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Help, feedback knock at low load/rpm


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So my car is a 2005 Legacy GT. It has an ej257 in it with CP pistons with 10k on the build. I have a Cobb short ram intake, catless up pipe, invidia catted downpipe and a unknown catback. I am currently running 91 octane stage 2 w/intake on my accessport. This is the generic tune from Cobb. It started hesitating around 2500 rpm and I decided to do some logs on my accessport, the results are not pleasing. I appear to be pulling feedback knock and Fine knock learn all over the place... Any idea on what could be wrong? I bought the car a month ago and it ran great. I had a leakdown test done and it ranged from 1-5% so i wasn't worried. All of a sudden it started stuttering. All i've done was changed the oil and filled up with 91 octane. I did change the spark plugs last night and that didn't help.

 

https://docs.google.com/spreadsheet/ccc?key=0AoFz3gVEgWFcdF9SQU0tbjVaM2piMzVZdFRnRTFpSWc&usp=drive_web#gid=0

https://docs.google.com/spreadsheet/ccc?key=0AoFz3gVEgWFcdFJkYXhjUWtlbjdvYTJyTWY2TUo3TUE&usp=drive_web

https://docs.google.com/spreadsheet/ccc?key=0AoFz3gVEgWFcdGlxWHlwVktYal9TX0s3TkVSNUdNeHc&usp=drive_web

https://docs.google.com/spreadsheet/ccc?key=0AoFz3gVEgWFcdEtOUEZYUU5BMFh1aFJOenI4cFlBdGc&usp=drive_web

https://docs.google.com/spreadsheet/ccc?key=0AoFz3gVEgWFcdDI0clltS0dhSWlfSmlYblNWdlltcmc&usp=drive_web

 

I don't have a log for high speed cruising, but i'm getting no knock when cruising on the highway. I do have forged pistons that slap, could that be causing false knock? Here are pictures of the spark plugs I pulled out. They have about 10k miles on them. Oh yeah I have a cracked bpv that is ghetto rigged back together with super glue til I get a new one. It appears to have been broken and ghetto rigged back together. This is what happened when I was checking loose connections.

 

http://imageshack.us/a/img812/2003/4zvr.jpg

http://imageshack.us/a/img20/6063/esg6.jpg

http://imageshack.us/a/img850/9431/mayt.jpg

http://imageshack.us/a/img69/9518/q05j.jpg

http://imageshack.us/a/img191/5884/ctvg.jpg

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Please, for the love of god, attach your pictures AND the log (which I can't even open) to your post. Go into the advanced editor and press the button for attachments. Telling us what car and mods (if any) you have would be a good start too.
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First post is updated with missing info/incorrect info. My brain is fried right now and i'm not thinking straight. Sorry for the misleading information.

 

Update: found out my intercooler is leaking by the turbo connection. Good thing I have the bulletproof kit on the way. I will be picking up an air compressor soon so I can do a boost leak test.

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That is a crapton of knock. I wouldn't be driving that car around until you can figure this out. You can start by replacing all your broken crap (sorry, no offense, but it's broken, it IS crap) with working stuff.

 

BP can help prevent it, but if the leak is bad, I wouldn't depend on it to fix your TMIC. Might want to source a used stocker from somewhere for cheap (classifieds here, or junkyard).

 

Replace your BPV. Immediately. Do not pass go.

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  • 4 weeks later...

Update:

 

I changed the knock sensor and that seems to have improved things a bit. Around town driving is about the same, stuttering around 2-3k under mild throttle. But I did a 3rd gear WOT pull and things looked pretty damn good.

 

Here are two wot pulls. I will get some around town logs soon.

 

https://docs.google.com/spreadsheet/ccc?key=0AoFz3gVEgWFcdGJ5d3hPWm1jUmtnejZPblFVeWRTRUE&usp=drive_web#gid=0

 

https://docs.google.com/spreadsheet/ccc?key=0AoFz3gVEgWFcdGJiZGYyLUFGR2k1Yk9ieWU4NVhqblE&usp=drive_web#gid=0

 

What could be causing the low rpm stuttering? What should I look into next? I have a wideband that I will be installing soon, just need to get a bung welded into my downpipe first. Here's a reminder as too whats been done.

 

Replaced spark plugs with NGK Iridiums

Replaced broken BPV with oem 08 LGT replacement

Boost leak test done and found torn inlet; replaced and tested to 10psi with no leaks

Pressure tested fuel lines before and after FPR; both pressures appeared to be correct

Replace knock sensor

 

No CEL

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Hmmm.....how about clean throttle body? Front O2 is good? These cars have a LOT of issues that develop from the front O2 sensor starting to go bad without setting a CEL. Maybe if you know someone that has a known good front O2, you could borrow it and see if it helps.
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Hmmm.....how about clean throttle body? Front O2 is good? These cars have a LOT of issues that develop from the front O2 sensor starting to go bad without setting a CEL. Maybe if you know someone that has a known good front O2, you could borrow it and see if it helps.

 

I'll look into that. Do you happen to know if the o2 sensors are different between the lgt motor and the ej257? As far as I know i'm running the stock ecu with the ej257. My accessport is for a lgt so I would assume my ecu is stock. Just trying to figure out what year/model I need to get the sensor for. Buying a car with a swapped motor is fun! lol

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update:

 

Stopped at ziptie dynowerks in slc and they said everything looked spot on and that it could just be false knock from the pistons. They suggested I throw some 104 octane in and see if it has any effect on the knock. If it doesn't then either its engine noise or a hidden rattle somewhere. Those guys are great. They came out and spent 20 minutes or so helping me out with diagnosing the issue free of charge! These guys are a great shop.

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  • 2 weeks later...

Here are the latest logs that my tuner said looked ok. Fyi, I live at 4,500 sea level so my vacuum will be lower than normal.

 

1st one is a warmed up idle:

https://docs.google.com/spreadsheet/ccc?key=0AoFz3gVEgWFcdGpTR0hUVGE4UENUcUN5NTc5XzF2THc&usp=drive_web#gid=0

 

2nd is cruising around town:

https://docs.google.com/spreadsheet/ccc?key=0AoFz3gVEgWFcdEFWWFdDR2RURkVPUDFBTllVMkNRYWc&usp=drive_web

 

3rd is a 3rd gear WOT pull:

https://docs.google.com/spreadsheet/ccc?key=0AoFz3gVEgWFcdExlOGVtVVFfVEFhaTRQVWdJWUNGVGc&usp=drive_web#gid=0

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Update: Cleaned throttle body, no improvement. It was quite dirty though.

 

Check the MAP sensor (16) and filter (17) as well, see the yellow area below. Try to replace it with another that you know is good and see if it fixes the problem. But start with replacing the filter (17), it may be that the filter is clogged.

http://legacygt.com/forums/attachment.php?attachmentid=168284&stc=1&d=1385015813

 

Another thing are the donut gaskets (green areas) that has a habit of starting to leak, which causes bad idle.

 

Of course - if you have the EJ257 it may not be exactly the same items as in the picture, but I think you get the main idea.

manifold.thumb.png.25c0de1caae88f9301433e85bbb3776b.png

453747.png
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  • 2 years later...

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