I know this sounds a bit stupid but why am I losing fuel economy? I drive very conservative, I recently purchased new spark plugs, cleaned up the air filter. It seems to me everytime I go to start the car the fuel gague moves a few ticks even though when I turned it off last it had more gas than it is showing. I have my tires properly inflated. If anyone could give me some tips or anything that could improve the economy or finding out what could possibly be affecting it that would be great. Thanks

 

Hope i don't get dinged for useless double post, but this is the exact same post i made last Friday:
You may have leaking fuel injector seals.
Put in new O2 sensors (read: Faulty Oxygen Sensor Fuel Economy | MpgEnhance.com ).
Put in fuel system cleaner.

 

Luca: I think Noggin has it perfectly right. The fuel pump puts the fuel rail under pressure and it stays under pressure unless the fuel injectors leak a little. When you start the car again the missing fuel is replaced.

In fact your question made me think this over, so thanks for asking!

 

Thanks a lot, ill check it out. A new o2 sensor would not hurt considering it has 178kms on her

 

Why? Is there a CEL on? If you change the pre-cat you should change the after cat HO2 sensor as well so they communicate at the same cadence with the ECU.

BTW, I made an error: there is a return line, so the fuel rail will not stay under pressure. But non-the-less the fuel injectors may be leaking and the easiest way is to treat the fuel system with an additive like Gum Out or Techron.
Also if the membrane in the fuel pressure regulator is broken then fuel goes into the vacuum line. You may check by taking out that vacuum line and smell for fuel. That's not good for your liver but you should survive if you don't make a habit of it.