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05-03-2021, 02:48 PM | #1 |
Scooby Newbie
Member#: 109288
Join Date: Mar 2006
Chapter/Region:
NWIC
Location: Kenmore, WA
Vehicle:2018 Forester XT White |
18’ Forester XT FBK
Not new to the forum or subarus but haven't posted in a looooong time. Yes my user name was created when I was in my early 20's. Not proud of it.
I currently have a 2018 Forester XT. Bought it new and have roughly 47k miles on it. Recently I changed my oil and air filter and decided to install my AP that I bought 6 months ago that's been waiting to be installed. I flashed the Stage 1 OTS maps and began monitoring my drives with the Anxiety Port. Started noticing some FBK as low as -5.92 during light throttle usually between -5 and 5 psi boost. Never registered any FBK during WOT. DAM almost always stays at 1. If I let off the throttle it goes away and the moment I give it more throttle it goes away. Also this doesn't seem to happen until the engine is warmed up. Since I was at 46k I decided to take the 3-4 hrs to change my spark plugs and walnut blasting my intake valves to see if it would help. No difference that I can notice. From what I've been reading the FA20 is pretty sensitive to knock and FBK during low throttle in the -5 the 5 psi vacuum/boost range is normal, but how much FBK is acceptable? Is this as a result of the EGR? Vacuum leak? Boost leak? I do notice my AFR is 14-15. Does that seem high? I've attached data logs if anyone would like to take a look. I have a smoke test machine that should be here to day and a boost leak tester that should be here by the end of the week. If anyone has any insight it would be greatly appreciated. I also know Cobb OTS maps aren't the greatest which is why I plan on getting tuned later this month once I install my other supporting mods that have been sitting in my garage. Just want to rule out any issues so I don't run into problems during the tune. Mods that are pending installation and tune are TGV/EGR deletes, Perrin charge pipe, Grimmspeed EBCS, GS drop in filter and AVO Intercooler. Looking at either Ambot or making the drive down to Surgeline from the Seattle area. Datalog https://docs.google.com/spreadsheets...jE12Bs8WY/edit For reference here a list of mods and work I've done that could pertain to this issue Current Mods -SPT Catback -V3 AP Stage 1 Recent Maintenance Work -Oil change 500 miles -OEM Air filter 500 miles -OEM NKG Spark Plugs 200 miles -Walnut blasting 200 miles Thanks in advance for any help or feedback
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Last edited by Mr. REXified; 05-03-2021 at 07:06 PM. |
05-03-2021, 04:46 PM | #2 |
Scooby Newbie
Member#: 446029
Join Date: May 2016
Location: 510
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If FBK occurs at low load and not WOT then it's generally not super concerning. Your FBK is high and occurs frequently. I've never logged KS noise but I've never had this issue. I do see random noise spikes between cylinders 1,2,3 but 4 is clean.
I don't really see anything that really stands out in the log. AFR is fine. I would check the engine bay for rattles. Check for rocks or foreign objects. The bottom turbo shield is a good place to check. If you have access to E85, I would throw in 2-3 gallons to see if there is any improvement. It's one way to check for false knock. |
05-03-2021, 05:18 PM | #3 | |
Scooby Newbie
Member#: 109288
Join Date: Mar 2006
Chapter/Region:
NWIC
Location: Kenmore, WA
Vehicle:2018 Forester XT White |
Quote:
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05-03-2021, 10:39 PM | #4 |
Scooby Newbie
Member#: 109288
Join Date: Mar 2006
Chapter/Region:
NWIC
Location: Kenmore, WA
Vehicle:2018 Forester XT White |
Found a Chevron station 15 min from me that sells E85. Gonna stop by after work and throw in 3 gallons then top off with 92 and I'll report back.
Anyone else have any insight? Last edited by Mr. REXified; 05-03-2021 at 10:40 PM. Reason: Adding |
05-04-2021, 01:23 AM | #5 | |
Scooby Newbie
Member#: 446029
Join Date: May 2016
Location: 510
|
Quote:
Ethanol is a great octane booster... How did your spark plugs look when they were removed? Does it knock if you rev in park? Maybe you can have have someone lightly rev the engine while you listen around the engine bay for anything out of the ordinary. |
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05-04-2021, 02:24 PM | #6 | |
Scooby Newbie
Member#: 109288
Join Date: Mar 2006
Chapter/Region:
NWIC
Location: Kenmore, WA
Vehicle:2018 Forester XT White |
Quote:
So I put in almost 4 gal of E85 and topped off with 92 last night. Still showed a -2.81 on my short drive to work. When I was driving into work i heard a buzzing from the back. I pulled over and looked under the car and saw 2 cracks in the y-pipe of my Catback and one of the 2 cracks is fully separated all the way around. The cracks are at the flange that connects my right muffler. I have a feeling this could be contributing to my FBK. The crack is right behind my rear sway bar but I'm sure there's enough resonance to make it back to the knock sensor. I'm gonna swap my stock catback on tonight and see what happens. |
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05-04-2021, 05:54 PM | #7 | |
Scooby Newbie
Member#: 446029
Join Date: May 2016
Location: 510
|
Quote:
That would be interesting it's the cause of FBK. |
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05-10-2021, 09:43 AM | #8 |
Scooby Newbie
Member#: 487500
Join Date: Jun 2018
Location: Catonsville, MD
Vehicle:2018 WRX |
Pretty sure this is just a case of the ots map. You could try the stage 0 map or just wait until you get a proper tune.
I wouldn't go down a rabbit hole of chasing a problem that is probably non existent. |
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