Help, I either need new engine or new knowledge!

[kwhiteside]

I've been tuning my track 2001 Z06 for a while now and have it to where it runs pretty well within what I thought I was supposed to be doing. The tune I inherited was knocking like crazy. I would drop the spark down each time I found knocking. I have ended up with a fairly safe tune that only has 19 degrees of advance when flying full throttle at high speed. The difference in speed and how hard the car pulls during a full throttle straight is greatly noticed from when I first inherited the car. Originally my high spark table was 25 degrees advance in the full throttle 100mph + ranges. Now I've subdued the knocking, but my car is much slower.

I've been researching a bit and have come to find that 25 degrees should be easy for my LS6 engine at full throttle. The 6 degrees I've lowered is giving up a ton of speed and the engine still knocks a bit. I'm thinking either something is mechanically wrong, or I'm ignorant about some tuning process.

I've attached a couple screen shots showing that when I get on it full throttle coming out of a turn, I sometimes trigger knock. Actual and Commanded AFR are pretty close. Sometimes .2 lean. The LTFtrims also concur that I'm pretty close as they are usually kicking in only 2-4% more gas.

One piece of info to consider is that my 01 LS6 suffers from the infamous ring flutter problem where the scraper ring allows some oil up into the chamber. I sometimes get black flagged for smoke upon decelleration coming out of a high speed straight because of this. I also have to keep adding oil (about 1.5 quarts over 2 days and 100 laps)

I've also recently ran some carbon buildup cleaner through my engine.

What causes knock? from my research, running lean, hot spots from carbon build up. How about burned up valves? Oil in the combustion?

Well, I don't seem to be running very lean if at all. My engine is old and I have already done the carbon cleaner (bg44 I think). I recently had my car compression checked and all cylinders were with 7 pounds of each other. Very consistent compression, so reason to believe my valves are ok.

All in all, I need to get the car pulling @ almost 25 degrees like they are supposed to and knock free.

Tune, Log, pics attached. Your help greatly appreciated. Don't worry about offending me. Just educate me and I'll take it humbly.

[joecar]

Other causes of knock (in addition to what you mentioned):
- lower octane fuel,
- hot intake air,
- oil ingested thru PCV system.

What gasoline are you using...?

When you ran top engine cleaner did you see the crap come out (infamous smoke cloud)...?
Did you let it soak for a while and then wring out the motor...?
If you have a borescope ($100 from most online tool houses) you can look inside each cylinder via spark plug hole... condition of piston tops may tell you something.

Have you tried setting your AFR to 12.6...? In some cases changing the AFR slightly may make a difference.

Other factors: condition of spark plugs, plug gap (GM revised gap from 0.060" down to 0.040"... my understanding is that this had mostly to do with misfires... but it may have some influence on knock when CC temps are high).

If you are seeing knock at WOT at the same RPM then there are several possibilities:
- if that is the peak torque (which it is not on the LS6), then CC temperature and pressure will be the highest (which promotes knock);
- it may be to mechanical noise and/or resonance that is being picked up by the knock sensors (valvetrain, bearings, piston rocking, mounts, exhaust/chassis interference)...

i.e. it may or may not be knock related, and it may or may not be engine related... the knock sensors are picking it up.

There's a tool called Chassis Ear which lets you remotely listen to any component of the car while driving (i.e. you clip the microphone clamp to the engine case, and you remotely listen from driverseat while driving)... this may also come in handy.

[kwhiteside]

Other causes of knock (in addition to what you mentioned):
- lower octane fuel,
- hot intake air,
- oil ingested thru PCV system.

What gasoline are you using...?

When you ran top engine cleaner did you see the crap come out (infamous smoke cloud)...?
Did you let it soak for a while and then wring out the motor...?
If you have a borescope ($100 from most online tool houses) you can look inside each cylinder via spark plug hole... condition of piston tops may tell you something.

Have you tried setting your AFR to 12.6...? In some cases changing the AFR slightly may make a difference.

Other factors: condition of spark plugs, plug gap (GM revised gap from 0.060" down to 0.040"... my understanding is that this had mostly to do with misfires... but it may have some influence on knock when CC temps are high).

If you are seeing knock at WOT at the same RPM then there are several possibilities:
- if that is the peak torque (which it is not on the LS6), then CC temperature and pressure will be the highest (which promotes knock);
- it may be to mechanical noise and/or resonance that is being picked up by the knock sensors (valvetrain, bearings, piston rocking, mounts, exhaust/chassis interference)...

i.e. it may or may not be knock related, and it may or may not be engine related... the knock sensors are picking it up.

There's a tool called Chassis Ear which lets you remotely listen to any component of the car while driving (i.e. you clip the microphone clamp to the engine case, and you remotely listen from driverseat while driving)... this may also come in handy.

I had a shop do the engine clean so don't know.

I will be changing the plugs soon and will get a boroscope to see.

When you say change timing to 12.6, do you mean in the PE table?

I'll look into the Chassis Ear thingy.

BTW, I'm not hearing any knock, and it doesn't happen every time. Some times it makes a pull knock free which confuses the heck out of me.

Ken . . .

[WeathermanShawn]

You look a little lean (AFR). As Joecar stated, I would slightly richen up you WOT to ~12.5-12.7 AFR. Your LTFT's at WOT are also indicating the need for a little more fuel.

I run a catch can. That helps a lot with carbon buildup. It is amazing how much oil that catch can can carry.

The only other thing that sticks out is your ECT at WOT. Your at ~ 207F. My thermostat runs at ~ 190-195F at WOT. I also have opened up the intake..the 'Free Ram Air' Mod.

My WOT Spark Advance is ~ 22-24 degrees, depending on how hot is is (IAT).

I would try the catch can, richen up your AFR at WOT, cool your ECT, etc.

[kwhiteside]

You look a little lean (AFR). As Joecar stated, I would slightly richen up you WOT to ~12.5-12.7 AFR. Your LTFT's at WOT are also indicating the need for a little more fuel.

