2015 ZL1 knock? Conclusion @ 4/27/15

[Nor Cal ZL1]

Originally Posted by jessrayo

I've been reading this thread off and on and wanted to make some comments.

First off in Oklahoma we have 91 octane E10 gas at the vast majority of stations. For the little time I drove my car stock on 91 I never noticed knock on pump gas. I have observed knock related to elevated IAT2 on several occasions. I can observe KR on my aeroforce gauges and if I look at the gauge when I hear and feel the knock I can see the digital confirmation of KR. There is no doubt in my mind you are hearing the knock... I hear it when it happens.

I think you have a problem that has not been identified or resolved. Because the car should not knock like that without beating on it. I have put my car on a road course at 100 degrees ambient and ran flat out till the paint on the brake calipers was smoking....and all the supercharger coolant had boiled out. Just hitting the throttle is nothing. I would contact Able Chevrolet and give them a run down of what has passed so far and see if they would be willing and able (pun intended) to bore scope it. Have them look for any sign of head gasket material in the bore. I kind of think changing the head gasket might fix your problem.

If the bore scope gets done and no problems are found I would take the car to a good tuner, add a pulley, headers, whatever else you want to do and tune it so it doesn't knock. I might even port the Heads just so you change out the Head gasket in case that is the problem and no one finds it.

As you said previously, that knocking will probably not affect GM over the life of their warranty but it will reduce the ability of the engine to handle more power in the future. So if they won't fix it I think it is in your best interest to fix it yourself. If you are going to fix the tune you might as well do a complete set of mods before you tune. There are many OK cars that make over 700 wph on 91 octane E10 gas and don't knock at all....and you can beat on them.

If you have a choice between 91 E10 or 91 pure gas, run the pure gas. As someone else pointed out above ethanol raises octane so 91 E10 is really about 87 gas with the ethanol blend...it is crap. But that is what I usually have to run in Oklahoma. Pure gas is more stable and it has more energy per gallon than ethanol.

My last point, in post #213 Z06 Bryan asked you about total ignition advance. It seemed like the answer you gave him was for knock retard. The engine is out of my Camaro again now so I can't look at what parameters you can see on the dashlogic but I think you can see total ignition advance, you may have to compare base spark and PCM spark adjust, I know you can see those two. Anyway, how much total advance you have at WOT is a factor here. That was Bryan's point. I know you are new on here but I have learned that Bryan is pretty darn sharp when it comes to anything concerning the tune in the car. Actually he has been on Camaro 5 longer than I have and doesn't post near as much as I do so if he takes the time to say anything about anything I would pay attention. I'm so radical I don't always agree with him but I've never seen him give bad advice. Good luck.

Okay one more point...if you decide not to tune you really should run torco...it has tested as the best octane booster and in generall it is as effective and cheaper than running race gas.

Im with Jess on this. I think a bit more digging into the issue is in order. My car has no knocking on 91. I would bet knock retard is taking place though. I would still follow up with a visit to Abel, and then to Starkweather. He is a rep for ADM, ADM built Jess's monster.

[angryBits]

Originally Posted by Nor Cal ZL1

Im with Jess on this. I think a bit more digging into the issue is in order. My car has no knocking on 91. I would bet knock retard is taking place though. I would still follow up with a visit to Abel, and then to Starkweather. He is a rep for ADM, ADM built Jess's monster.

I bet you are getting KR during WOT. Most of us are rarely WOT, so to hear the knock you'd have to be listening for it at that very moment and isolate the noise from valvetrain noise (which there is a lot of valvetrain noise in this car I've noticed!).

[Nor Cal ZL1]

Originally Posted by angryBits

I bet you are getting KR during WOT. Most of us are rarely WOT, so to hear the knock you'd have to be listening for it at that very moment and isolate the noise from valvetrain noise (which there is a lot of valvetrain noise in this car I've noticed!).

