off? If those all pass, then you could start by doing new plugs and wires, just make sure you gap it right, if the gap is way off it will have a tendancy to misfire. And the rear o2 sensor isnt bad, its just reading you have way to much carbon/exhaust coming thorugh, due to no cat. You can just unplug the o2 or do the o2 eliminator mod which can be found on www.vfaq.com.

 

[abaum565]

I didn't get any water in my engine bay lately, but it did rain hard and it sat overnight. Will that make a difference? thanks

 

[ryno]

If water got down in you plug holes it could cause arching from wire to the wall. So i would start off by getting new plugs and wires, and deffinetly make sure you gap the plugs right!

 

[olmytsi]

These cars are not new, the same shit has been discussed over and over:

http://dsmtuners.com/forums/search.php?searchid=2112688

http://dsmtuners.com/forums/search.php?searchid=2112692