I run a catch can. That helps a lot with carbon buildup. It is amazing how much oil that catch can can carry.

The only other thing that sticks out is your ECT at WOT. Your at ~ 207F. My thermostat runs at ~ 190-195F at WOT. I also have opened up the intake..the 'Free Ram Air' Mod.

My WOT Spark Advance is ~ 22-24 degrees, depending on how hot is is (IAT).

I would try the catch can, richen up your AFR at WOT, cool your ECT, etc.

I am curious to see your results. Good luck!

..WeathermanShawn..

I'm already running a catch can.

I have a Dewitts perfect fit Rad/EOC combo unit and it was only about 77degrees outside that day. I also have a Vararam Cold Air Intake system already. I have not altered my thermostat to a lower temp. Should I look into that?

I will richen up my PE table to 12.6.

Could you post up your tune or send me a copy just to compare?

These are some very real things I can attack. But as you see in my tune, I'm at 19.5 degrees WOT and still picking up some knock. In your experience, do you think richening up from 12.8 to 12.6 and dropping my ECT could make enough difference to put 3 degrees of advance timing back in?

[WeathermanShawn]

As a side note..I change tunes about 2 times a week, just to see how different parameters work. But, this has been a solid tune that has taken 1 1/2 Years to get it to my satisfaction. My current PE Table shows 12.8 AFR. but normally I will run ~12.6 - 12.7 AFR on the street.

And on this tune I have smoothed out the Spark Tables. Normally I will just run ~22 degrees at WOT, but this week I am trying something different.

I rarely get any knock, and even at this altitude..this car has some pretty good pickup.

Hope everything works out for you. Looks like you have a nice ride. You are free to try any portion of my tune.

[WeathermanShawn]

I do not know if iust lowering your ECT, or richening up your WOT will cure your knock problems.

I think it is a little unusual to have that amount of knock on a engine like yours. Do you hear it pinging or knocking? Mine makes a very distinctive pinging sound, that I can hear even over the exhaust sound. And when I lower the timing at that RPM and DYNCYLAIR the pinging sound goes away.

So, I trust my knock sensors. You might try desensitizing them or check that they are operating normally.

[kwhiteside]

Do you hear it pinging or knocking? Mine makes a very distinctive pinging sound, that I can hear even over the exhaust sound.

I have not heard knock in a while. I do know what it sounds like and have heard the detonation sound before when running lean on 100 degree days. Maybe the helmet prevents me from hearing it at the track, but I still have not heard it on my tuning runs where I get up to 110mph.

I read about the C6 having over sensitive knock sensors and some HPTuner guys talked about dulling them out, but I've not read about C5 guys having that problem, nor anybody on this forum under Type III LSX.

Ken . . .

[mr.prick]

Have you tried reducing {B6202} 25% from stock and
increasing {B6207} 50% from stock? :nixweiss:

[kwhiteside]

Have you tried reducing {B6202} 25% from stock and
increasing {B6207} 50% from stock? :nixweiss:

Ok, that makes sense on how to desensitize the knock sensor. Thanks.

Question is, should one do this. Sounds very dangerous to make the assumption the knock is false. If lots of people found this to be a recommended treatment, that might ease ones mind.

:help2:

[mr.prick]

Well, has this been a constant issue or a recent one?
What do your spark plugs look like?
Do you know if Ethanol is in the gas you buy?

[kwhiteside]

Well, has this been a constant issue or a recent one?
What do your spark plugs look like?
Do you know if Ethanol is in the gas you buy?

After started tuning after getting this car. I first logged it at road atlanta when high spark was flat line 25 and there was bad knock all over the place. As I've learned to tune, I drop the spark down to where I'm at now. Last week I went back to a track (Roebling Raod) where I know my car was much much faster down the straight and have concluded that my safe 19.5 degree timing causes the slower car. Yet I still have some knock as you see. Short answer, YES.

I would be very interesting to see if the knock happens on a dyno now that I have actual following commanded and the LTFTRIMS within -5 to 2 range.

Been a year since I've done the plugs. When they did the compression check they said they looked like new and didn't replace them even though I had a new set for them to use. I'll be looking at them again soon and if I go to the trouble of pulling them out, I replace them!

There is a slight chance I go to Road Atlanta this weekend. If I do, I would change the plugs, change PE to richer. These two things should have some effect. What about my ECT. Should I be tweaking my thermostat to get that temp down to the 190's.

I use 93 gas. Usually shell or chevron stations by the tracks. Quicktrip at home.

[mr.prick]

Looking at your log that KR is pretty high and
even tho LTFTs are positive during PE, AFR is a little lean.
IDC was about 90% BTW, bumping up fuel will make it higher.
If you can increase FP you might be able to lower IDC a little.
I have heard that certain crank pulleys can cause KR. :nixweiss:

You can drop the fan temps instead of changing the tstat.
I would:
richen PE AFR, lower the PE TPS% & turn of DFCO.
Kudos for using serial WBO2. :thumb_yello:

[WeathermanShawn]

Ken, if you look at my tune you will see a safe way to reduce the amount of KR, and how quickly it will decay.

I.E., instead of 4+ degrees of knock that last 15 seconds, you can safely lower it 25-50%, and make the KR go away quicker. It is a common technique. In effect you are not 'desensitizing' the Knock Sensors, you are just manipulating the tune to manage brief amounts of KR.

As long as you remember your settings, it is an acceptable way to manage KR. Obviously, you should pursue all the other suggestions.

[joecar]

Ken,

Most of your knock seem to be at about 4500 rpm (less than 5000 rpm)...

So try this (also): increase spark timing in the regions above 5000 or 5500 rpm... see 1st pic.

Also note: in the KR waveform when you see a "sawtooth" pattern (i.e. a spike followed by one or more spikes while the 1st/previous spike was decaying) then it most likely is real knock... see other pics.

Edited.

[kwhiteside]

Also note: in the KR waveform when you see a "sawtooth" pattern (i.e. a spike followed by one or more spikes while the 1st/previous spike was decaying) then it most likely is real knock... see other pics.