Could be possible but I don't hear any. I have been into performance cars and racing for 30 years including motor building and suspension setup, mainly for Italian cars, so I am a bit new to the American V8. I will listen closer next time I'm on it which is often. I would still investigate further to rule out issues and get a piece of mind. Ive lost ring landings in the past with Hemi designed Alfa motors from a little too much max advance, and leaned fuel mixture conditions, so if I heard the Z pinging or knocking I would have been all over it.

Ill take it out tomorrow and make a few wfo runs and see.
Wishing you the best with your Z.

[ZO6 Bryan]

Originally Posted by angryBits

Agreed on all points. Sorry to hear about your car troubles, but glad to hear someone can relate

Regarding Z06 Bryan, everyone seems to be defending him as though I've argued? I'm not sure why -- I don't think I've done any bashing or arguing (at least not intentionally). If it appeared that I did, I apologize. I'm a reasonable person and open to all good advice and can be persuaded away from my own ideas. However if my ideas still hold water, naturally I'm going to try them :P

I agreed with Z06 Bryan regarding the modification to the air intake -- he was right, that area is under vacuum and wouldn't work.

I semi-agreed about the Oil Separator. I think he's probably right, but its worth trying since its cheap and it wont hurt.

Regarding the tune -- it was really a matter of misunderstanding -- I think ultimately we agreed that it can be overwritten but GM won't do it.

That all seems fair to me, not sure why people are playing defense

I don't think they believe that you are bashing or being defensive, but that I given you advice on how to diagnose the problem, but you really haven't followed it. Forget the dealership and put a good scan tool on it and see exactly what's happening.
And Jess may be correct, if there is gasket material overhanging the bore it creates a hot spot that will cause pre-detonation.
And a good scan tool is EFI Live or HPTuners.
You can actually see Knock Learn in individual cylinders. So that can point you in the right direction. 1 cyl knocking a lot? Maybe a mechanical problem. All cylinders knocking? Probably a fuel problem.

[angryBits]

Originally Posted by ZO6 Bryan

I don't think they believe that you are bashing or being defensive, but that I given you advice on how to diagnose the problem, but you really haven't followed it. Forget the dealership and put a good scan tool on it and see exactly what's happening.
And Jess may be correct, if there is gasket material overhanging the bore it creates a hot spot that will cause pre-detonation.
And a good scan tool is EFI Live or HPTuners.
You can actually see Knock Learn in individual cylinders. So that can point you in the right direction. 1 cyl knocking a lot? Maybe a mechanical problem. All cylinders knocking? Probably a fuel problem.

Good advice, but that's step two.

Step one should be to take it to the dealer and see what they make of it, let them get the issue on file. So that's what I did.

Scan tool is $500 - $1000, dealership is free. Even if it doesn't pan out, anything free or cheap is worth trying.

[ZO6 Bryan]

Originally Posted by angryBits

Good advice, but that's step two.

Step one should be to take it to the dealer and see what they make of it, let them get the issue on file. So that's what I did.

Scan tool is $500 - $1000, dealership is free. Even if it doesn't pan out, anything free or cheap is worth trying.

You don't have to buy the software and cable. Find someone near you that knows what they are doing and has the scanning ability. The dealer should have done a snap shot of the problem with a Tech 2 and examined it the first trip. And if they can't examine it competently, send to GM to look at.

[angryBits]

Originally Posted by ZO6 Bryan

The dealer should have done a snap shot of the problem with a Tech 2 and examined it the first trip. And if they can't examine it competently, send to GM to look at.

This is what I was hoping would happen.

[Nor Cal ZL1]

Originally Posted by angryBits

This is what I was hoping would happen.

And would have if you took it to the right dealership, or as Brian has stated someone with the data logging capabilities. I have given you leads into perhaps the two best places to help you solve this in our area. I really like Brian's idea of logging each cylinder, that is a great suggestion.

[angryBits]

Originally Posted by Nor Cal ZL1

And would have if you took it to the right dealership, or as Brian has stated someone with the data logging capabilities. I have given you leads into perhaps the two best places to help you solve this in our area. I really like Brian's idea of logging each cylinder, that is a great suggestion.

Abel is a long way from me. I didn't see any harm in giving my local dealership a chance. Logging each cyl is next.

