Tip in knock

[Tor]

I have tip in knock, like the examples in this thread:
http://www.ft86club.com/forums/showthread.php?t=62346

In my case, it happens when blipping the throttle during downshifts. E.g. cruising in 4th with 3500 rpm and downshifting to overtake. If I blip the throttle aggressively, then I get an audible knock like the video examples in the link above. I.e. it only happens in neutral.

Could it be corrected with adjustments of the transient tables mentioned in this thread?
http://www.ft86club.com/forums/showthread.php?t=50088

[strat61caster]

When was your car built? If it was after spring of 2013 it already has the changes mentioned in the second thread you linked, which really targeted downshifting at 5k+ rpm more than anything else. If your car has an aftermarket tune odds are good it also has the same corrections. Do you have datalogs for the knock or just your ears?

The two videos in the thread you linked imo exhibit two different noises, neither being tip in knock. The first video with the firecracker like noise sounds like fried direct injector seals, that person never found out what caused the noise and sold the car:
http://www.ft86club.com/forums/showthread.php?t=101051

The second video sounds like the electric throttle snapping open, not knock, which could be what you're hearing depending on how you do your downshift.
http://www.ft86club.com/forums/showp...20&postcount=3

Maybe it is knock, idk, but neither of those videos match up to what you describe imo. I get a dull pop sound occasionally on downshifts, it comes from the rear so I figured it was either a backfire (suddenly unloaded engine, excess fuel, pop) or some drivetrain noise, now that I have OFT you've reminded me that I should probably set it up to log for a bit on my next drive.

[Spuds]

Pretty sure that's not knock. Are you logging knock correction at those times?

I have the same thing, even on stock tune. Seems like just induction noise, as mentioned in update4 of the post you linked. When you blip the throttle, you are suddenly opening a port (throttle) across which there is a pressure difference. That creates a pressure (sound) wave.

If you have logs indicating you engine is correcting for knock on throttle blip, you may still have knock.

Edit, I'm on oft stage1 right now, but this exists on both stock and oft tunes. Just clarifying.

[Kodename47]

Are we aware that knocking doesn't actually sound like knocking but, like it's other name, pinging. It's usually a high frequency sound.

[churchx]

.. but those early ICE adopters probably loved knock knock jokes too much.

[Tor]

Hi,
Thanks for the replies. Yes, I can actually see it in some logs, but not all. MotoEast mentioned in the thread I linked that it doesn't always appear in the logs.

Anyway here is an example of cruising in 4th at 3000 rpm with 5.5% accelerator pedal. Then neutral, blipping the throttle to 100%. RPM rises to 4200 and simultaneously switching from 4th to 3rd. Coinciding with 100% pedal, there is -0.7 FBKC.

http://www.datazap.me/u/tor/tor-2152...om=11896-11914

The sound I am getting is best described as a very fine small hammer hitting a block of metal. Here found a youtube video of a Jeweler hammering. Kind of the only the ping, but without the knocking noise of the hammer.

I noticed it occasionally before, but very rarely. Now that the temps have risen to 25-30 deg C here (IAT 34.7 C deg in the log) it's quite frequently but always in the same scenario as in the log: 4th gear 3000 rpm, downshift to 3rd with 100% throttle blip. If I blip more gently there is no pinging sound.

The above scenario occurs quite frequently as this is the typical situation of going legal limit of 80 kph (50 mph) in 4th on country roads, catching up with the usual jerk that always drives 10 kph slower (70 kph + 4th gear = 3000 rpm) than the limit and then down shifting to overtake.

[Tor]

On second thought, maybe my mind is playing a trick on me. After listening several times to the sound in the video in the thread @strat61caster linked to it might sound more similar to the noise (at 4 seconds) in this video.

So not knock then? Could even be that the knock sensor is picking up the noise of the throttle?

[ame="https://www.youtube.com/watch?v=g8nnFeP7ib0"]Frs/Subaru Brz "tip in knock"? and VVT sound - YouTube[/ame]

[strat61caster]

Originally Posted by Tor

So not knock then? Could even be that the knock sensor is picking up the noise of the throttle?

I would have no idea, but the throttle noise is very easy to reproduce, just stab the gas pedal to the floor and you should be able to hear it in person. Whether you're in neutral or cruising or downshifting, it acts the same.

I'm totally inexperienced when it comes to pinging/knocking, but I do know this car makes a few quirky noises that are totally normal. The knock correction factor is curious though, I could see it being normal and I could understand it being a sign of knock.

[nikitopo]

Just for the story ...


I had an ECU tune in my Forester (FB20 engine). At first everything was fine, but eventually it started knocking in tip in enrichment. Then it started knocking in other conditions, started smelling burn and afterwards started to burn oil. I had to re-fill oil every 3000-4000 km and I was very close to blown up the engine. My tuner couldn't help me. I don't blame the tuner because the changes were minimal. I decided to flash the ROM back to stock and left the tune to balance the parameters. Afterwards, I used a carbon build-up chemical cleaner. After 4 years the engine still goes fine, remains strong and the knock issues disappeared.


I never had an ECU tune in my BRZ (FA20 engine). One of the main reasons the bad experience with my Forester. I am might be wrong and it might be the engine, but it is my car and it is me that will pay if something goes wrong. Result: I never had a knock in my BRZ.


P.S.: I am using in both cars V-power racing just for the peace of mind.

[Tor]

Well, now I played the videos over and over again, and I would say mine sounds worse than the video above. More like (but not as bad) as the supercharged white car.

Also, I don't get the sound by just blipping the throttle 100% at standstill. Yes, there is the induction noise, but there is another noise on top of it (that metallic noise) in the downshift scenario.

Sorry, it's very difficult to remember and describe a sound. I had the car for 2 1/2 years now and didn't notice this particular sound before.

[Rezi]

Originally Posted by Tor

On second thought, maybe my mind is playing a trick on me. After listening several times to the sound in the video in the thread @strat61caster linked to it might sound more similar to the noise (at 4 seconds) in this video.

So not knock then? Could even be that the knock sensor is picking up the noise of the throttle?

Just a idea: Do you have AC on? It is shut off when going WOT. I also wouldn't believe thats real knock. Those guys on stock ecu with much worse fuel would had reported it.

[Lantana frs]

My ac is a noisy sonofabitch too. Especially when car is up to temp.

[Teseo]

Mine does it. Its called shit gasoline. After that i use nothing but 93 oct gas and everything its fine

[steve99]

From my experience its very difficult to hear knock on these cars unless its rearly bad like _2or-3 degrees of correction in logs and its almost impossible to hear at mid to upper rpm usually you can only hear it below say 4000 but it neds to be rearly bad.

Id ve very sceptical that what your hearing is knock if the only info in logs is a small -0.6 correction.

The only time ive heard knock is usually on stock tuned cars

Try adding some octane booster or try 5 litres of e85 in full tank and see if it makes any difference to noise or logs.

Knock sensors can be fooled by mechanical noises common one is overpipe hitting on subframe or anti roll bar

Now if your log looked like this stock tuned car you might hear the knock

http://www.datazap.me/u/steve99/sout...=1477440000000


Also have a look at the transient ignition retard table from the stock K00C 2017 rom, much more agressive than the older roms, note the table size is different.


.