Thankyou to all who have contriduted on the above subject not that you solved my problem directly but i got ideas as to how to fix it.
My 97 outback EJ25 auto started using excess fuel about 1 year ago and slowly got worse to the point i was using 14liters per hundred Ks. (you convert) I could not find anything wrong and the problem remained after changing the motor after a blowen head gasket. I fixed or changed the following with minimal improvment. Injectors, Airflow sensor,PCV,O2,Fuel filter,Checked for blocked exhaust,air filter,fuel press regulator,plugs,leads, coil, and finaly the knock sensor and its now back to 10LPH or so. What i believe happened is the knock sensor slowly gained or lost resistance and could no longer detect Knock and so the ECM ran the engine at base timing in other words retarded the timing this meant i had to use more foot to get the slug to go thus more fuel.
So go forth all you fuel guslers and change the knock sensor and come celebrate with me in the great land down under. anyone for a BBQ and beer.