[angryBits]

*UPDATE*

Today w/ 3:1 mix of 100:91 respectively equating ~ 98 octane, I got KR but nothing I'm too worried about.

False KR twice
Car was about 1/2 operating temperature and I was totally easy with the throttle and got some false knock twice. Both while not in boost and low throttle. I'm sure it's false knock because it was a fairly high blip of KR (5deg) and then completely went away. I heard the noise and it was too solid to be an actual knock, so I disregard this. Similar thing happened later and I know it was false knock because I ran over some metal thing and it sent a KR to the computer as it hit something under my car, but I could hear it continue to bounce as it made its way to the rear of my car while I was driving.

So apparently this car likes to give false KR. Nothing wrong with that I suppose, just pointing it out so that others who are peeking at their KR like I am don't confuse the false KRs.

Real KR once
It was cold outside (for me thats about 50 degrees), I had 98 octane in the car and I was going uphill (increased load) plus WOT and I hit a KR of 2.1 for a moment. There was no audible knock and it was not repeatable. I believe this to be real KR as it climbed to 1.2 over about 1 sec and then it seemed to learn away even though I didn't let off the throttle. If a small knock occurs under these conditions, I'm not too worried about it. Though what happens when I lower the octane to 96 or 93...

Real vs False KR
Please correct me if I'm wrong, my believe is that an instant transition from 0 to X suggests a false knock. Where a climb from 0, then 0.2, then 0.5, then 1, ... X over a time period of 0.25-1s-ish (purely subjective) would suggest a real KR. Just my experience, yours may vary.

[Howdie_]

Thanks for taking the time to keep us updated. This is good info for all...

[angryBits]

Originally Posted by Howdie_

Thanks for taking the time to keep us updated. This is good info for all...

Thanks, I intend to keep logging my findings as I slowly lower the octane levels.

[ZO6 Bryan]

Originally Posted by angryBits

*UPDATE*

Today w/ 3:1 mix of 100:91 respectively equating ~ 98 octane, I got KR but nothing I'm too worried about.

False KR twice
Car was about 1/2 operating temperature and I was totally easy with the throttle and got some false knock twice. Both while not in boost and low throttle. I'm sure it's false knock because it was a fairly high blip of KR (5deg) and then completely went away. I heard the noise and it was too solid to be an actual knock, so I disregard this. Similar thing happened later and I know it was false knock because I ran over some metal thing and it sent a KR to the computer as it hit something under my car, but I could hear it continue to bounce as it made its way to the rear of my car while I was driving.

So apparently this car likes to give false KR. Nothing wrong with that I suppose, just pointing it out so that others who are peeking at their KR like I am don't confuse the false KRs.

Real KR once
It was cold outside (for me thats about 50 degrees), I had 98 octane in the car and I was going uphill (increased load) plus WOT and I hit a KR of 2.1 for a moment. There was no audible knock and it was not repeatable. I believe this to be real KR as it climbed to 1.2 over about 1 sec and then it seemed to learn away even though I didn't let off the throttle. If a small knock occurs under these conditions, I'm not too worried about it. Though what happens when I lower the octane to 96 or 93...

Real vs False KR
Please correct me if I'm wrong, my believe is that an instant transition from 0 to X suggests a false knock. Where a climb from 0, then 0.2, then 0.5, then 1, ... X over a time period of 0.25-1s-ish (purely subjective) would suggest a real KR. Just my experience, yours may vary.

A sudden spike of KR that then tapers off is exactly how real knock looks. Then a slow ramp up of KR that then tapers off is the PCM's attempt to keep it from knocking again.

[ZO6 Bryan]

Originally Posted by angryBits

Real vs False KR
Please correct me if I'm wrong, my believe is that an instant transition from 0 to X suggests a false knock.Real Knock Retard Where a climb from 0, then 0.2, then 0.5, then 1, ... X over a time period of 0.25-1s-ish (purely subjective) would suggest a real KR. preemptive knock retard Just my experience, yours may vary.

So you are likely still seeing real knock. What is you spark advance at WOT?