Tip in knock
 

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

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.

:cheers:

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.

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.

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

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.
https://www.youtube.com/watch?featur...8D4d9naGg#t=60

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.

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]

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.

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.

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.

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.

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

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

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.


.

Steve, I don't think the issue is always the fuel quality. In Germany we have very high quality. When I had a similar issue in my Forester, I couldn't fix it even with V-power racing which is rated at 100 RON. The knock was for sure there, the engine was gutless and I could see it even in the logs. I believe that some engines are not so tolerant to changes and maybe the table definitions were not a 100% accurate. I don't blame my tuner (throttlehappy) which in fact was very good and I could also verify myself that the parameter changes were minimal and careful made. Nevertheless, I am a programmer and I can understand the whole process of tuning and its pitfalls.

I think that Tor is on his own and depending the cause of the problem he might solve the issue or not. Personally, I wouldn't take the risk and I would flash immediately the tune back to stock. I guess everyone is different.

The AC is off most of the time I drive the car. I'm using 100 octane fuel and have no other knock worth mentioning. The stock tune has tip in knock too. I'm not going back to stock because of (potential) knock in low load transients and only in one specific circumstance. This is not something that really worries me, more it annoys me.

Also I'm not too sure how much I trust the logs in this specific scenario, as MotoEast wrote that it doesn't always show up in the logs. I could imagine that the rapid change could make it difficult for the ECU to react and the logged values (if any) may not correspond with the actual severity. Of course that personal imagination/theory.

Thanks for the tip, Steve. Left is A01G, middle MY17 and right is what I might try out. Was it ever settled for sure if the offset should be -30 or -50? The definitions I have, say -50 for both the old and new ROMs.

https://s28.postimg.org/xf2y1m9bx/Sc...t_10.11.34.png

haha,


my reasoning here is to eliminate fuel quality, if you add octane booster or better fuel then theoretically knock should reduce. If it doesn't reduce at all then the cause may not be knock but a mechanical problem like exhaust hitting on chassis fooling knock sensor faulty or loose knock sensor or other mechanical noise being interpreted as knock :-)


or you have some other major tune issue or hardware issue causing for example a very lean condition.


for example incorrect scaling of 02 sensor. can cause you to run incorrect AFR but logging will show correct afr, always best to check with another independent sensor if weird stuff happening.


Flashing to stock is always a good check to do to eliminate hardware/tune issue, however not always possible if you have changed components that require "tune" or running say E85.

yes as long as scaling/offset is same in both defs should be ok


the more aggressive transient retard may dull on/off throttle response

I agree that in weird cases the best approach is to check with independent sensors. In my case it wasn't possible because of e-tuning. I feel lucky that the engine survived and the last 4 years runs strong.


Wishing good luck to Tor.

Since it's only happening between 3 and 4000 rpm, I suppose I could try and edit the A01G table in that area and less aggressively first and see if it has an effect.

I suppose a lighter flywheel would counter any dulling effect? My throwout bearing is making a lot of squeaking noises so a new clutch might be in a near future anyway.

In statistics, there is the saying "correlation does not imply causation".

Maybe the knock issue would have disappeared if you had used the carbon build-up chemical cleaner before getting rid of the tune. Or maybe it was a 3rd undiscovered reason you had knock.

Just saying that it is not really possible to know if you tune was actually to blame without having investigated more thoroughly.

Well the car was almost new and the problem appeared after using the tune and disappeared after I flashed back the stock definitions. I tried sometimes back and forth, but I had always problems. I am not saying that the tune was completely rubbish. There was an amazing improvement in fuel consumption. In fact the car had a 30-40% improvement, by working more time in closed loop! However, I wouldn't risk to lose my engine just for this reason.


In general I am a fan of what tuning can achieve, but only if it can be done by correct means. Check here an older post of what tuning improvements the GT86s had in the SP3 class category at the Nürburgring 24h race:


http://www.ft86club.com/forums/showp...3&postcount=13

That seems to be an unrealistic increase in fuel economy on the forrester. If your engine smelt hot id suspect it was running way lean for some reason, were you able to log afr and commanded afr and exhaust gass temp ( cat temp) overly high exhaust temps can jndicate lean condition.

