well since you have a 4 cylinder and you have "headers", you should take one off since a 4 cyl only has one "header". anyways... check the gasket. Also the flex pipe on that design sucks terribly, and if its an ebay header, they probably used the cheapest shittiest flex pipe possible. Look and see if it has black sooty carbon on the outside of the flex pipe. if so, thats probably the problem.