I do see a rise during the decay in the pic. Not a bunch and when I look through the whole log, 8 out of 10 just simply decay away. So tell me, those occasional teeth make you feel it is real knock?

[WeathermanShawn]

Ken, I usually get more worried about KR as I start hitting 100% Throttle. What is interesting about yours is that you are getting it a lot of times at values much less than WOT.

Are you sure nothing is banging around when you accelerate. Like a few others have noted, exhaust pipes and crank pulleys can make a metallic sound..and you get one big bang of KR, then nothing else.

I would say several portions of your log look like repeated KR due to the sawtooth nature, but a few you had one massive KR event, then even as you accelerated (and KR was decaying) you got none.

I still will stick with the following. If you can find 98 octane gas, fill it up with it and try your run. Or if you lower your timing and it goes away..probably KR.

I realize if you do that you will have little to no performance spark advance. Perhaps you have some false knock, with a little 'real' KR from time to time. Unfortunately, you might have to try those half-dozen techniques to eliminate the source.

[kwhiteside]

Looking at your log that KR is pretty high and
even tho LTFTs are positive during PE, AFR is a little lean.
IDC was about 90% BTW, bumping up fuel will make it higher.
If you can increase FP you might be able to lower IDC a little.
I have heard that certain crank pulleys can cause KR. :nixweiss:

You can drop the fan temps instead of changing the tstat.
I would:
richen PE AFR, lower the PE TPS% & turn of DFCO.
Kudos for using serial WBO2. :thumb_yello:

Fan level1 comes on at 190 and full fan at 195. This means my fans are on full force the whole time I'm at the track. From research, fans are irrelevent at the track, since you always going over 100 anyway, natural airflow is more then fan flow. My take on this piece of the equation is to get higher flow back to the radiator by using one or both of the Evans
180degree high flow thermostat
High Flow water pump
I'm thinking the thermo is a no brainer, but it wont happen by the weekend.

DFCO -- Why turn this off at the track? Are you just trying to keep more fuel in the system during decel, thinking that when I go full throttle I might avoid a lean spike (encouraging knock)? Keep in mind that road racing is different than drag strip. There is no dropping the hammer down EVER. Everything is smooth. When you slide through a turn exactly at the point where traction is about to give way, you cannot punch the gas. Guaranteed spin if you do that.

Injector Duty Cycle -- I see that when I knock, I'm around 60% and when at 140mph I'm at about 88% of my injectors. Now the way I understand this is that even though I'm not at 100%, the closer I get to that number, the better chance of some little fuel sputter which would cause a lean. When the knock happens however, 60% shouldn't be a problem should it?

BTW, thank you very much for working with me and taking the time to look at my tune. Prick, Joe, Shawn :grin:

[kwhiteside]

Ken,

Most of your knock seem to be at about 4500 rpm (less than 5000 rpm)...

So try this (also): increase spark timing in the regions above 5000 or 5000 rpm... see 1st pic.


I'm trying this, makes total sense. I see that happening too.

Just so you know where my mind is. When you come out of a turn you drop down to maybe 3k and need lots of torque to get up to the 5k range. It's very important. So important that if I cant resolve it, I will start throwing money at the engine. I have to fix it. Welcome to my obsession :doh2:

[mr.prick]

When my IDC got to 95% AFR was rich.

I turned off DFCO in CL because it made re-engaging
the clutch a little rough between gears. :nixweiss:

[kwhiteside]

Whats a day off good for. Working on your car.

I pulled my plugs, see attachment. All but one of them seemed overly white to me.

You tell me what you think.

Ken . . .

[joecar]

I do see a rise during the decay in the pic. Not a bunch and when I look through the whole log, 8 out of 10 just simply decay away. So tell me, those occasional teeth make you feel it is real knock?The only thing that can be said is this:
- sawtooth: this is very likely real knock (as KR decays, timing increases, knock re-occurs, repeatedly);
- single pulse: may or may not be a single occurrence of real knock.

e.g. if it really did knock, KR pulls timing which stops knock, then as KR decays timing goes back up which then allows knock again, this repeats several times or more... when you see a sawtooth pattern with say more than 3 or 4 peaks then this is what is happening;

if exhaust was banging on chassis: when engine goes to high load it leans in one direction against the motor mounts causing exhaust to bang once (maybe twice)... so going to WOT you may see a single (or maybe double) knock event as the engine initially enters high load;

you say you can't hear knock and that your spark plugs do not show any signs of overheating/knocking/detonation.

Diagnosis of knock is hard.

[joecar]

Do you have a closeup pic of that one plug...?

Is it just showing deposits due to octane adder...?

Does it have any metallic appearance on the ceramic tip...?

Does the ground strap look colored/discolored...?

[joecar]

...
BTW, thank you very much for working with me and taking the time to look at my tune. Prick, Joe, Shawn :grin:You are welcome, and I thank you for taking time to post... and I thank mr.prick and Shawn too, this is what makes the forum...:cheers:

Sometimes there isn't an easy answer... so just be persistent, someone will know something eventually.


Whats a day off good for. Working on your car.
...Isn't that the only reason to take days off...? :hihi:

[joecar]

Road racing is much harder on the car than drag racing...in DR you can "cheat" badly for a short time and get away with it, whereas RR is endurance-like and needs everything to be "exactly so".

I don't know how DFCO interacts with a manual transmission, but my thoughts were that maybe you want the extra fuel when you get back on the throttle, so you don't want to turn off DFCO... but I don't know.

[kwhiteside]

Do you have a closeup pic of that one plug...?

Is it just showing deposits due to octane adder...?

Does it have any metallic appearance on the ceramic tip...?

Does the ground strap look colored/discolored...?

I've tried 3 cameras and none of them take good closeups or I'm too stupid.

No spots on the insulator at all. Tips look normal. What ground strap are you speaking of?

