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05-14-2021, 05:54 PM | #1 |
Scooby Newbie
Member#: 326147
Join Date: Jul 2012
Location: Philly
Vehicle:2004 STI wrb |
Cracked Downpipe
My car is adding 25% fuel, and the tuning shop said that my Downpipe has a crack in it, which could be causing the issue.
I initially thought it sounds likely, but on second thought, I could see a cracked up pipe cause this but how would a downpipe cause this? They made it seem as if the car would suck in air from the crack and add more fuel. How would this happen from the downpipe , where gasses are flowing out of pipe rather than in. Am I missing something ?? What I've already tried: I cleaned out the MAF with MAF cleaner Replaced the 02 sensor with a new one Replaced spark plugs all around NOTE: passenger 2 cylinders were black and fouled whereas the driver side 2 were perfect. What does this tell us? Those 2 cylinders are running rich. Idk what this means on a Subaru though. Boost leak tested car- found bov leaking but I've been told turbo xs can leak under boost leak test. Either way I just ordered an hks bov and will install next week when jt comes in. Also has no check engine light so it makes it a bit harder.
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Last edited by ilovedemhotrides; 05-16-2021 at 03:34 PM. |
05-14-2021, 06:55 PM | #2 |
Scooby Specialist
Member#: 29292
Join Date: Nov 2002
Chapter/Region:
SCIC
Location: Orange County CA
Vehicle:2004 WRX wagon silver |
uhh the O2 sensor that matters is not in the downpipe its in the header. chances are that is not your problem
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05-14-2021, 08:01 PM | #3 | |
Scooby Newbie
Member#: 326147
Join Date: Jul 2012
Location: Philly
Vehicle:2004 STI wrb |
Quote:
Yeah that’s what I thought. If it was in the uppipe, it would make sense, but being post turbo this theory makes no sense. Ugh - I took it to the shop because I already replaced the 02, cleaned the MAF, and the only thing I found was a leaky BOV. Now I know what you’re thinking, the BOV (my guess too) but to play devils advocate, I heard turbo xs bov will leak during a boost leak test as there are no rings, thus causing poor sealing. Also this bov has been on the car for a few years and I can’t seem to think it wasn’t in a similar state prior to all this happening with the car adding a bunch of fuel. I ordered an hks bov so we’ll see if that fixes the issues I’ve been seeing |
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05-14-2021, 09:35 PM | #4 |
Scooby Specialist
Member#: 29292
Join Date: Nov 2002
Chapter/Region:
SCIC
Location: Orange County CA
Vehicle:2004 WRX wagon silver |
so there can be a few different things that could be a issue, it could be the MAF front O2 or just a post MAF leak. Its a little hard to do this from the internet, but if you do a boost leak that would be the cheapest place to start before you go throwing parts at it. BTW if your car is adding that much fuel its going to be pretty big leak
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05-14-2021, 10:30 PM | #5 |
Scooby Guru
Member#: 53558
Join Date: Jan 2004
Chapter/Region:
NWIC
Location: Deadford, OR
Vehicle:2005 Baja Turbo White/Silver/Black 3tone |
Don't forget fuel. You could have a weak fuel pump, bad FPR, or a jammed up fuel line.
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05-14-2021, 10:37 PM | #6 |
Scooby Specialist
Member#: 515308
Join Date: Jun 2020
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My $ is on the MAF.
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05-15-2021, 08:31 AM | #7 | |
Scooby Newbie
Member#: 326147
Join Date: Jul 2012
Location: Philly
Vehicle:2004 STI wrb |
Quote:
What I’ve already tried: I cleaned out the MAF with MAF cleaner Replaced the 02 sensor with a new one Replaced spark plugs all around NOTE: passenger 2 cylinders were black and fouled whereas the driver side 2 were perfect. What does this tell us? Those 2 cylinders are running rich. Idk what this means on a Subaru though. Boost leak tested car- found bov leaking but I’ve been told turbo xs can leak under boost leak test. Either way I just ordered an hks bov and will install next week when jt comes in. Also has no check engine light so it makes it a bit harder. |
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05-15-2021, 08:40 AM | #8 | |
Scooby Newbie
Member#: 326147
Join Date: Jul 2012
Location: Philly
Vehicle:2004 STI wrb |
Cracked Downpipe
Quote:
Fuel pump is new last year. AEM 340 I pulled off my fuel line and put the car In test mode, the fuel pump dumped out the gas pretty fast so I don’t think this is the issue FPR is interesting - mine is stock and I do plan on putting in the new one before my tune. But humor me, how would this be causing the issue ? Because it should be getting x fuel amount but it’s really getting 75%, so it’s adding more ? This seems like a stretch but anything is possible. |
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05-16-2021, 12:08 AM | #9 |
Big Ron
Super Moderator Member#: 18062
Join Date: Apr 2002
Chapter/Region:
MAIC
Location: I can save you a ton of cash
Vehicle:on car parts so PM me b4 j00 buy |
If your car is 5+ years old, REPLACE the MAF. So many think cleaning is the cure all. You can clean my dog's crap all you like, but its still crap. They go bad. Same with your BCS...if its more than 5, toss and replace with an OEM BCS from the dealer or aftermarket before your next tune.
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05-16-2021, 12:27 AM | #10 |
Scooby Specialist
Member#: 50072
Join Date: Dec 2003
Chapter/Region:
South East
Location: TN
Vehicle:2017 STI Blue |
If you replace the MAF, go OEM or Bosch, don't use parts store brand.
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05-16-2021, 03:32 PM | #11 | |
Scooby Newbie
Member#: 326147
Join Date: Jul 2012
Location: Philly
Vehicle:2004 STI wrb |
Quote:
I know now this could be causing my problem, and don't get me wrong I'm not saying its not the MAF. But, my logs seem like the maf is working correctly based on the voltage and maf reading per the log. https://docs.google.com/spreadsheets...it?usp=sharing Please dont' grill me if I'm wrong... but let me know what you think based on the logs. Also thinking could be the brake booster? |
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