Strange Knock Occurance

[boostcaboose05]

Finally decided to make a post after dealing with this issue for months.

Long story not so short - I bought a legacy gt wagon that was built by someone here on the forum a few years ago. It was built with a blueprinted ej25 and a few mods (listed below). Last March it was sold to someone who may have been a little in over their head and eventually decided that it wasn't the car for them. This is my second Subaru, but my first turbo one. I'm in college so I try to stick to a budget but I'm also not trying to cheap out on this thing. 

Engine Mods/specs:

- Remanufactured longblock (about 40k miles as of now) and stock heads blueprinted by a shop (balanced rods and pistons, etc)

- TGV deletes, Catless Uppipe, Cobb Intake, Cobb IC to TB coupler, IAG AOS, Gates Racing Timing Belt, Exedy Lightweight Flywheel + Stage 1 Clutch, DW65C fuel pump, STI FPR mod, Etuned in 2019

- Everything else is stock - namely, stock turbo and boost controller, injectors, downpipe, intercooler, etc.

 

Problem: I can't get rid of WOT knock. It's enough to be concerning but not enough to show itself. My Cobb AP often shows Feedback Knock to -6 and FKL follows usually to -2.00 or -4.00 in places. It's not consistent. Sometimes it is terrible and my DAM drops to 0.875 or worse. Sometimes a WOT pull reads 0.00 knock. My question is what to do next - I'll list what I have already done below. 

 

Already done:

- Previous owner replaced stock injectors with 750cc Deatschwerks - returned to used stock injectors (not flow tested but cleaned with fuel tank injector cleaner and crudely bench tested)

- All vacuum lines replaced with silicone (excluding the lines running to the turbo; they seem happy)

- Smoke tested intake, fixed any leaks that were present with old rubber lines

- STI FPR connected to BOV vacuum line and manifold port capped. 

- Previous owner had the racing version of the IAG AOS installed without getting it retuned (no PCV). I used a kit to adapt it to the street version that retains the PCV valve. 

- Bulletproof TMIC Mod. Aluminum C Channel with JB weld just to be safe.

- Car was tuned with a TurboXS 50/50 valve. Returned to stock BPV as it was causing a massive vacuum leak. 

- Timing belt was installed with the incorrect crankshaft gear guide which caused it to skip two teeth. Fixed and installed the correct guide (that was a close one...)

- Replaced MAF and front O2. Checked MAP sensor for accuracy. Cleaned the cone air filter. 

- Spark plugs were replaced 1 year ago by PO (NGK one step colder). 

- Added grounding straps from engine to battery negative 

- PO changed from the DW65c to an AEM pump with a much higher flow. Tested DW65c and reinstalled it with two orings.

- Checked downpipe for restriction and cleaned - looked clear. 

- Checked knock sensor and all heat shields. Knock sensor torqued to spec and angled correctly - resistance reads in range.

 

Test results:

- Compression: 140 135 140 135

- Fuel Trims: Hovers between -5 and +4. Adds fuel when in vacuum and removes when in boost, but that isn't always consistent

- Boost: -11psi at idle. Max is always about 16.3psi - car is tuned for 17psi. 

- Fuel pressure checks good and holds prime

 

So what should I do now? Maybe pressure test the intake again? Get the injectors flow tested?  Get a downpipe for a wideband O2 and a retune? I have made a few graphs from 3rd gear logs and they haven't really shown anything amiss except for the knock and drop in timing. 

 

Apologies for the lengthy post!

 

 

 

[Infosecdad]

Was it tuned for the DW740s?  The stock injectors are 550 and you would need to adjust the tune to account for that.

Also, if it's tuned assuming the 50/50 BOV will dump air, but that air is actually being returned, that may need an adjustment as well.

 

[m sprank]

You dont tune for a BOV.  If the car was tuned for 750cc and running stock, amazed it runs at all.  You skipped two teeth on the timing belt???  Oh boy.  Oh and FBKC is NOT knock.  Knock is the actual knock count.  That is when the knock sensor "hears" a noise and registers it.  Everything else is all part of how the ecu and tune interpret data and operate the vehicle.  There may not have been any issue at all, just normal operation that you dont understand.  You could have noise from the front endlinks causing the problem.  Sounds like your just throwing shit against the wall to see if it splatters. 