If you still have tactrix you can log your 86. Is interesting excersise. Which rom calibration are you ? All you need to do is used sd mam card in tactrix and load the logcfg.txt and tactrix will intertogate ecu. ( No alterations just log )

Or just use toyota techstream software, free, with your tactrix to monitor 86

These were the fuel maps of the forester. I don't think it was something extreme:

Stock
http://i65.tinypic.com/3088o7p.png

Tuned
http://i63.tinypic.com/flwum9.png

The burning smell was in the middle range (1800 - 3200), where the tuned map adds a bit more fuel for knock resistance.


Anyway, I don't have the Tactrix cable anymore. So no more logging or changes for me :)

at low rpm cruising it probably wont be using the Open loop maps, it will likey be in closed loop. The closed loop tables are an offset from 14.7 and negative so if the closed loop tables contains -0.3 target is 14.4. If the def is bad or you put 0 or positive values in their then rearly weird stuff happens and it can run way lean and ltft is disabled and/or do other strange things.


mr throttle happy may have "hacked the 02 sensor scaling to fool ecu so he could run leaner cruise AFR than 14.7


see here


http://www.romraider.com/forum/viewt...p?f=15&t=11266


.

Was there anything you changed just before you started hearing this noise? or did it start right after a track day or something like that. Also I would like to know what oil you use.

Update:
I tried the MY17 transient table. I can't say anything for sure yet as I also removed 2 deg timing in the same area between 3 and 4k rpm due to some AVCS adjustments in the same range. The noise went away due to one or the other of these changes. Also, the throttle felt less responsive as Steve predicted, but not too bad.

After the AVCS adjustments didn't give the results I wanted (tried to adjust AFR with Intake cam - didn't work, or at least the few deg I adjusted didn't have any visible effect) I went back to my previous tables and restored the 2 deg timing as well. Since I didn't hear any noises I halved the values in the transient table and flashed again. The noise came back. Whether it was due to restoring the 2 deg timing or halving the transient values I don't know yet.

I wanted to flash the full MY17 transient again but started working on scaling my MAF instead (it was a productive day :) ). Will let you know how it works out with the full MY17 table and my normal timing.

Do you get throttle lag when doing this? Do rpms drop before it's revving up?
I once had this issue and solved it with increasing the corresponding values in my exhaust-avcs tables.
The cause was my own fault, I advanced the exhaust cams before for the while load range. Now they're back to stock (0-2k rpm, up to 0.7 load).

I find these threads terrifying cause you all seem so well versed in these graphs, charts and mechanical lingo, and I have NO idea what you're talking about. Oi vey, I have a lot to learn.

I did retard exhaust AVCS more at high loads in this rpm area. But I have been running that for months now without it making any noises and it doesn't look like it reaches those loads when revving with the clutch depressed. Also, when it makes the noise there is absolutely no lag, the response if very fast.

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

https://s2.postimg.org/l5mq08t4p/Scr...t_13.21.12.png

I drove the car to work yesterday and back home late a night where it was pretty cool (less than 15 deg). I still have the "half MY17" transients and tried a lot to provoke it, couldn't get it to make any noises.

It appears only to happen with higher IATs. I'm going to try the full MY17 corrections and see what happens.

I flashed the MY17 transient tables and I believe the sound went away.

I suppose there are too many variables to say what exactly caused the sound, if it was knock at all, and why I'm not hearing it anymore.

I also suppose there was a reason for Subaru to change the table and I feel more comfortable running more conservative values without any real disadvantages, so I'm going to stick with the changes.

Thanks for your inputs.

I have been running the 2017 TIR table on my B01C rom to avoid that damn knocking sound when blipping or when crisply getting back on the throttle after quick shifts. Well I just flashed the new OFT4 beta which uses the B01C TIR table so now I'm back to the damn knock sound. So last night I put the 2017 TIR table in the new OFT4 rom and now I'm back to the laggy blips but the knock sound is gone. So now I'm trying to blend the B01C table with the 2017 table for some sort of compromise. @Tor, I see you said you were going to look for a happy medium, did you ever make any progress with that?

Looks like the B01C table barely pulls any timing at all between 4000 and 5200 at any load. I'm guessing that is why blips are less laggy there but also produces the knock. So I was going to focus my effort there to start off. This is what I have so far (haven't flashed it yet though):
B01C left, 2017 Middle, Mine on the right
https://i.imgur.com/tC70DJy.png

It's a long time ago I messed with this. This is what I settled for:

https://s18.postimg.org/ue04vy7rd/Sc...t_17.10.04.png