04 WRX. Poor mileage, low boost
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This is a discussion on 04 WRX. Poor mileage, low boost within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Im kinda stumped at this point. ive spent days reading across the net looking for answers and it just leads ...

  1. #1
    Registered User Blackcloud556's Avatar
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    Question 04 WRX. Poor mileage, low boost

    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?

    Mods.
    stock intake.
    turbo back exhaust, no cats
    Cobb AP


    All new fluids
    new timing belt
    new fuel filter
    Jason
    Alligator Performance
    2004 WRX. No Kittys, Cobb AP
    2006 LBZ Duramax. 644hp

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    Registered User UEDan's Avatar
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    Re: 04 WRX. Poor mileage, low boost

    Ok you said you got the AP, but what map are you running? With a catless downpipe you should be on a stage 2 map.

    Edit: woops stock intake. Do you know how to datalog?

    Posted from a fone.

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    Registered User Blackcloud556's Avatar
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    Stage 2 91 octane tune.

    Im gonna pull it into our shop this afternoon and try to clean the MAF sensor. and ill try to get some data logging done tonight as well.
    Jason
    Alligator Performance
    2004 WRX. No Kittys, Cobb AP
    2006 LBZ Duramax. 644hp

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    \_(ツ)_/ Rambo's Avatar
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    Couple things:

    1. Cobb OTS map notes SPECIFICALLY state their maps are designed for catted downpipes ONLY. They are not designed for catless exhaust systems.

    2. If you're only getting 9-10 psi of boost, you're likely operating on wastegate pressure only. Does the car have any modifications to the turbo control system (manual boost controller, EBCS, etc)?

    3. Turning the wastegate arm more at this point is not doing your car any good. Turn it back to the stock position until you fix your boost issue, then evaluate if you're hitting target boost.

    4. You state the car came with a catless turboback, then you later installed a catless uppipe. You then throw a code and think a cat is plugged up, and you remove the "rear cat from the car"? That doesn't make any sense. If you had a catless turboback to start, then did the uppipe, you don't have any catalytic converters left to remove, so I'm curious what you actaully did remove. Check out this diagram of your exhaust system. With very few exceptions (Perrin being one), aftermarket "downpipes" replace both the "downpipe" AND "midpipe" sections in the diagram below, replacing the factory two-piece downpipe with one single pipe which is either catless, or has a single high-flow cat.



    5. I'm willing to bet the PO messed with you boost control circuit, so I'd look very closely at the boost control solenoid and all vacuum hoses connected to it and the turbo for any tampering. I would also get a tune more appropriate to your installed mods, or change your downpipe to match Cobb's OTS requirements.
    Isaac -- 2003 WRX sedan Stg II - Gave its life for mine 6/2013.
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    Registered User Blackcloud556's Avatar
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    ok so looking at your picture there. the previous owner removed the factory downpipe and midpipe. and replaced them with a catless downpipe. then he decided to weld a cat back into the system.. I thus removed the cat for good.

    Ive examined all the lines i can see for anything that looks out of place and have found nothing out of the ordinary. And i guess i can start looking for new maps

    Thanks
    Jason
    Alligator Performance
    2004 WRX. No Kittys, Cobb AP
    2006 LBZ Duramax. 644hp

  7. #6
    \_(ツ)_/ Rambo's Avatar
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    Quote Originally Posted by Blackcloud556 View Post
    ok so looking at your picture there. the previous owner removed the factory downpipe and midpipe. and replaced them with a catless downpipe. then he decided to weld a cat back into the system.. I thus removed the cat for good.
    Hmm, ok. That makes more sense I guess, that's just an unusual thing to do.
    Isaac -- 2003 WRX sedan Stg II - Gave its life for mine 6/2013.
    2007 Outback 3.0R wagon
    Proud owner of a N.E.R.D, Member 1.3810-23

    The pursuit of knowledge is hopeless and eternal... Hooray!!! - Professor Farnsworth

  8. #7
    Registered User Blackcloud556's Avatar
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    yeah.. My guess is that he removed the cat, and since he had no tuner it started to throw codes so he tossed one back on.

    All in all tho the MPG was in the dumps and boost was low long before i started to remove cats or put a tuner on it. Im gonna rig the shop compressor to it tonight and look for leaks
    Jason
    Alligator Performance
    2004 WRX. No Kittys, Cobb AP
    2006 LBZ Duramax. 644hp

  9. #8
    Registered User UEDan's Avatar
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    Re: 04 WRX. Poor mileage, low boost

    Going back to to the wastegate pressure possibility. Check the turbo outlet, there should be a little nipple going to a hose going to a T fitting. Then to the wastegate and then boost solenoid. Check for cracks and breaks and a hard restrictor pill.

    I just recently had to replace ALL my boost controller lines because they were worn, brittle and 1 line had a crack. 8psi of boost.

    I know you said you have already but.... picture?

    Posted from a fone.

  10. #9
    Registered User Blackcloud556's Avatar
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    Aight. ill look there.

    the diagram that was posted above is the picture i was talking about

    What should the MAF should be reading at stock, or the factory o2 sensors?
    Jason
    Alligator Performance
    2004 WRX. No Kittys, Cobb AP
    2006 LBZ Duramax. 644hp

  11. #10
    Registered User Blackcloud556's Avatar
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    Rogged up the intake piping up to the air compressor tonight, and found no major air leaks, Just found a buzzing and a small leak in some parts next to the alternator


    Then did a short data log when getting onto the freeway.
    Jason
    Alligator Performance
    2004 WRX. No Kittys, Cobb AP
    2006 LBZ Duramax. 644hp

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