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Old 09-19-2018, 02:13 PM   #1
2009LGT
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Default High feedback knock values on 09 LGT 5MT stage 1 93 oct map

I wanted to migrate my comment from another thread, so that I didn't keep hijacking it...

I've got a 2009 Legacy GT 5MT (~59K miles) completely stock except the stage 1 93 oct tune. I've only run the tune for about a month (before that it was completely stock). I always use 93 and try to stick to Top Tier providers (lots of QuikTrips in my area).

My DAM stays at 1.0 all the time. At first, fine knock learn stayed mostly at 0 and occasionally went to -1.4. The feedback knock would stay at 0 and occasionally hit -1.4 itself. But, I've seen it slowly change to hit -2.8 and -4.2 on occasion. Just a couple of days ago, though, I saw it hit -9.8 briefly and I was really concerned. On the drive home, it hit -6.8 at one point, and I was occasionally seeing it go up to around -3 before settling back to zero. The times it was going to about -3 I was in 5th, cruising at 65mph, on either relatively flat stretch of highway or occasionally a slight incline. The AC was on the whole time (I'm in North Texas after all), though I don't recall if it was on recirculate or not. When cruise would accelerate to get up the incline, it didn't rev very high, nor did I hear a lot of noise. My calculated load hovered around 0.4 g/rev most of the time home and occasionally might hit 1.5 or 2.

I can't tell why feedback knock suddenly hit -9.8 or if I should be concerned. And I'm really not sure what to check to see if it's a simple fix.

What should I check or do?
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Old 09-19-2018, 02:16 PM   #2
2009LGT
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@Jewbaru - I'll try the stage 1 91 oct map & run 93 oct.

What should I be looking for on AF learning/correction? I saw somewhere that +/-3% or 5% is fine. Do you concur?

I do have a log from the other day. One is for the case of 5th gear, 65mph, slight incline, AC on (probably recirculating?) where I got -2 to -3 on FB knock. I'll see if I can post a Google Drive link later.
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Old 09-19-2018, 03:53 PM   #3
Airboy
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High FBKC numbers like -11.x is usually caused by mechanical rattle/buzz. Welds on the up-pipe heatshield is a common failure point.
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Old 09-19-2018, 05:09 PM   #4
2009LGT
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Quote:
Originally Posted by Airboy View Post
High FBKC numbers like -11.x is usually caused by mechanical rattle/buzz. Welds on the up-pipe heatshield is a common failure point.
Is that mainly on OEM uppipes/heat shields, or aftermarket or both? And if I wiggle the heat shield, should it basically have no/very little play?
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Old 09-19-2018, 07:58 PM   #5
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Quote:
Originally Posted by 2009LGT View Post
Is that mainly on OEM uppipes/heat shields, or aftermarket or both? And if I wiggle the heat shield, should it basically have no/very little play?
OEM up-pipe heatshield. Shouldn't move if you push on it it. Tap it with the handle of a screwdriver and listen for rattle/buzz.
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Old 09-20-2018, 11:27 AM   #6
Mindriddle
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highest ive seen mine is about -8.5 but its never when im doing a log. I did hear some rattling down by my exhaust that I need to look into. Then again, my car freaking sounds like a tin can now with a catless downpipe, which is more annoying than a minor rattling.
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Old 09-22-2018, 01:50 AM   #7
2009LGT
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Default Tried stage 1 91 oct map

Per Jewbaru's suggestion, I did flash the stage 1 91 oct map. But, it stalled on me pretty quick. And I noticed the knock sum was incrementing really fast. So, I flashed the stage 1 93 oct map back for now.

I have seen it hit -11 again once. But, it's not consistent. I looked at AF Correction 1/3 and AF Learning 1 now. The correction has occasionally hit -23% / 25% for the min/max. But, it does seem to stay around 3-5% for the most part. Usually if it gets to 10% or so, it's during harder acceleration/deceleration and only briefly. I'd assume such #'s are fine since it's a sudden event from the ECU's perspective and it needs a second to adjust.

I still need to find some time to check the heat shield. I also want to do a sanity check on the spark plugs. I assume they're fine given it's got ~60k miles in 9 years, but I'd rather be sure.
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Old 09-27-2018, 02:06 PM   #8
2009LGT
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I went ahead and checked near the uppipe and couldn't move the stock shield.

I also did an oil change this morning (fully synthetic) -- last one was 7 months ago (only 4k miles), so I was due. I had them check and no leaks. So, no obvious signs of issues there.

I was reading a Grimmspeed page on the intercooler, though, and it mentioned too much heat could cause knock. So, if I do a stage 1 93 oct tune, is it possible there's enough extra heat through the OEM TMIC to cause such values?
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