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Mystery knock hunting.


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I'm pretty new to the forum but I've been lurking for about 8months now so I'm aware there are TONS of knock threads, but I haven't been able to solve my problem thus far so I figured I should start another.

 

I have a 2005 LGT manual, I bought it back in December with a "new motor and turbo" installed in it. I say that in quotes because I eventually found out from the shop that did the work that it is not in fact, a new motor, it was just swapped from another car (that pissed me off) the turbo is new however. So that's the patient.

 

About a month ago I grabbed a cobb accessport and happily loaded up the stage 1 91 octane tune with 93 in the tank. That's where all my problems started

 

I did a few datalogs the day I got it, and noticed something terrifying. I saw upwards of -12 feedback knock, and a max of -10 fine knock learn! But strangely my DAM stayed at 1. Doing a third gear pull results in everything going back to zero, no fine knock, no fine knock learn, if I let off the gas during a pull I get -2 feedback everytime. (not too concerning).

 

Talking with Cobb they essentially told me I have nothing to worry about because it's relatively low load, usually around 1.1 is the highest it will "knock". However, -10 fine knock learn essentially makes the car useless, it jerks and jolts and drives like grab when pulling that much timing, so regardless of its dangerous to my motor, it's annoying as hell.

 

Recently I've been running the installed stock tune instead, and it never learns as much knock, tops -4 learned, and the most I've seen in feedback knock is -8. So it seems to me it can't be false knock if there's a large difference between the installed stock and stage 1? Also, recently on the highway, my DAM randomly jumped from 1 to 0. I panicked, pulled over, reset my ecu, and it hasnt dropped again.

 

I've replaced the front AF sensor and my TMIC because that was leaking slightly. My front heat sheild was loose but I tightened it with a hose clamp. I replaced all 4 spark plugs as well.

 

I'm frustrated and discouraged and I'm hoping someone has ideas for me. It's been to a subaru specialist already and they said they didn't see anything wrong with it aside from pulling timing.

 

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If everything is good mechanically (and you're sure), then it's tune related, plain-and-simple. If "pulling timing" isn't something wrong, I'd go see a different Subaru specialist, personally. A proper tune shouldn't pull timing besides maybe some FLKC on sharp transients (tip-in/lift-off). A proper tune shouldn't ever have any learned knock assuming everything is sound mechanically (no loose heatshields, etc.).
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I would agree with you except I feel that something either mechanical or sensor related must be an issue here as it does this on the stock tune as well!! (just not as bad) I'm basically looking for ideas on what to check. I initially though I had a boost leak but my af learning is never above 4.

 

2005 LGT MT stage 1

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Unfortunately, the only way to test the MAF is to replace with a known good one. I hate parts swapping, but. If you buy a new one, Denso ONLY.

 

http://people.csail.mit.edu/ilh/vacation/

The fuel pressure test procedure is in here. Unlikely to turn anything up, so probably not worth buying a fuel pressure tester if you don't have one. Oh, and don't get the Harbor Freight tester, it's crap.

 

I know you said your A/F learning is never above 4, but just to verify, can you post your AF Learning A-D values?

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Have you completely checked for any air leaks in your intake? From the airbox MAF through to the TGV's, make sure there aren't any leaks. Double check all the hoses for cracks or bad seals. There's a ton of hoses and just one of them being loose or damaged will cause all sorts of problems. Since everything's been disturbed by an engine swap, there's a good chance something was overlooked.

 

 

Also check for exhaust leaks at the manifold or to the turbo.

 

I started getting some random FLK last week and found that my oil filter had backed off a turn and was leaking slightly. Tightened it and the FLK went away. These engines are super finicky with any sort of leak.

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Did a boost leak test and didn't notice anything, I used my compressor and soapy water. The noise from the air rushing through the throttle body and out the oil cap was pretty loud so I couldn't hear anything else, is there a way to get around that? Also if it helps at all, the "knock" never occurs until the car is 100% warmed up, like I have to drive for atleast 10 minutes before anything shows up.

 

2005 LGT MT stage 1

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Yea i will definitely do that this afternoon. I was able to get this by just revving my engine while sitting. Right after I took this photo I got it to hit -12 just by revving. Is it even possible that's actual knock? It even started to learn some with me revving it. e34b859b82eac418544e505c3d290d63.jpg

 

2005 LGT MT stage 1

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I'll have to find someone to swap mafs with, the readings from it look good though, and I cleaned it off twice. I noticed that when I Rev up to about 4k, I get a loud buzzing that seems to reverb through the gear shift. Any gear, it does this, I've checked all the heat shields and they aren't loose. It definite ly seems like something is loose and could also be the cause of my knock. But I can't find it!! Are there any common places that rattle besides exhaust heat shields?

 

When I had the intercooler off to check the knock sensor (it's in the right position) I noticed two other things: there's oil in my intake track, the turbos new so bad pcv? and maybe the oil is detonating at low loads? I also noticed that the rubber grommet if you call it, on the clutch fork was popped off, tried to put it back in but I wasnt able to. Not sure if that would let more noise out of the tunnel or something (I'm pulling at strings.)