[SOMhaveit]

Looks to me like knock retard occurs after an off throttle event and you leave PE mode, you have a commanded AFR of 14.1-14.6, I think. Then when you go back to an on throttle event after commanding an AFR close to stoic,you have a knock retard.

I would change B3616 to 20% for all RPM's while on the track.

I would get a cooler thermostat, 180 or 160, try Nook & Tranny, the thermostat & housing for the early LSx is about $40 delivered.

I would lower fan on temp for #1 to no more than 180.

I would look at plug heat range and consider a plug in a cooler range for the track. You are doing something most of us do not do, you are running sustained higher RPM's for sustained periods and because of that, you are achieving higher cylinder temps. Going to 14.1+ AFR on decel is just making matters worse.

I don't run a MAF tune, but it looks like you do. Your MAF curve is way different than the stock values for a 2001 Z06.

I had the same oil issues with my LS6 and the only solution is rebuild/replace. I tried everything I could think of or find, but once the oil is getting past the ring into the combustion chamber in large quantities, you're also going to get blow-by into the engine and that 2001 block you have doesn't have the capacity to equalize pressure the way the newer blocks can, so you get huge amounts of oil vapors pushed through the PCV system instead of being pulled by vacuum.

I put a simple pop off valve in my oil filler cap from McMaster-Carr that released upon any positive crank case pressure.

Good luck with it.

BTW, I'm far from expert, but these would be the steps I would take if I were in your shoes. So take it for what it is: one novice talking to another.

[joecar]

I've tried 3 cameras and none of them take good closeups or I'm too stupid.

No spots on the insulator at all. Tips look normal. What ground strap are you speaking of?Oh, I meant to say the ground electrode.

[joecar]

Try a colder plug as SOMhaveit suggested (e.g. NGK TR6 is colder than stock).

[5.7ute]

Try a colder plug as SOMhaveit suggested (e.g. NGK TR6 is colder than stock).

X3. I would also look at desensitizing the knock sensors as mr.prick stated.
I have come across this same issue with a 100,000 mi statesman I was tuning. No changes in spark, mixture etc would remove the knock in this same zone. After adjusting the knock sensors the KR disappeared completely, & subsequent checks with knock phones on the dyno & plug checks showed no signs of detonation.

[kwhiteside]

Thank you for that post SOMHavit. I never understood PE mode until meditating on your comments. I know see what it does and how we control when it kicks in as well as what it goes to.

1'st question. Sometimes it get knock exactly when PE kicks in. I'm cruising along at 45% throttle running 14.6AFR just fine, going maybe 85mph. Then I cross the 50% threshold and PE kicks in, the AFR goes from 14.6 to 12.75 and I spike a knock. Why does the knock not happen when I'm at 14.6, then when I throw gas at it knock starts? See PE1 attachment

My second attachment PE2_Backing, I'm in a high speed sweeper turn heading for the straight. Doing over 1G in that turn with the tires just barely holding the car on the track. You can hit that turn @ 110mph if you do it just perfect. I must have been crying for my mommy right there and backed off at 100mph before I went off track. This would have been a great time for some external noise to happen in my opinion. Just a thought. Hey, if you've already looked at my logs, take a look at this, it might bring it to life. http://www.vimeo.com/7767320

Most of the time when knock kicks in I'm between 3600 to 4500 rpm and my wideband reports that I'm .3 to .4 over what PE commanded has me at. Why am I over there and how do I get that corrected? All my tuning has been VE and MAF based, then my real driving hits this simple PE stuff, that I've really never messed with till now. See third attachment PE3, and notice my existing PE table and the proposed PE table on the far right. Aside from getting actaul to follow commanded properly, these changes should help.

I also have applied some of shawn's suggestions to the attack and decay rates of the Knock. See last two attachments KnockAttack and KnockRecovery. Basically attack less 25%, Recovery is amped up about 8 times from .012 to .100. Shawn has his at .250, I'm really not comfortable making a 8 times jump, much less Shawn's 20 times jump. But I see the logic of managing the knock by forcing the results to go away as fast as possible. I imagine if this change is not good, a true sawtooth will show up as the spark comes back in too fast.

Let me know what you guys thing.

Ken . . .

[kwhiteside]

Try a colder plug as SOMhaveit suggested (e.g. NGK TR6 is colder than stock).

I was going to start putting in my plugs tonight. I recognize those plugs as the Nitrous plugs :hihi:. Do you think Advanced Auto or AutoZone will carry those. If so, I'll go get some in morning and pop them in. As white as my plugs are, a colder plug should help. Of course we are also adjusting my PE to run richer which might take care of things without changing plugs. Any chance I might be overcompensating and lose some ponies in the process with the colder plug?

[kwhiteside]

Hey guys, I hope I'm not abusing you too much here. You have got me thinking about possible causes of knock. My car has always made a very loud clank at the track occasionally. If you watch the video above, it actually happened on all 3 laps. After the straight, there is a sweeping left (turn 3), then a pretty sharp right (turn 4). The clank happens in turn 4 each time after shifting the weight from once side, to the opposite. I have absolutely no clue what it is. My instructor didn't even notice it, but I know its there. I wouldn't even know where to start with a mechanic and this noise :help2:. Most would say, just ignore it. But since it might be very related to the subject at hand KNOCK, I ask your opinion of what it might be?

PS, sorry about the crappy sound in the video, I have two pieces of tape over the microphone to shield the wind noise. The engine sounds much much better in real life.

Ken . . .

[SOMhaveit]

Now you're asking questions above my pay grade.

I'll let someone like Joe who knows this stuff explain the cause and effect.

[joecar]

Some tools that may come in handy:

Relating to the clank noise (the non-wireless one is cheap):
http://www.ntxtools.com/network-tool-warehouse/JSP-6600.html
http://www.ntxtools.com/network-tool-warehouse/JSP-97202.html
You clip some of the mic's to different objects (e.g. engine case, motor mounts, suspension, k-member) and then you listen while driving.

