I performed a compression test today on the engine and found 140 for cylinders 1 and 4, and 155 for cylinders 2 and 3. This does not look too good, but should that be enough to cause a low power and poor gas mileage (15.3 mpg on highway). I added a little oil for 1 and 4 cylinder and test again, both compression went up to 150. I know this is not good but how bad is it?