Dominic Sorresso

recently, I ran into a situation where the compression ring on #7 cracked into 4 pieces. Fortunately, everything stayed in place. The LT5 is a pretty bullet proof motor and unbeknownst to me I was able to drive it like that for 2400miles. However, I did go through a significant amount of oil until I got home. We tore the motor down and redid the ring after checking the cylinder liners etc.
So I am a bit cautious regarding knock because that's the only thing I can point to as the cause of such a ring failure. In my tuning, I watch for knock. But it stumps me that knock appears at times when I am at a stable cruise with little to no change in throttle or vacuum. I have attached a part of a log which demonstrates knock retard. It appears to be within the 1800-2400rpm area and 55-70kPa. What I don't get is why knock would be induced with little to no additional load being put on the motor at the time it shows up.
Give the datalog a look. I will review the timing tables but of course more eyes are usually a better method of solving a problem.

1MeanZ

iTrader: (9)

I'm probably one of the least qualified persons to give a response to this...

Makes me wonder if you're on the threshold of what the sensor can pick up. In other words, it's detonating basically all the time, but the sensor only intermittently is able to pick it up. When it does it pulls timing and it goes away, then takes a bit for it to detect knock again. I don't know how sensitive the sensors are, or if detonation light enough to not set off the knock sensor is still harsh enough to break a compression ring.

Only other thing I could think of is that cylinder was way leaner than the others, but I'd think you would have been able to determine that when you tore it down.

Dominic Sorresso

Took car out again after having taken a bit of timing out in the areas that were exhibiting knock in previous datalog. I did quite a bit longer run this time and altho I did register knock, it wasn't the same total amount. So dropping some timing did help. However, when looking at the datalog, I saw the same evidence that I am getting knock with little to no throttle change. The one thing that does change is the MAP, and almost always its < 5%.
So I am wondering if I should simply bump the AE v Delta MAP table at <5%, or is there a scalar I should adjust instead? or both? I have attached a screenshot of TPRT w the scalars in the $D0A Mask pertaining to AE. I suspect the Delta MAP for AE scalar may need to be lowered because the changes to MAP are smaller than the 1.56% called for in the scalar.

I guess the one question I have is "why does this seem to be happening in the 1600-2400rpm range and between 50-70kPa?

Thoughts?

Vanilla Ice

It's the same reason you downshift to accelerate. You need more leverage.

KR is there for a multitude of reasons. Tuning it out completely is a waste of time because the variables contributing to it... vary. And what works when you're tuning may not be optimal later. It may also be worse. If it's not crazy leave it alone and rest easy knowing the ECU is doing it's job correctly.

I have a very hard time believing that this knock is damaging anything.

What gear and is there parts where you're uphill? I don't know what level KPA would be for your cruise gear.

If this was high throttle it would be different, but 18% throttle is no big deal at all.

Dominic Sorresso

As I noted, this is at a 6th gear cruise here in Illinois, so I am not climbing the Rockies. As u can see from the log, there is no accelerating or it is at a snail’s pace. In some spots, u can see that not even the TPS% value changes. The only thing I see changing is a very slight increase/decrease in MAP.

Dominic Sorresso

Am I looking at misfire?

Dominic Sorresso

I've continued to pursue this a bit more. It appears I may be on the right track by doing a couple of changes.

1. Dropping timing in small increments (no more than 1*) in what seems to be the area of greatest sensitivity

2. The only thing I can see from the logs is that small changes(<1kPa) to MAP can trigger knock counts altho TPS%, speed may not change. However, this is not consistently true. Its just that whenever I DO see knock counts, it appears when there is a minute change in MAP.

3. I have increased AE v Delta MAP pump shot in the 0-5kPa range

4. Finally, I have LOWERED the Min delta MAP for AE from 1.6kPa to .9kPa to target the MAP delta where the knock seems to be occurring.
So basically bigger pump shot at smaller increments of delta MAP.

Thoughts, comments?

84Elky

Dominic -- Take a look at the attached. Granted it's for $8d, but generally all GM masks deal with Knock Counts (KCs) in a similar manner. Fast knocks are accumulated when they occur and slow knocks are incremented when fast knocks reach 255. Most ADX's only report slow knock by default as yours appears to be doing.