My frustration over spills after spending a weekend with a group of owners who actually understand there cars some and know when to ask for help before they replace everything.  You post no data, just say things "check out".  You replace parts with unknown condition used and expect some different positive result.  Troubleshooting is like climbing a ladder, you take one rung at a time.  I give up.  Time to go back to consuming all the beers left in my cooler after the meet. 

Edited June 19, 2023 by m sprank

[KZJonny]

12 minutes ago, m sprank said:

Time to go back to consuming all the beers left in my cooler after the meet. 

That's a lot of beer dude. I'll look forward to the half-drunken angry posts this evening...

 

OP: Know thy tune. You've got a lot going on there for a mainly stock engine etc..... For example, me and others here have had a bad time with the COBB intake on a VF40. It's just not warranted, and if anything causes problems.

I'd have to guess that whatever tune you have was designed for some of the bits you've since changed. Injectors (as Infosecdad already said) would be the big one I'd look at, fuel pump as well. Between a lower flow pump and smaller injectors you could be a LOT leaner in places than you ought to be. I would humbly suggest starting by finding a tuner and having all those disparate parts checked out on a dyno or with some logged data. Get a baseline, figure out what might be your issue and zero in on that.

[m sprank]

Wife pooped the cooler this morning.  No words.  Just "the look".  Good times.  Maybe I head down to the hardware store for a funnel, 1" tube and a ball valve.  I have a good tree out front for one man beer bong adventures.  Posting pix of comatose Mike on the way to the hospital for a stomach pumping. 

[boostcaboose05]

1 hour ago, KZJonny said:

That's a lot of beer dude. I'll look forward to the half-drunken angry posts this evening...

 

OP: Know thy tune. You've got a lot going on there for a mainly stock engine etc..... For example, me and others here have had a bad time with the COBB intake on a VF40. It's just not warranted, and if anything causes problems.

I'd have to guess that whatever tune you have was designed for some of the bits you've since changed. Injectors (as Infosecdad already said) would be the big one I'd look at, fuel pump as well. Between a lower flow pump and smaller injectors you could be a LOT leaner in places than you ought to be. I would humbly suggest starting by finding a tuner and having all those disparate parts checked out on a dyno or with some logged data. Get a baseline, figure out what might be your issue and zero in on that.

 

I’m hoping to finally get some good logs that i can post here. Thanks for the suggestion! 

 

A little clarification though - I understand that it would have been ideal for my to start a thread when i first got the car. With that being said, everything i have done has been an iterative change and many parts like the O2 sensor, etc were new in box that i was able to source from people at my school. 

 

Through this whole process i have been in touch with a couple tuners and the original owner who have been gracious enough to lend me a hand. 

 

On the tune side of things, every part i have replaced has been in an attempt to return the car to the state that it was in when it was tuned. Everything from the injectors and fuel pump to the competition catch can were added by the last owner who was somehow unaware that these changes would need a tune. Because of the issues with COBB accessports and the fact that the car has been screwed with so much i have been hesitant to get a retune. 

 

Of course i was unaware that it had so many issues when i bought it last november, and am amazed that it ran at all. 

[m sprank]

This story is "why not to buy a 4th gen LGT". 

[KZJonny]

4 minutes ago, boostcaboose05 said:

Everything from the injectors and fuel pump to the competition catch can were added by the last owner who was somehow unaware that these changes would need a tune. Because of the issues with COBB accessports and the fact that the car has been screwed with so much i have been hesitant to get a retune. 

 

Ahhhh.

Yeah. That makes a lot more sense now. Don't get this place the wrong way, I joined up when I got my GT like... 8 years ago. and really just started getting involved a few years ago. The number of stories we see that are like yours, only completely clueless is large. "Why don't mah car done run right?"

Again, only a personal opinion, but since you know you have a tune (TGV deletes must have been adjusted for, and I do not think and OTS maps can do that....) I would suggest picking the running gear you want to have on the car, and delete the rest. Go get tuned. Nowish, or sooner.

Maybe you're safe with the tune in the car and the mods that you have. Maybe you are not. Maybe you spend a few hundo now to find out, or maybe ynansb a month from now. At very least a base tune will give you a starting place that you can safely drive.

Not saying it will come to that, but it could, and without having a good tune in there, not one person here can really say one way or the next. $6000>>>>> $300