This is cheap and lets you look at your piston crowns:
http://www.provision100.com/automotive_b.html
http://www.thetoolwarehouse.net/p-6275-provision-pv100.aspx

I want to get this: http://www.shopextech.com/p7573/extech_br250.php
The BR-250 is 9mm so it fits thru the spark plug hole; the BR-200 is 17mm so it will not.

Also, use a jewelers magnifier/lupe to closely examine the porcelain tips of the spark plugs, look to see if there are tiny metal fragments.

[joecar]

Remember, when load increases the PCM enables PE...

so it may appear that knock is coincident with PE enabling...

but consider the big picture: when you increase load, several things happen simultaneously:
- PCM computes a higher demanded load,
- PCM enables PE,
- combustion chamber temps starts going up,
- a throttle/airflow transient has just occurred, dynamic fueling (wall wetting/pooling/evaporation) has various effects on this (I'm a noob here);
- the engine tilts/twists against the motor mounts (something may hit),
- will the engine tilt/twist cause a weight transfer across the vehicle...?
- vehicle weight transfers rearward due to acceleration and to the outside due to corning,
- driveline (clutch/trans/differential) experience increase stress;

there's a lot going on in engine (thermodynamically, mechanically) and in the vehicle... motor mounts may make a noise, or suspension/chassis may make a noise...

then again, it might be something simple as spark plugs...

if your plugs are running that clean (like in the pic) then a slightly colder plug will be fine (it won't foul, it will run as clean).


I have heard of "rich knock" but I am told that you have to be overly rich (enough to wash down cylinder bores), and that in this condition the motor will be misfiring and/or wet fouling, and air/fuel charge will ignite in the header... (hmmm... I have seen some cars like this, the exhaust smell starts your eyes watering)... but I don't know enough about that topic.

[5.7ute]

Remember, when load increases the PCM enables PE...

so it may appear that knock is coincident with PE enabling...

but consider the big picture: when you increase load, several things happen simultaneously:
- PCM computes a higher demanded load,
- PCM enables PE,
- combustion chamber temps starts going up,
- a throttle/airflow transient has just occurred, dynamic fueling (wall wetting/pooling/evaporation) has various effects on this (I'm a noob here);
- the engine tilts/twists against the motor mounts (something may hit),
- will the engine tilt/twist cause a weight transfer across the vehicle...?
- vehicle weight transfers rearward due to acceleration and to the outside due to corning,
- driveline (clutch/trans/differential) experience increase stress;

there's a lot going on in engine (thermodynamically, mechanically) and in the vehicle... motor mounts may make a noise, or suspension/chassis may make a noise...

then again, it might be something simple as spark plugs...

if your plugs are running that clean (like in the pic) then a slightly colder plug will be fine (it won't foul, it will run as clean).


I have heard of "rich knock" but I am told that you have to be overly rich (enough to wash down cylinder bores), and that in this condition the motor will be misfiring and/or wet fouling, and air/fuel charge will ignite in the header... (hmmm... I have seen some cars like this, the exhaust smell starts your eyes watering)... but I don't know enough about that topic.

Good explanation Joe.

The logs appear to count out a tune related issue with the knock IMO. Either harmonics in the engine (valve train etc) or an external influence are triggering a false knock. Or there is a pre ignition event occuring due to hot spots in the cylinder, or plug strap etc.
I would be fitting a colder plug & logging again.

[Sid447]

Sorry for butting in here,

If this car is using "about 1.5 quarts over 2 days and 100 laps".
Then the engine is in a serious state IMO.

Also with the one plug being off-colour to the others, that you indicate as coming #7 seems to point to the problem.

Number 7 cylinder always runs hottest and is the most prone to detonation. Often failing or giving trouble in some way, usually by cracking or breaking the piston.

IMHO I'd have had the head pulled by now.

If what I think has happened has, then no amount of tuning will make a difference.

If that is the case, see below.

1. To avoid detonation problems in #7 fit the cylinder head steam pipes Part Number 12562169 "Pipe Bleeder" These were fitted to the early LS1 V8's only. The "fix" is a GMPP recommendation picked up from Katech when road racing.
If fitting this you will need to grind parts of the ribs on the underside of the LS6 intake to clear the pipe and allow the intake to fit.

2. Consider fitting forged pistons.

Apologies if I'm off-target and sounding like LS1Tech.

p.s. 207f or 97c for track work is pretty normal and re-doing fan speed settings or changing the stat won't make a bit of difference. A decent-sized stand-alone engine oil cooler positioned with a 1" airgap in front of the A-C condenser would though!

[WeathermanShawn]

Most of the time when knock kicks in I'm between 3600 to 4500 rpm and my wideband reports that I'm .3 to .4 over what PE commanded has me at. Why am I over there and how do I get that corrected?
Ken . . .

I would have to scan your tune again, but I assume your mainly running MAF. Between 3600-4500 Rpm's, those MAF Frequencies and the resulting airflow (g/s) {from your MAF Calibration Table} most likely need to be 'calibrated' upward ~2-3% to hit the AFR you are commanding in your PE Table. That will put you at your 12.7 AFR and most likely eliminate your +LTFT's.

Granted, my KR Recovery Rate is fairly aggressive. Since it is based on crankshaft revolutions, it sounds crazy at first glance. In reality, it keeps it under 1-2 seconds. Like you said, if it is real it will come back. But, it is smart to start slowly on those parameters.

A lot still sounds like you have a harmonic mimicking KR, but as Joecar said..KR is very difficult to diagnose. Especially if you really can not audibly hear it.

I take it your logs are from the track? Any chance of a 'normal' street run without any turns? It would be interesting to see.

I assume your fans are either going full blast or you have them disengaging at cruise. Again, I really doubt your ECT would be that sensitive to be knocking at that temperature, but it is a thought.

[kwhiteside]

I also posted a pic of my plug up on corvette forum and like Sid447, many are bothered by that one plug and state the same #7 cylinder fact.

This thread is option 1, trying to get some stable performance out of current setup for another season. Option 2 would be an LS6 crate.