If you can locate the address of the slow knocks being reported in your log (ALDL stream), you can probably safely change your ADX to add the fast knock. They will likely be the next 8 bit address. For example, if slow knocks currently being reported are in 0x00C1, fast knocks would be in 0x00C2.

Once you can report fast knocks, they may provide some additional info. If you can provide your mask ID, I'll see if can find a hack to get the actual address.

Also, I had a similar situation with a header slightly touching the frame.
HTH

Dominic Sorresso

This forum is always a wealth of info. I will say however that the KR shows up at the same time a KC is being reported otherwise no KR.

Vanilla Ice

This means the knock jumps up quickly in your case. Or at least while you're datalogging.

The Knock counts reported sounds like it's 2 bytes together. The MSB and LSB so a correct logging file would have both read.

RBob

iTrader: (1)

Pull the plugs too see if the reported knock is real?

It could be from the manual trans transferring drive-train noise to the engine...

RBob.

84Elky

I see that now. Just curious, what happens if you cruise steady at a MPH that creates approx. 50-55 MAP kPa as opposed to the 71-72 kPa in the posted log?

Dominic Sorresso

I may see a bit of knock showing up. But the rpm range is 1800-2400. Outside of that,no knock.

RBob,

Plugs show no indication of detonation. No pitting of plugs, no sign of porcelain w bits of metal.

RBob

iTrader: (1)

Look for bits of pepper flecks on the center porcelain.

RBob.

Dominic Sorresso

RBob

iTrader: (1)

Then it is most likely false knock. Can try another test to be sure, that is to put some higher octane fuel in the tank and see if the knock goes away.

If it doesn't then it is false knock.

If the knock does go away then it is real and just a trace of it at that.

RBob.

Dominic Sorresso

84Elky

This may be really stupid or a solution. Am approaching this from a retard perspective and not knocks despite what appears to be a correlation. There was a reason for asking about what happened if cruising at 50-55 kPa. Don't know anything about your code (it's $D0 isn't it?), but in $8D there is something called Low Octane Spark Retard. The default parameter is 70 kPa such that a sustained kPa in excess of 70 with minimal variance for an extended period (a couple of seconds) will cause continuous spark reduction. Your retard in the posted log was occurring at > 70 kPa fitting that condition.

It appears GM engineers in $8d and some other masks wanted to protect the engine under high sustained, and essentially unvarying loads.

Dominic Sorresso

Dominic Sorresso

Dominic Sorresso

Dominic Sorresso

RBob

iTrader: (1)

Yes, many ECMs have a forced knock test. Including $D0.

RBob.

Dominic Sorresso

RBob

iTrader: (1)

There is a status bit that shows when the ECM is in forced knock mode. Don't know if it is in the ALDL stream. Also, the SA will jump up, can sometimes see this as a staircase. Depends upon how much SA needs to be added to force knock.

RBob.

Dominic Sorresso

jeffas000073

Since I'm having the same issue, does anyone have an update on this?

Dominic Sorresso

Dominic Sorresso

Dominic Sorresso

Cold day today. Took a while to get coolant temps up high enough to enable LEARN. But I thought I would take it out since the sun was out. The ride helped me see what was going on w the knock counts. Turns out I could induce Knock and Retard by stabbing the throttle. Knock showed up both on the opening and closing of the throttle. I'm thinking I need to beef up the AE pumpshot. Other thoughts?

Dominic Sorresso

RBob

iTrader: (1)

Oil in the chamber will contribute to detonation. It has a very low octane rating and can easily ignite due to pressure and heat.

The engine may need some PCV system oil/vapor separators. Or even just a can to dampen PCV system pulses due to cam overlap. Had that problem before, the 108° LSA on a 224° at .050 duration cam pumped oil through the PCV system at an astounding rate. Added a can to dampen and the problem went away. And, very little oil collects in the can.

The issue I was solving was a lot of oil smoke. And the can eliminated it.

RBob.

RBob

iTrader: (1)

Additional info, the can used is an old carb type Holley fuel filter. Without the filter element installed, just some stainless steel scrubber in it. Can see it in this post:

https://www.thirdgen.org/forums/tbi/...ml#post4123039

RBob.

Dominic Sorresso

Dominic Sorresso