exhaust leak

l have a 95 F150 with a 302 cid it only gets about 13 mpg would an exhaust leak at the manifold cause it to get such lousy mileage l've changed the plugs air filter an EGR valve l'm not getting any codes but i'm not getting any gas mileage eather .

If you have a whole you are not typically going to get less mileage. You should change the PCV. A lot of the time a tune up can give you higher emissions, because the air mixture goes up. Did you gap the plugs? This is important for tempature of spark, and the converter. You could be reburning more gas than it should be from the tune up. Also if you did the tune up you should use low to middle grade fuel. This will help with mileage.