I know the LTFT on my 10 year old engine is +7 and +4.5 at the moment even though I have no vacuum leaks.

I'm told that these numbers tend to go up with time as the engine wears out, gets dirty, becomes less efficient etc.

I wonder if anyone knows what the LTFT values were for these engines back when they were clean and new?

 

The absolute ideal LTFTcondition is 0%. I can't really say whether a brand new engine would show an ltft of 0.

+ readings on ltft indicate an ECM correction for a lean condition and set an over fuel injector pattern. The ECM in closed loop relies on input from O2 sensors to maintain a stoichiometric air fuel ratio that the cats need.

O2 sensors wear like spark plugs and can start to stretch the signal for which the ECM is looking, so it doesn't have to necessarily point to vacuum leaks. MAFS signal variants through wear can change the ltft too. Exhaust manifold leaks can cause a + ltft, although not much of a known problem on the AJV8, a far bigger problem on the AJ16 which was well known for cracked exhaust manifolds.

Once LTFT dirfts higher the thre most common targets are - MAFS, Fuel injectors, O2 Sensors.