For a long while now my sf forester has a rather annoying feeling of lack of power or a miss fire, it boosts to correct pressure everytime but some days you can feel it boosting, other days it's just rather subtle more like a n/a, done the usual checks and I'm thinking fuel pump not keeping up some times, but also when I fill up there's a lot of air hiss when I remove the cap, so I'm wondering if it sounds like it could be related? Ie tank not breathing properly and not allowing enough fuel to engine, I've looked but can't figure out how it breathes cos of the stupid evap canister, can this be removed or does anyone know how to check it? 

 

Many thanks, Ben 

The hiss is usual, wouldn't worry about it it's either a weak pump or the maf or 02 sensors are a bit duff and trimming the air fuel mix or could be something pulling the timing, have you done the ecu self diagnostic ? May have flashed up a cel without noticing

 

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