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Discussion Starter #1
Okay, where to start? First off, this is my first post in any forum of any kind. Second, I am pretty new to Subarus. So there is much I don't know and a lot I need to learn. I've worked on a few cars myself and have done a couple of small things on my 2016 STI such as cleaning the MAF and the throttle body valve, replacing the air filter, and replacing a broken driver side engine mount, but I am far from calling myself a competent mechanic. There are also a lot of abbreviations and acronyms I'm not familiar with either.

With that said, I am having a major loss of power and hesitation issues. It started about a month ago before I moved from southern California to Oregon. After the engine had been running for a while (30 minutes or more) and driving I would have a major or complete loss of power over about 4500 RPMs. It would bog down and backfire. I tried to replicate the problem without boost by climbing RPMs slowly and at around 4500 it would not only bog down but completely lose power as if I wasn't even on the pedal. I had to let off the pedal completely and press it again to get any acceleration. So I cleaned the MAF and throttle body valve (noticing a small amount of oil in the intercooler, throttle body, and the boot connecting the turbo to the intercooler). This had me thinking I should get and oil catch can but I haven't installed it yet, as I've spent hours researching other people having similar issues and all signs leading to fuel pump, fuel pressure sensor, throttle position sensor, bad gas, dirty fuel filter, etc.

The issue seemed to mostly go away after cleaning that stuff and also buying an access port and flashing the stage 1 tune. Now that I am in Oregon I have just yesterday started getting this problem again, only worse. except it doesn't completely lose all acceleration like it did before. Just bad hesitation and it has no power at all. The only way I could get it home is to stay between 3000 and 4000 RPMs. Which would just barely give me enough to get the car going. I'm not sure what to log on the access port for this information. The AF learning1 and Af learning 1 c have gone up to about +10. I'm not seeing any surges or anything weird with the turbo. The closest thing I can find on forums is people having bad fuel pumps. I'm wondering if this is the issue. Fuel pump duty seems to cycle between 33, 66 and 100%.

A few days ago the check engine light came on for one of the sensors by the catalytic converter, I can't remember which one.

Shortly after I purchased this car used I had to get the engine rebuilt because of piston ring failure on piston 4. They did a full engine refresh but I didn't have any of these issues until 5 months after the repair and am now in Oregon so taking the car back to them isn't an option. I did speak with the guy when it had the initial power loss issues and he said fuel pump. I would assume the cat and sensor would be dirty from whatever particulates blew through the engine when it was having the piston ring failure, and that maybe these are separate issues from what I'm currently experiencing.

Sorry for the long post, thank you for taking the time to read.

Only mods are the access port and tomei catback exhaust.
 

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Could be anything.

Fuel pumps are an issue in VAs? never heard this.

Boost leak would be more common - especially since the issue is so dramatic.
 

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Shoot me a log of your car when the problem is happen and when it's not (if you can) and I'll take a look.

Where in OR are you? We're in Bend, happy to take a look. I have my doubts it's a fuel pump. Do you have a downpipe in the car or is it totally stock?

Josh
Okay, where to start? First off, this is my first post in any forum of any kind. Second, I am pretty new to Subarus. So there is much I don't know and a lot I need to learn. I've worked on a few cars myself and have done a couple of small things on my 2016 STI such as cleaning the MAF and the throttle body valve, replacing the air filter, and replacing a broken driver side engine mount, but I am far from calling myself a competent mechanic. There are also a lot of abbreviations and acronyms I'm not familiar with either.

With that said, I am having a major loss of power and hesitation issues. It started about a month ago before I moved from southern California to Oregon. After the engine had been running for a while (30 minutes or more) and driving I would have a major or complete loss of power over about 4500 RPMs. It would bog down and backfire. I tried to replicate the problem without boost by climbing RPMs slowly and at around 4500 it would not only bog down but completely lose power as if I wasn't even on the pedal. I had to let off the pedal completely and press it again to get any acceleration. So I cleaned the MAF and throttle body valve (noticing a small amount of oil in the intercooler, throttle body, and the boot connecting the turbo to the intercooler). This had me thinking I should get and oil catch can but I haven't installed it yet, as I've spent hours researching other people having similar issues and all signs leading to fuel pump, fuel pressure sensor, throttle position sensor, bad gas, dirty fuel filter, etc.

The issue seemed to mostly go away after cleaning that stuff and also buying an access port and flashing the stage 1 tune. Now that I am in Oregon I have just yesterday started getting this problem again, only worse. except it doesn't completely lose all acceleration like it did before. Just bad hesitation and it has no power at all. The only way I could get it home is to stay between 3000 and 4000 RPMs. Which would just barely give me enough to get the car going. I'm not sure what to log on the access port for this information. The AF learning1 and Af learning 1 c have gone up to about +10. I'm not seeing any surges or anything weird with the turbo. The closest thing I can find on forums is people having bad fuel pumps. I'm wondering if this is the issue. Fuel pump duty seems to cycle between 33, 66 and 100%.

A few days ago the check engine light came on for one of the sensors by the catalytic converter, I can't remember which one.

Shortly after I purchased this car used I had to get the engine rebuilt because of piston ring failure on piston 4. They did a full engine refresh but I didn't have any of these issues until 5 months after the repair and am now in Oregon so taking the car back to them isn't an option. I did speak with the guy when it had the initial power loss issues and he said fuel pump. I would assume the cat and sensor would be dirty from whatever particulates blew through the engine when it was having the piston ring failure, and that maybe these are separate issues from what I'm currently experiencing.

Sorry for the long post, thank you for taking the time to read.

Only mods are the access port and tomei catback exhaust.
This is your chassis of STI.

Sorry, what is VA?
 

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Discussion Starter #5
Stock other than the access port and catback exhaust. I've been looking at how to do a boost leak test but it looks like it requires some parts I don't have so I might just see if a local shop can do it. I'm in Grants Pass.
 

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Discussion Starter #6
Will the access port automatically log the essential data for this or do I need to make adjustments?
 

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We're a couple hours away but Subaru is what we do. We have an AWD dyno and we're a COBB pro-tuner. What was the exact code you got?

Stock other than the access port and catback exhaust. I've been looking at how to do a boost leak test but it looks like it requires some parts I don't have so I might just see if a local shop can do it. I'm in Grants Pass.
Yeah, pretty much. If there's something else we need I'll walk you through how to add it.

Will the access port automatically log the essential data for this or do I need to make adjustments?
 

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Discussion Starter #8
I'm not currently getting any codes. I cleared the P0420 code and put a bottle of cataclean in the tank, hoping it would resolve the issue as I'm not in a great financial position due to covid19.
 

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Looks like you're in I-mode since it's only making 7psi at WOT. The fine knock learning is through the roof and you're getting significant feedback knock a only 7psi. The timing is very low because of the FNL. A/F looks fine. Makes me think there is a mechanical issue. I would suggest a compression test and leakdown to get you pointed in the right direction.

59148
 
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