2006 WRX Wagon - bone stock.
I get phantom cylinder misfires - cylinders 1 and 3 are the most common. I've replaced the fuel pump with a Walbro 255lph unit, I replaced the fuel filter with a Subaru OEM new filter, I replaced the fuel strainers (both sides), I've tightened down all of the fuel line clamps (intake manifold was off) and used Gorilla Glue to try to negate the chances of the fuel line clamps coming loose. I have also replaced the fuel injector o-rings and run a few bottles of fuel system cleaner. I did replace the coil boot (not the pack itself, but the rubber stem that connects to the spark plug) with new Denso units. I've also replaced the spark plugs with Denso units - properly gapped (0.029).
My setup is simple:
Factory intake, factory TD04, factory intercooler, PTP turbo blanket, factory exhaust from the heads to the muffler.
The only modification that I've done (which actually helped) was adding an engine grounding kit (a la Paranoid Fabrications).
I have tried swapping the coil packs around, but the problem stays mainly at cylinders 1 and 3.
I've been debating either replacing the coil packs, but I am reluctant as if it does not resolve it - I've just dropped a lot of cash for nothing.
I've also been looking into changing the fuel delivery system from series (2, 4, 1, 3) to parrallel (1 and 2 then 3 and 4). I'm trying to find a way to relocate the factory fuel pressure regulator, but have had little success on that front.
So, I'm curious if anyone else has run a similarly (99% stock) setup and had similar issues. If yes, what resolved it? If no, any recommendations?