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2015 XT Touring CVT
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129 Posts
Discussion Starter #1 (Edited by Moderator)
2015 FXT 80k running cobb OTS stage one 91 map.

Engine MODs: GFB BPV

Getting a random knock around 2k RPM relatively consistantly at least once per drive. Knock is -5ish in feedback knock and fine knock learning. DAM drops to .875 but returns to 1 after a bit of driving after. I was running the 93 map, but with the knock brought it down to see if that helped but it hasn't. I continue to put 93 in but run the 91 map. I'm still getting the knock with the 91 MAP. Its been 3 tanks or so at different gas stations so think I can rule out bad gas as the cause. Any pointers on where I should look for issues or thinks to try? When it knocks the car sort of bucks.

Thanks
 

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2014 2.5i Limited CVT
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375 Posts
I think that there ** MAY ** have been a discussion on this site somewhere and may have been a TSB or such from Subaru about that same type of issue.

I was doing some deep searches a while back about a similar issue on my 2014 Foz 2.5 Limited (non-turbo) that has a similar issue - odd knocking sound in that 1700 to 2500 RPM range when accelerating - and even spoke to the dealer multiple times about it - was finally told "normal engine sounds" ...

I saw someplace online about somebody cleaning the MAP sensor and it going away...?
 

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2015 XT Touring CVT
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129 Posts
Discussion Starter #3
Thanks I'll try cleaning the MAP sensor. I was planning to install a catch can this weekend but wanted to hold off until I could figure out the cause. I saw some WRX owners just splash in some E85 when they fill up, but that's not a fix just a bandaid.
 

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2015 XT Touring CVT
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129 Posts
Discussion Starter #4
Pulled the MAP and MAF sensors this weekend and gave them a good cleaning with some electric cleaner. Still have the same knock when accelerating/cruising around 2k. Thinking of flashing back to stock and seeing if its the cobb OTS tune. Any ideas before i try that?
 

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2001 Forester STi 6spd with MapDCCD
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4,641 Posts
The knock and DAM systems on the newer generation ECUs tend to be far more pro-active and predicting than the ECU's of previous (EJ) generations.

With that said, on just about any Subaru ive work with, you are going to encounter noise being picked up at low rpm / low loads that may not even be real knock events. Things like brackets, heatshields and other items under the hood can often trip a false signal if they tend to rattle or vibrate, esp as a car ages and racks up the miles. In terms of it being actual knock at that RPM, its very unlikely. Knock becomes a concern as you apply a higher load to the motor and see some feedback populate the screen.


Cleaning MAF sensors only goes so far. One thing i would recommend is a good injector cleaner and look into having an cleaning of the intake tract done. The intake valves on D.I.T motors have the tendency to build up gunk and carbon, and carbon deposits can hurt in the long-run , and will even lead to knock events if left unchecked. There is a service called "wallnut blasting" to clean it out, but the local dealer by me actually just uses a sea-foam type of spray that breaks the gunk up. My wife's 17 outback had it done when it hit around 60k miles and it made a literal jump in MPGs and general operation. The smaller 2.0's arent much different.
 

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2015 XT Touring CVT
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129 Posts
Discussion Starter #6
Thanks, I did think of that and the CRC past oil change maybe a month or two ago. Maybe I'll run something through the tank for the injectors.
 
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