For the poster above, you should know that this is the first year LS6 that suffered from ring flutter where the bottom scraper ring would allow oil up into the cylinder. There is a tech on it, they claim no performance hit and that the smoke is cosmetic. Some where actually able to get the rings upgraded under warranty. Mine is pretty old so I don't know if that is an option. I would argo the "no performance hit" theory by GM now that I now oil in the combustion area can alter the mixture enough to cause knock, therefore reducing timing, therefore reducing performance. I believe the oil consumption is due to this ring flutter. I usually puff some smoke when I decel after a high rpm straight. This is exactly the symptom descibed in the tech note. That puff often gets me black flagged which is very embarrassing to say the least.

Shawn, I'm a bit consused about your MAF comment. Looking at the track log I uploaded here, it seems I jump from 14.6 commanded right into PE mode. I'm not seeing MAF down to 12.8 like you suggest. Before PE mode I seem to be right on. Knock always seems to happen during PE mode.

I may be able to get a tuning run in this afternoon with the new tune. I doubt the temps will get nearly as high without track time though, and of course I wont be hitting much over 100 and only for a quick moment. Hard to emulate track time.

Thanks again for your help guys. I'll do what I can from the tune side, before jumping into the other options that require $$$. Mabye I could try playing the dealership games to see if they would fix the rings, but I don't have high hopes for that and hate the games.

TSB http://www.rjsmith.com/gm-894549.html
Article http://www.automobilemag.com/reviews/coupes/0207_chevrolet_corvette_z06/index.html

[mr.prick]

Don't be too concerned with the oil consumption, these motors are notorious for that
especially with the type of racing you are into.
Post up pics of the plugs.
IMO you are too lean for this type of racing, are you using race fuel?

[WeathermanShawn]

Overall, outside of a mechanical reason I agree with Mr. Prick that basically you are just too lean..With those hot ECT's/IAT's, cylinder pressures, racing, etc., just commanding ~12.5 AFR would usually cure most legitimate knock.

Ken, unless I have a few things backward..when in PE Mode your Commanded Fuel will be the richer of B3605 or B3618 when below 4000 Rpm's. Above 4000 Rpm's, B3618 dictates your Commanded Fuel. So, in PE Mode above 4000 Rpm's, if you are Commanding 12.7, but your wideband reads 13.0, your correction ultimately is applied directly to those corresponding MAF Frequencies found in Table B5001.

Granted a log off the track is not a true representation of your tuning challenge, but it might be a good 'control' run to compare.

[Mr. P.]

Sorry for butting in here,

If this car is using "about 1.5 quarts over 2 days and 100 laps".
Then the engine is in a serious state IMO...
:iamwithstupid: I know that I'm a little late to this thread, but I have to agree completely this motor sounds like it is under duress. When your oil control issues are bad enough that you are being black-flagged it's a problem.

kwhiteside - what is your PCV system like? is it still stock? If so I would HIGHLY encourage you change that as follows:
1) install a catch-can in the line from the PCV valve to the intake manifold
2) install a vented oil-fill breather/cap (like this one http://www.summitracing.com/parts/CEI-103032/)
3) permanently remove the stock fresh-air PVC hose from the motor (the hose from the throttle-body to the valve cover) and cap off both bungs with 3/8" vacuum caps

Assuming you use a quality catch-can, this will *absoutely* prevent oiling into the intake via the PCV circuit on a naturally aspirated motor.

Following this, if you see visible oil consumption as you let off the throttle (high manifold vacuum) then you are pulling oil down the intake valve stem seals, they need to be replaced; this is common on high-mileage motors.

If you see visible oil consumption as the RPM goes up, that is ring-flutter.

Get your oil consumption under control, inhaling that crap makes the fuel octane nosedive not to mention on a competition car being a quart low will work the hell out of the oil still left in the pan plus you risk the oil pump gulping air in an extended high-G maneuver.

My 2-cents.

Mr. P. :)

[kwhiteside]

:iamwithstupid: I know that I'm a little late to this thread, but I have to agree completely this motor sounds like it is under duress. When your oil control issues are bad enough that you are being black-flagged it's a problem.

kwhiteside - what is your PCV system like? is it still stock? If so I would HIGHLY encourage you change that as follows:
1) install a catch-can in the line from the PCV valve to the intake manifold
2) install a vented oil-fill breather/cap (like this one http://www.summitracing.com/parts/CEI-103032/)
3) permanently remove the stock fresh-air PVC hose from the motor (the hose from the throttle-body to the valve cover) and cap off both bungs with 3/8" vacuum caps

Assuming you use a quality catch-can, this will *absoutely* prevent oiling into the intake via the PCV circuit on a naturally aspirated motor.

Following this, if you see visible oil consumption as you let off the throttle (high manifold vacuum) then you are pulling oil down the intake valve stem seals, they need to be replaced; this is common on high-mileage motors.

If you see visible oil consumption as the RPM goes up, that is ring-flutter.

Get your oil consumption under control, inhaling that crap makes the fuel octane nosedive not to mention on a competition car being a quart low will work the hell out of the oil still left in the pan plus you risk the oil pump gulping air in an extended high-G maneuver.

My 2-cents.

Mr. P. :)

I'm running exactly what you describe already.

[kwhiteside]

So, in PE Mode above 4000 Rpm's, if you are Commanding 12.7, but your wideband reads 13.0, your correction ultimately is applied directly to those corresponding MAF Frequencies found in Table B5001.

1'st read, did not compute in my brain. So I'm .3 lean in PE mode, how does B5001MAF factor in?

Ok, so I did a log run a little while ago. New TR6 colder plugs gapped .040. I did NOT flash the new tune we've worked up. Wanted to see how the plugs and straight line stuff affected. Not good. See the attached log. Still lots of knock (again, same tune as at track still). Temps did get similar to track time as I drove the car around for 40 min before doing a log run. Unless any further suggestions, I suppose flashing the tune is next step.

[WeathermanShawn]

Ken, I usually plot my LTFT's and PE AFR Error using Table B5001. I use a MAP that shows what MAF Frequencies correlate to what AFR. I adjust it accordingly. But, there are many ways to do it.

