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Old 05-14-2021, 05:54 PM   #1
ilovedemhotrides
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Default 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.
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Old 05-14-2021, 06:55 PM   #2
subaru_gc8
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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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Old 05-14-2021, 08:01 PM   #3
ilovedemhotrides
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Quote:
Originally Posted by subaru_gc8 View Post
uhh the O2 sensor that matters is not in the downpipe its in the header. chances are that is not your problem


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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Old 05-14-2021, 09:35 PM   #4
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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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Old 05-14-2021, 10:30 PM   #5
Chi_San
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Don't forget fuel. You could have a weak fuel pump, bad FPR, or a jammed up fuel line.
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Old 05-14-2021, 10:37 PM   #6
benflynn
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My $ is on the MAF.
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Old 05-15-2021, 08:31 AM   #7
ilovedemhotrides
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Quote:
Originally Posted by subaru_gc8 View Post
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


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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Old 05-15-2021, 08:40 AM   #8
ilovedemhotrides
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wrb

Default Cracked Downpipe

Quote:
Originally Posted by Chi_San View Post
Don't forget fuel. You could have a weak fuel pump, bad FPR, or a jammed up fuel line.


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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Old 05-16-2021, 12:08 AM   #9
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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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Old 05-16-2021, 12:27 AM   #10
djoye
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If you replace the MAF, go OEM or Bosch, don't use parts store brand.
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Old 05-16-2021, 03:32 PM   #11
ilovedemhotrides
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Quote:
Originally Posted by Unabomber View Post
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.
Thanks big Ron! I am supposed to be getting tuned in 3 weeks, on a basemap now. I am going speed density so will no longer be MAF based.

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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