At the same time i had the smell before i even started modding the car.

 

no... but your o2 sensor not plugged in could be WHY your CEL isn't on... You're O2 is telling your engine what your car is letting out... So I'd maybe plug that in... >.<

 

Actually you don't need the 2nd o2 plugged in, you'll just get a CEL.

But please get a cat converter, save your lungs as you drive and the environment.

 

Hydrogen sulfide in the exhaust, which is produced by trace amounts of sulfur in gasoline. It's supposed to be converted to sulfur dioxide in your catalytic converter. This may be indicative of a fuel-injection problem, and can be cured by a sharp mechanic. But often it means a failed catalytic converter.

This also happens after a new exhaust and or headers are installed, but it normally goes away after a day or so. it could also be related to a different gas mixture (different gas station) and or fuel additives.