However, I agree that is too much KR to operate your engine. Your AFR's looked fine, but basically my conclusion would be that either pre-ignition, detonation or a massive valve-train harmonics is contributing.

While the initial KR looks 'false' in that is so abrupt and massive, it does repeat and seems to occur around the same RPM range.

Does the car seem slower?

[joecar]

SS,

Hey bro, you're not butting in, your comments are welcome...:rockon:

Yes, cyl #7 is known to run hotter, I was hoping to see a close up picture of #7 plug.

Good point about the rear steam vents being blocked off from the factory... if Ken doesn't like to grind off the structural stability ribs on the underside of the manifold, then he could instead install a front crossover steam pipe at the rear, and plumb it to the front using a T fitting and some heavy duty hose.

Hmmm... if he's RR'ing then an engine oil cooler may be a good idea in general.


Sorry for butting in here,

If this car is using "about 1.5 quarts over 2 days and 100 laps".
Then the engine is in a serious state IMO.

Also with the one plug being off-colour to the others, that you indicate as coming #7 seems to point to the problem.

Number 7 cylinder always runs hottest and is the most prone to detonation. Often failing or giving trouble in some way, usually by cracking or breaking the piston.

IMHO I'd have had the head pulled by now.

If what I think has happened has, then no amount of tuning will make a difference.

If that is the case, see below.

1. To avoid detonation problems in #7 fit the cylinder head steam pipes Part Number 12562169 "Pipe Bleeder" These were fitted to the early LS1 V8's only. The "fix" is a GMPP recommendation picked up from Katech when road racing.
If fitting this you will need to grind parts of the ribs on the underside of the LS6 intake to clear the pipe and allow the intake to fit.

2. Consider fitting forged pistons.

Apologies if I'm off-target and sounding like LS1Tech.

p.s. 207f or 97c for track work is pretty normal and re-doing fan speed settings or changing the stat won't make a bit of difference. A decent-sized stand-alone engine oil cooler positioned with a 1" airgap in front of the A-C condenser would though!

[kwhiteside]

I just couldn't help myself guys. I flashed the tune and went for another run. I'm very surprised what a difference it made. My new tune and recent log attached.

I could go a little richer on PE if necessary. Any other suggestions welcome. Of course the goal is to get my timing back up to 22 degrees area.

[kwhiteside]

Ken, I usually plot my LTFT's and PE AFR Error using Table B5001. I use a MAP that shows what MAF Frequencies correlate to what AFR. I adjust it accordingly. But, there are many ways to do it...WeathermanShawn..

Hey Shawn, walk me thru that map please. I have a LTFT Ben and LTFT Avg that I got from Mr. Prick already in my logs.

Data?
Column?
Row?
paste row values from b3618 I assume.

Thanks in advance.

[kwhiteside]

SS,

Hey bro, you're not butting in, your comments are welcome...:rockon:

Yes, cyl #7 is known to run hotter, I was hoping to see a close up picture of #7 plug.

Good point about the rear steam vents being blocked off from the factory... if Ken doesn't like to grind off the structural stability ribs on the underside of the manifold, then he could instead install a front crossover steam pipe at the rear, and plumb it to the front using a T fitting and some heavy duty hose.

Hmmm... if he's RR'ing then an engine oil cooler may be a good idea in general.

I'm running a FAST92 Intake so I'm not sure if those ribs exist?

I'm running a Dewitts Rad/EOC combo unit. Now those plugs were in for many days of hotlanta tracking before I got the EOC. Oil temp was up to 295 before the EOC :Throwup: , since then it runs stable around 245 degrees in the scorching sun.

[mr.prick]

Did you just lower the knock rate?
LOL there is a lot less KR now.
I was wondering if the KR sensors were bad.
That #7 plug is discolored because of how lean you were running overall.
#7 is know to be leaner than the rest,
it tends to be the one that gets BBQ'd.
If you have the stock pistons still be thankful #7 didn't disintegrate.

On a side note I feel that tracking {B5913}/{B5914} with
DYNCYLAIR_DMA is better than using DYNCYLAIR or CALC_CYLAIR.

[kwhiteside]

Hope this is good enough

[joecar]

...
Ken, unless I have a few things backward..when in PE Mode your Commanded Fuel will be the richer of B3605 or B3618 when below 4000 Rpm's. Above 4000 Rpm's, B3618 dictates your Commanded Fuel.
...My understanding is that the PCM uses the richest AFR (or EQ) from all tables that are currently active...

i.e. when PE is enabled, then the richer of B3605 or B3618 regardless of 4000 rpm.

Is the 4000 rpm from B0120...? B0120 sets the thresold between MAF/VE or MAF only operation for calculating cylinder airmass, and is not related to commanded AFR.

:)

[kwhiteside]

Did you just lower the knock rate?


25% lower knock sensitivity
8 times faster recovery

PE Richer

Timing actually bumped up after 4800, but I never got there on the streets. I don't stay at 100mph but for a second or two during tuning sessions. Paranoia you know.

TR6 plugs

[joecar]

The ring flutter problem is causing large oil consumption and this is a problem (oil entering CC via rings) in that it lowers the effective octane and causes burnt oil/carbon deposits which glow when hot (which may increase CR a little) all of which promotes preingnition/detonation.

[joecar]

I'm running a FAST92 Intake so I'm not sure if those ribs exist?

...I don't think the FAST allows the early LS1 steam pipe system...

You might consider installing a steam crossover tube at the rear and plumbing it to the front corssover tube (which exits to radiator neck).

[WeathermanShawn]

Ken:

I take my LTFT's as indicated. I then adjust Table B5001 by the same percentages.

Wherever I have 0.0 LTFT's, I know I am in PE Mode. I then filter (WOT) the following MAP(s) to determine what frequencies I am in PE Mode. So, if I am off by .3 AFR..that is about 1%. I.E., my PE AFR Error is usually within 1-2%, so the I am simply 'eye-balling' my logged WOT AFR against my MAF Frequency in PE Mode.

