hey i am getting like 100 miles on half a tank and it's really bothering me, i think i have to change my head gasket but that shouldn't be killing mpg? what could be wrong do i have to make sure my engine is timed right and if so where or how would i do that? answers fast please it's really bothering me ( btw i drive a 98 gsr )

 

How warm does your car run? 1/2 way on the temp. gauge? Less?

 

Over the past few weeks until yesterday I was getting horrible gas mileage.My tire psi was good, oil was perfect. Sometime last week the cel light came on. I pulled the code and it was code 67(catalytic converter).I went and got a carsound univeral cat and replaced the stock one.Gas mileage was 10x better than before.Accelaration and throttle response also improved throughout the entire rev range. Hope you figure it out.