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Old 08-21-2012, 10:54 PM   #1
Ben11wrx
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Default Quick knock question

I've looked around and haven't found a definitive answer. I'm getting some feedback knock while driving normally of -1.4 about every 5 mins or so and sometimes goes to -2.8. The datalog includes this happening. I run Shell 93 gas and switched to a Stage 1 91+SF map to see if it would go away, but no luck. I have a Cobb intake with box and a nameless axleback. When it happens, there is a slight hesitation and was just wondering if this is a normal "tip in" incident or is something wrong. The log was taken on the 91 map.

https://docs.google.com/spreadsheet/...aYVVMVnc#gid=0

Thanks in advance.
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Old 08-21-2012, 10:57 PM   #2
Ben11wrx
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Default

Also this has been happening for a while now and have tried many different types of gas stations. I thought it had something to do with the heat of the day (95 degrees), but was able to check it out this morning (70 degrees) and it was still there.
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Old 08-22-2012, 12:43 AM   #3
Ben11wrx
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Heres a WOT log just in case. Boost is a little low cause its the normal map...for some reason i always have to use the HWG map and im at sea level.

https://docs.google.com/spreadsheet/...mN3FueWc#gid=0
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Old 08-22-2012, 02:56 PM   #4
Tripintaz
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It's normal even on a stock tune. Don't worry about it unless you are seeing it at full throttle and the Fine Knock Learn is incrementing.
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Old 08-22-2012, 06:01 PM   #5
Ben11wrx
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Ok I was just on my way home from work, watching my feedback knock, and while normally driving it measured -4.2 then went away. I would have ignored it but it made the car fall flat on its face like turning on multiple A/C systems. Here is a log from right after that measuring -2.8. I know seeing the -1.4 every once in a while is normal but is there any way of doing something about these readings or are they normal also. I just want to make sure that im not messing up my pistons from preignition.

https://docs.google.com/spreadsheet/...uQ2dVNWc#gid=0
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Old 08-22-2012, 06:14 PM   #6
Ben11wrx
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I'm also wondering if I should try the Torqued Performance map, or would it still be there?
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Old 08-22-2012, 10:17 PM   #7
Tripintaz
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It will still be there. It's not the tune. It's the knock sensor doing its job. Again, it is NOT a problem unless the car is incrementing Fine Knock Learning under heavy loads and WOT. A little burst knock here and there are low RPM part throttle is normal behavior. Stop worrying about it.
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Old 08-22-2012, 10:49 PM   #8
hutch959
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ok... here is my experience.

while running the cobb maps, i would see random knock all the time.
for example, on the drive home from work (15 mins), i would always see -1.4 at some point during the drive. Im not talking reaming on it... just normal driving.
This would be on a 91ACN map, LWG... runig 93 octane gas.

After the mikey botti tune. i never see knock .
i can drive hard... slow, normal... nothing.
0.0 everytime.

so is what you are seeing harmless?
maybe.
I just know after my tune. 0.

oh.. and also... i always knocked bad with the cobb maps with shell.
Mobil gas has been the best ive found so far
BP next.
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Old 08-22-2012, 11:35 PM   #9
Ben11wrx
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Ok thanks guys. I wish i would have never come across that Feedback Knock measurement.
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Old 08-22-2012, 11:57 PM   #10
bacalhau16
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Subarus knock sensors are very sensitive and can sometimes pick up noise and register it as knock. As trip said, its really not much to worry about here and there.
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Old 08-23-2012, 10:34 AM   #11
Tripintaz
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The Feedback knock sensor is doing exactly what it was meant to do. You will see various amounts of burst knock depending on temperature of the air and fuel in your take and even the type of gas you use. Burst knock that comes on real fast at -1.4 degrees and quickly disappears is absolutely normal. Even a quick burst of -2.8 and tapering to zero real fast at part throttle is just fine. It means the ECU is doing its job.

Now if you are starting to LEARN knock in where the Fine Knock Learning table is remembering a knock value and always applying it then you should investigate to see if its something to be concerned about. Even if the FKL keeps a -1.4 value somewhere at low rpm and low throttle isnt really much of a concern.

The time you SHOULD be worried is if you see Burst Knock and or FKL start incrementing and increasing at WOT. Then you have true detonation happening and the ECU is trying to combat knock. This could be due to bad gas or too much boost/timing in your tune. Now a REAL BIG concern is if your DAM changes to any other value than 1.0. Then your ECU is trying to protect the engine from damage by backing down the timing advance at all engine loads and RPM's.

So again, stop worrying about a little burst knock at low load, low throttle.
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Old 08-23-2012, 04:52 PM   #12
AuthenticAMD
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As everyone has said, low load knock is fine as cylinder pressures are not as high in low load.
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