 

Thanks to all for following my wild goose chase! I have a couple days off this week so I'll be wrenching and swearing for both of them! Plan to do a compression test as well.

 

2005 LGT MT stage 1

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Chasing rattles/buzz is a good idea. I was also just reading a thread where this was caused by a bad knock sensor.

Keep at that grommet, could be the source of your buzz. Been a while, I don't remember if you have to take off the slave cylinder.

Oil in the IC-TB hose etc. is normal, if it seems excessive check your PCV valve.

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Checked a few things today, changed the oil, checked the knock sensor with a multimeter, cut off a loose rust bolt I found that was just dangling. And I went out and did some log pulls. Then this happened

 

 

Is that my clutch? Or bearing? I'm pretty sure my bearing was already making noise (I have another thread open about this) but I'm wondering if it's all connected at this point.

 

2005 LGT MT stage 1

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Checked a few things today, changed the oil, checked the knock sensor with a multimeter, cut off a loose rust bolt I found that was just dangling. And I went out and did some log pulls. Then this happened

 

 

Is that my clutch? Or bearing? I'm pretty sure my bearing was already making noise (I have another thread open about this) but I'm wondering if it's all connected at this point.

 

2005 LGT MT stage 1

 

That sounds like a boost leak. Right at the end, did you let off the gas and push in the clutch or just let off the gas?

 

Did a boost leak test and didn't notice anything, I used my compressor and soapy water. The noise from the air rushing through the throttle body and out the oil cap was pretty loud so I couldn't hear anything else, is there a way to get around that? Also if it helps at all, the "knock" never occurs until the car is 100% warmed up, like I have to drive for atleast 10 minutes before anything shows up.
Describe your testing proceedure. There should not be any air leaking from your intake. Your oil cap should be tight. You're simulating boosted air pressure from your turbo to how the engine would see the pressure while running.

 

I built this to put in my intake and pressurize from my air compressor.

 

attachment.php?attachmentid=266217&stc=1&d=1529429144

 

I can pressurize my entire intake through to over 20psi before I can detect any minor air leaks:

 

attachment.php?attachmentid=266218&stc=1&d=1529429144

 

I have discovered air leaks everywhere, even after replacing the entire engine. Basically any part that I reused from my old engine was garbage. All new hoses. You will even pick up FLK if your oil pan is leaking. They are that sensitive.

 

I started getting minor FLK the other day and discovered that my oil filter had backed off a turn.

 

If you are serious about getting your car to run properly, then be prepared to replace every single hose and pull everything apart.

 

Is this fuse sopposed to be missing? The key says main fan...
Yes, there should be a 25 AMP fuse there for your fan.

Pressure_tester.thumb.jpg.851342000862df0f68688fe57e3ec399.jpg

20psi.thumb.jpg.1996f99ee3cff1ee7fa650f3bce46791.jpg

Turbo_foam.thumb.jpg.48116caf951b7f04d61c949c7fbace62.jpg

BOV_tube.thumb.jpg.c73f3e397a94720cdb62f591fe4487bb.jpg

PCV_tube.thumb.jpg.1b3e0e3e66bb501d1ba4c57da17de1b9.jpg

Ripped_hose.thumb.jpg.14209da611de4f41ef4c9ce0e1455926.jpg

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Thank you very much for that writeup, I'll give that a shot. Everyone was worrying me by saying my cam deals will blow if I don't open my oil cap. Is that not something I need to worry about?

 

On a side note, I just did a compression test. Engine is ambient temp, and all spark plugs removed. Does this look okay?

 

1 - 116psi

3 - 117psi

2 - 115psi

4 - 110psi

 

 

 

2005 LGT MT stage 1

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subscribed...

 

 

been suffering from a slightly similar issue (low load knock of ~-6 always around the same cells). Have yet to find the root cause :(.

 

 

https://legacygt.com/forums/showthread.php/time-identify-once-and-all-source-my-fkc-267740.html

I'll keep you posted! I've subbed to your thread as well. I've decided to pull the motor tomorrow as I need to do a throw out bearing I believe, along with easier access to my leaky steering rack. I'm gonna go through the motor on a stand and make damn sure it's good to go. The driver side valve cover gasket is leaking too so that will be fixed. Pray for me it doesn't rain for a few weeks, my backup is a motorcycle!

 

P. S the noise was probably not my turbo, took it off today and it has zero shaft play and no carnage.

 

2005 LGT MT stage 1

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P. S the noise was probably not my turbo, took it off today and it has zero shaft play and no carnage.

 

2005 LGT MT stage 1

 

Have you carefully inspected the throttle body hose between the intercooler and throttle body? The OEM one tends to separate at the ends. I had this happened to me before. But you could easily see that on the fuel trims (became way negative).

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