Gas Problem!

[hellllo]

I've searched trying to find each symptom my car has relating to my gas problem, and haven't found answers.

Problem: I dont think its normal for SRs, but my car uses about 3 gallons of gas per 50-60 km's (about 10-12mpg). Its my first boosted car handed down from my bro and I really doubt turbo cars uses that much gas even redlining it.

What I've noticed:
-10-12mpg barely going into boost but letting the car idle for 5-10mins to get to normal operating temp when starting it, depending
-No strong fuel smell from the motor running
-Car hesitates in power sometimes while turning
-Car lost alot of power but its because of a blown turbo (car feels n/a)
-I see blue sometimes a hint of white smoke during every other idle
*blown oil seals on turbo = blue smoke, but maybe that hint of white smoke = unburnt fuel???
-RPMs fall down to 300-500 after every load when i brake or put the car in nuetral and slow down (either one, maybe both, can't recall)
-Compression test all 140, Leakdown test less than 8% leakage per cylinder

What I think:
-The car is basically a stock SR with FMIC, the car is running rich because of the walbro 255 fuel pump and bov is not recirculated, but can't be the reason for very very low mpg
-RPMs drop down maybe because of a bad brake booster causing a vacuum leak, or the atmospheric bov messing with the MAFS.

What I've found:
-Leaky injectors? is the closest thing I've found, but I don't know the symptoms of that besides the heavy white smoke in the exhaust. Could this likely be the problem?

I'm not going into the eng/mech field but into computers so I'm not too experienced in that but i do try. I've searched but I haven't seen any DIYs of how to test leaky injectors so if someone can help me out. Links or Writeups, very specific (from taking out the neg side of battery to when to start the car etc)

Thanks Zilvia members!