If we’re going to have a discussion about fuel mileage, I think we need to work the fuel system into the conversation. Fuel-injected engines need a given fuel pressure to run properly. If that fuel pressure isn’t correct, it will affect the overall operation of the engine and the MPG. So if you suspect a problem with your fuel system, a good start is a fuel pressure test.
If your fuel pressure isn’t correct, don’t condemn the fuel pump just yet. It’s also a good idea to check the operation of the fuel pressure regulator and the fuel filter if equipped. A clogged fuel filter can cause a loss of fuel pressure. A faulty fuel pressure regulator can not only mess up the fuel pressure, but it can also leak. If you have a leaking fuel pressure regulator, you will have poor MPG. There’s a lot more to this testing, and I cover it in more detail in the Solving Automotive Performance Issues article.