Big knock at low load.

I recently purchase a 05 wagon MT. I am in the process of getting parts together so I can get it in to Dave at cryotune for a stage 2 tune on his dyno.

 

In the mean time, I am trying to get the car as sorted as I can.

 

I flashed the stage 1 cobb map, I am running completely stock other than a "twisted motion" vf52 that is getting replaced with a oem take-off soon.

 

I ran to the hardware store and recorded a few logs, just to see how things were. Things were going well until my drive home, which was a very casual drive in medium-heavy traffic.

I registered 4 knocks, big enough to drop the DAM to 0. All knocks happened around 2500 rpm, 0-2 psi boost, calculated load around 1.0.

 

I am running cheap gas, still 91, but from a cheap station. I understand that there are other sources of noises that can trigger the knock sensors, but these were BIG knocks.

 

Can worn suspension components, loose heat shields and things like that cause knocks these big?

 

I really want to get this figured out before I take it for a tune.

Vf52 with OTS map es no bueno. Stay out of boost if at all possible until you get the OEM takeoff installed or until a proper tune can be performed with your specific mods. Fwiw, when I started seeing low load knock that was enough to kill IAM, it was the result of a cracked ringland. There's still a bunch of other things to check before jumping to that conclusion like loose heat shields, faulty knock sensor, anything rattling.

Vf52 with OTS map es no bueno. Stay out of boost if at all possible until you get the OEM takeoff installed or until a proper tune can be performed with your specific mods. Fwiw, when I started seeing low load knock that was enough to kill IAM, it was the result of a cracked ringland. There's still a bunch of other things to check before jumping to that conclusion like loose heat shields, faulty knock sensor, anything rattling.

 

So your car wasn't having det, it was a mechanical sound from the lapland?

 

The engine is freshly rebuilt, by some guy...... So I'm not ruling anything out. I am going to yank the motor to swap out the upipe, and it sounds like I need a throw out bearing too. So I'll check the compression and leak down while it's out.

 

I'm just looking for ideas of other stuff to check while it's out.

Correct. Mine was picking up noise at low load low rpm that couldn't be explained until performing a compression test, and disassembling the motor. If I'm not mistaken, improper piston to wall clearance can also cause piston slap which may give phantom knock.

 

This picture illustrates the beginning of my many poor financial decisions [emoji38][emoji38][emoji38]

So your car wasn't having det, it was a mechanical sound from the lapland?

 

The engine is freshly rebuilt, by some guy...... So I'm not ruling anything out. I am going to yank the motor to swap out the upipe, and it sounds like I need a throw out bearing too. So I'll check the compression and leak down while it's out.

 

I'm just looking for ideas of other stuff to check while it's out.

Why are you pulling the engine? What's wrong with the TOB?

Why are you pulling the engine? What's wrong with the TOB?

 

Well, I read the procedure for changing out the up-pipe and it sounds like I'd be half way to pulling the engine anyway, so I might as well do the timing belt and water pump, make sure the banjo filters are out. Supposedly when the engine was rebuilt it got manly rods, npr pistons and arp head studs, I want to pull a valve cover and at least verify the head studs.

 

I can hear a very slight grind when coasting in 1st at low speed with the clutch engaged.

If you need to do that stuff, then go ahead; but I wasn't anywhere near pulling the engine when I replaced my uppipe...

Not sure what procedure you read, but swapping the UP is nowhere near pulling the engine. If a stock catted UP is involved, you will need to loosen the passenger engine mount and shift the engine up 1/2".

 

It makes no sense that a rebuilt engine would have been installed with the old TOB and timing kit. Just sayin.

Not sure what procedure you read, but swapping the UP is nowhere near pulling the engine. If a stock catted UP is involved, you will need to loosen the passenger engine mount and shift the engine up 1/2".

 

It makes no sense that a rebuilt engine would have been installed with the old TOB and timing kit. Just sayin.

 

I hear you, but the guys who built the motor also put a $400 turbo on it and a ebay intake, on the stock tune. Granted he was going to get it tuned once it was broken in, but still.

 

A long weekend of wrenching is worth the piece of mind in my book.

I can see that... :-D

If the TOB is grinding, a TSK would be a good idea.

I just installed a TSK 3 months ago and I hear some kind of grinding at fairly high load and low rpm. But it then goes away. Annoying.

 

Start at post #55: http://legacygt.com/forums/showthread.php/engine-rpm-related-vibration-felt-shifter-changing-gears-263917p4.html

 

Oops, threadjack

If the TOB is grinding, a TSK would be a good idea.

 

Is a TSK one of these: https://www.flatironstuning.com/p-2603-pdm-tranquil-tsk3-snout-throwout-bearing-and-sleeve-repair-kit.aspx

 

I am new to subaru's, trying to get up to speed.

Yep. The sleeve slides over the old chewed up tranny snout which the TOB then rides on.

I reset the ECU, grabbed a friend to watch the AP and went for a long casual drive, staying out of boost. The DAM started at .75, then a knock sent it to .625. about 10 minutes later it went up to 1.0 and stayed there for the rest of the drive.

 

I'm a little stumped, but I am not going to stress about it until I get the parts on, and the tune done.

Vf40 for sale.

http://legacygt.com/forums/showthread.php?t=268501