My Subaru wrx spark plugs foul and miss fire and no one can figure out why. It has added turbo and fuel injector

OK- a 2003 WRX has no doubt been driven HARD- for 10 years- if anyone is gonna buy a 10-yr-old- hot rod, they should be ready to rebuild the engine, just as normal procedure- in your case, it sounds like the engine is worn, that's why the plugs are fouling, worn rings, or valve guides, or burnt valves, or bad head gasket- whatever it is, it will be cured with a COMPLETE rebuild- and the guys whose shop you have it at- sounds like they're sleeping or stoned or somethin'- and if this engine is modified- what a mess- why buy something like that in the first place?

I've owned the car for 5 plus years car has a little over 100,00 miles. mods were just done and ran fine before. It also runs fine with new plugs the just foul after its been driven awhile.

ok- the added info is helpful- first, it would seem to me that whoever did the mods should be responsible for getting it to run right- why start wrenchin' if ya don't know what yer doin'- having said that, are the plugs fouling white, black, wet, or dry? if they are wet, that's oil, and my previous answer would apply- if they are dry, black- it would be fouling with gas, running rich, and there may be an easy fix to that, short of rebuilding the engine (and returning it to stock)- at the very least, after "months" of head scratchin' I would go get my car and demand my money back

What sort of injectors are added? It sounds at this point like it's fuel related, and the tune and injector scaling is off.

plugs are black so I believe its fuel. tried almost everything fuel related but throw some idea at me anything really small and stupid it could be!

If you have a boost leak, that will cause you to run rich and foul plugs.