[joecar]

#7 plug looks good, looks like it's cleaning itself... I can see oil on the inside of the steel shank... is that what I see...?

[kwhiteside]

My understanding is that the PCM uses the richest AFR (or EQ) from all tables that are currently active...

i.e. when PE is enabled, then the richer of B3605 or B3618 regardless of 4000 rpm.

Is the 4000 rpm from B0120...? B0120 sets the thresold between MAF/VE or MAF only operation for calculating cylinder airmass, and is not related to commanded AFR.

:)

So you're saying if I hit the PE rpm/throttle position threshold and even if I'm at 3600rpm, it will drop down to 12.65 as stated in the PE table. That is what I'm seeing.

I still would like to know how to tune when PE is hitting the commanded vs actual.

As for my actaul sometimes being a bit higher then commanded when in PE mode, please not that I'm running a LS2 90mm TB instead of my stock 78mm. Mabye my multiplier isn't perfect. From the tuning process MAF should be very very close, but PE table has never been tuned at all, as I don't have a clue how to do that.

[joecar]

I just couldn't help myself guys. I flashed the tune and went for another run. I'm very surprised what a difference it made. My new tune and recent log attached.

I could go a little richer on PE if necessary. Any other suggestions welcome. Of course the goal is to get my timing back up to 22 degrees area.Ok, big difference... what did you do...?

Yes, go a little richer as suggested above.

[WeathermanShawn]

My understanding is that the PCM uses the richest AFR (or EQ) from all tables that are currently active...

i.e. when PE is enabled, then the richer of B3605 or B3618 regardless of 4000 rpm.

Is the 4000 rpm from B0120...? B0120 sets the thresold between MAF/VE or MAF only operation for calculating cylinder airmass, and is not related to commanded AFR.

:)

Thanks Joecar..

I knew I was close, but now I get it.:)

[kwhiteside]

Ok, big difference... what did you do...?

Yes, go a little richer as suggested above.

see post #54, if you want the detail, I posted screenshots comparing old and new values even higher up the thread, and of course the end tune was just posted up.

If you see anything scary, please feel free to say so.

Ken . . .

[curtbriggs]

[QUOTE=kwhiteside;109540
My car has always made a very loud clank at the track occasionally. If you watch the video above, it actually happened on all 3 laps. After the straight, there is a sweeping left (turn 3), then a pretty sharp right (turn 4). The clank happens in turn 4 each time after shifting the weight from once side, to the opposite.

The Clank: Check and Lube the axle splines where they slide into the hubs. The corvetteforum.com has info on the fix.

Oil Burn: my 55,000 mile engine burns One Quart of MobileOne 5W30 per 1000 miles. RedLine 5W30 is 1/2 that. Amzoil 0W5 at the end of a 2500 mile trip was zero, I couldn't read it on the dip stick. I hate paying the price for Amzoil, I did the dealer thing just for my own use and after paying the fee, it might be cheaper to get from someone else. I can say that so far, I'm impressed.

You can't trust what you read on the web but my comments are based on 1000 mile one day interstate trips and WFO everytime I leave a rest stop. At my age, lots of rest stops. I rev it to 6000 when I'm just playing.

I have a catch can and it's always dry. I did one DE at VIR on RedLine with track temperatures of 120* and used one quart for the day. I filled to 1 qt above the full line.

With the know ring problem, maybe a change to a different oil may help reduce some of your oil consumption.

Cheers, Curt

[kwhiteside]

The Clank: Check and Lube the axle splines where they slide into the hubs. The corvetteforum.com has info on the fix.


Curt, you may have nailed it. I've been leaking some grease onto the inside of my rims from my axle seals this season and plan on replacing the whole axle shafts/seals this winter. I never imagined that could be the clank. Man that would be great if that makes the clank go away!



Oil Burn: my 55,000 mile engine burns One Quart of MobileOne 5W30 per 1000 miles. RedLine 5W30 is 1/2 that. Amzoil 0W5 at the end of a 2500 mile trip was zero, I couldn't read it on the dip stick. I hate paying the price for Amzoil, I did the dealer thing just for my own use and after paying the fee, it might be cheaper to get from someone else. I can say that so far, I'm impressed.

I've played a lot with oils. You might have guessed that a guy with oil problems would explore that. Started with Amsoil 5W30 last year. This year I did some research and switch for the hot months to Mobile 15w50 race oil with the most lead of any oil manufactured. I actually did a whole weekend at Road Atlanta in 95f temps and only used 1 quart the whole time. I decided with winter comeing and the weather a bit cooler for Roebling Roag to try the Racing Amsoil 10w40 with lead added. That is the oil I just used and as I stated, it burned up quite a bit of it.

I'll be going back to the Mobile 15w50 in the spring. You can read lots and lots of stuff, but I've got an oil using engine and my real world experience says this stuff is the best for my engine. You might give it a try. Easy to find and any parts store.

[curtbriggs]

[QUOTE=kwhiteside;109763] the most lead of any oil manufactured. I actually did a whole weekend at Road Atlanta in 95f temps and only used 1 quart the whole time. I decided with winter comeing and the weather a bit cooler for Roebling Roag to try the Racing Amsoil 10w40 with lead added.

With roller lifters and semi-roller stock rockers, I don't see the need for the Lead additive in your oil choice. Lead is great to prevent lifter scuffing in flat tappet motors. Hard on Cat converter life is why they have reduced it.

While your cylinder walls are still in good shape, you might give some thought to re-ringing the motor and adding ARP rod bolts and maybe forged pistons. When the heads are off, that's the time to look at the lifters and ??????????? One thing leads to another.

I hope you have a magnetic plug in your sump. I pulled my rocker arm cover to install a set of Yellow Terra roller rockers and found one stock rocker lost all the needles on one side. The side retainer had popped out. Found two needles on top of the opposite head. The mag plug got all the rest. No noises to clue the problem.

Good Luck, Curt