Noticed that my long term fuel trims have dropped negative over the years and am wondering if something is up with the positive crankcase ventilation system.
I am familiar with logging data so logged a couple hours with the breather hose connected (the first pair of trims) and then disconnected (second pair) and ran the results into a spreadsheet. Each time I allowed the engine to get to temperature and had separate drives to relearn between runs.
Looking at this I am wondering why the trims are higher, e.g. more positive with the breather hose disconnected. Obviously in that scenario I'm allowing unmetered air to the intake manifold but shouldn't there be just as much air coming with the breather hose connected?
This table is from a 2008 Subaru 3.0 showing just bank 2 as both sides have similar results. The PCV valve is replaced recently, the hoses are in good condition with genuine parts used.
|MAF g/s||Min LTFT||Max LTFT||Min LTFT||Max LTFT|