Im kinda stumped at this point. ive spent days reading across the net looking for answers and it just leads to more questions
So the car is a 04 wrx. the previous owner did little if no maintenance on it. He installed some ghetto turbo back exhaust with a catless downpipe, and im guessing started throwing codes due to no tuning, so installed a cat into the downpipe.
I got the car around 140k miles on it. car had a CEL (which i think was a emissions code, i foget) Replaced the timing belt and did a catless up pipe at the same time which then made the code go away. Drove the car around for a few months and have noticed that im only getting about 150 miles per tank and that its only building 10psi, i tried to turn in the WG arm a few turns which made no change. This last weekend the car popped a P0420 code which i assumed due to the rich exhaust smell ment the cat was plugged up. I ordered myself a AP and then removed the rear cat from the car, during this time i sprayed the entire engine bay with carb cleaner with her idling to search for vac leaks and found nothing, and replaced the fuel filter. as of last night the car was still only making about 11psi and is getting poor mpg.
So at this point im kinda at a loss where to go next. Thinking maybe cleaning the MAF sensor and maybe replacing the front O2 sensor?
turbo back exhaust, no cats
All new fluids
new timing belt
new fuel filter