Camshaft position sensor

Hello, my car is expending a lot of gas sometimes I have seen some smoke when I try to go fast (to pass someone), first it was hard to turn it on but the mechanic told it was the gas pump he changed and now starting fast but still using a lot of gas, I have read that the problem is the camshaft sensor but I try to find and I looks like it doesn’t have.
By the way he used the scanner and it says is the oxygen sensor but I already changed (about) one year ago.