Pros - Need help understanding Knock/KR - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 02-25-2007, 03:05 AM   #1
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Default Pros - Need help understanding Knock/KR

First, I have an AutoTap. I've had ongoing "issues" with what AutoTap reports as "Knock Counts", and low to mild KR under mild load, going uphill, or cruising while the TCC is locked. Sometimes the KR can hit 7 to 9 .

I understand knock is predetonation. I've been told different things, for instance, you should never see any KR being applied. Up until lately, it was my understanding that what the AutoTap picks up as "Knock Counts" are actual counts of what it is detecting as a knock, so it then applies KR.

Going under this assumption, I've been trying to elliminate the KR. No luck. I'm no expert, I have a friend that is somewhat of one. He borrowed a Tech II from work-- readings looked like what my AutoTap said, so at least the AutoTap is acurate to some level.

Now, I don't know what knocking sounds like. So I've been told this might be false knock, and if so, don't worry about it. I think I understand what false knock is, but I don't know if what I am seeing is false knock.

Frustrated, I took my car to a dealer, I've been to everybody else.

Making a long story shorter, in the end nothing happened, other then flashing the PCM, and doing a CASE learn by somebody else.

Being one of the "best techs" there, especially with 3800s, I guess, he tried to explain to me what was happening. I'm not sure yet if it makes sense, but again, hoping some pro in here can help me out:

1) KR is normal
2) KR is a "part" of the computer'* attempt to keep fuel economy
3) The "Knock Counts" Counter is not actually a definitive measurement of knock occuring in the engine. I'm not sure whether he said either that it was a measurement by the computer as to gauge when to apply KR, or how many times it has applied KR, but it was something like that.
4) You actually want to see KR/KR Counts because the computer is adjusting timing "appropriately"

He said I should only really be concerned if the KR was more constant, around like 7 degrees or higher. It typically does not go higher then 3 or 4.
But can hit 7 or higher

Some facts:

Fuel Ratio is 14.7 x 1, sometimes 13.6 x 1 or something
Timing can range from -26 to -37 (don't know if that is normal)
LTFT does typically stay rather high, around 8-10 +, which I understand as meaning the engine is running more lean- he didn't say much about that. LTFT tends to have no pattern whatso ever, other then hanging at a certain level, yet fluctuating, never really below 0.

I've been told tthe 2nd O2 sensor doesn't really matter, so then the LTFT doesn't matter- I don't understand that.

STFT comes and goes within 10 degree back and forth of 0, though usually uneven and hangs more like between +3 to -7

I guess what I'm really asking is- is what I am seeing normal, for an engine with 40-50k on it (maintained), stock except just a K&N cone filter. The car itself has 140k on it, and has also just had a trans rebuilt. But I'll stop there.

Is this all normal stuff, and the explanations of what those things mean correct? If not, umm, help...? I just want to make sure I'm not seeing signs of something that might lead to damaging something down the road.

Thanks in advance
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Old 02-25-2007, 09:37 AM   #2
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You might expect to see the computer retard the spark under heavy load while accelerating to compensate for the octane rating of the fuel you are using, but even that should just be a few degrees. It does this using the knock sensor(*) which acts like a microphone to listen for the clattering or knocking noise caused by pre-ignition or detonation. When the knock sensor picks up these sounds, the computer reacts by retarding the spark in an attempt to eliminate the detonation.

The knock counts are just that, a numerical summation of knocking sounds picked up by the knock sensors. Full spark advance can only be achieved at 0 knock counts.

I think of KR as Knock Retard or the degree of timing that is pulled or removed from the engine. So, if you are running at 17 degrees BTDC, and the engine begins to knock, you might see the computer retard the spark to 13 degrees BTDC, for example.

If you are picking up a continuous knock count, it is most likely false knock caused by a lifter or other mechanical component. If you disconnect the knock sensors, a code will be set, turning on the CEL, and the timing will be continuously retarded by 10 degrees by default. With a continuous mechanical knock, the computer can pull as much as 15 degrees of timing. This allows the car to accelerate at about the speed of melting snow.

Hopefully, others will chime in to correct me or to help with more specific info.
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Old 02-25-2007, 11:35 AM   #3
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First of all, KR isn't 'normal'. Assuming you're running premium fuel as you should, a bone-stock L67 should have no KR under normal conditions.

1-2 degrees is acceptable at times, but 7 is what I'd call extreme.

Secondly, is your cone filter exposed? This is hurting you by pulling in pre-heated air from the engine compartment. I suggest going back to the stock airbox for the time being until you get this problem solved.

You swapped in an '02 L67. Which TB and MAF sensor are you using?
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Old 02-25-2007, 07:01 PM   #4
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bill-

Define what you mean by picking up continuous knock counts?

At say, 45-55mph, in overdrive, crusing, you will see a steady stream
of knock counts- like a timer. KR during these times varies, but typically does not
hit or stay at zero. Most of the time it stays around 3 to 5 degrees.

Othertimes, a knock count registers occasionally, or a few at a time, especially at slower speeds (lower gears). A count will not register by any physical "hit" to the car, (pot holes, train tracks, etc). The counts are not related to occasional misfire I get, at slower speeds. Random cylinders. Nothing in the computer'* history counters for misfire.

willwren

I thought L67 was */c? L36 is N/A I thought, mine isn't supercharged.
it'* cold outside, so at this time at least, I don't think it'* pulling in that much hot air from the engine! And unfortunately, I threw out the stock airbox ages ago. I actually would buy one from somebody in here, just to put back on, to rule the filter out of the equation.

the original MAF/TB are on this motor.I can't remember what it was, maybe it was something stupid like vacuum lines, but at the time, I was told the 02 TB couldn't be used, because the vacuum lines were different or something, and they couldn't attach something to something, or there wasn't a line for something... I dunno. I have the 02 TB/MAF, and would throw it on, incase that made a difference, but I do see the vacuum lines are different. I'm not sure if something should be connected differently.

Although that doesn't make much sense to me anyways, since the engine came "whole", unless it didn't include something like the evap purge valve, what wouldn't be able to hook up to what?

PS - If anybody knows anybody with a stock airbox for a reasonable price, send them my way...

Thanks
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Old 02-25-2007, 09:01 PM   #5
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Quote:
Originally Posted by Daron97SSE
bill-

Define what you mean by picking up continuous knock counts?

At say, 45-55mph, in overdrive, crusing, you will see a steady stream
of knock counts- like a timer. KR during these times varies, but typically does not
hit or stay at zero. Most of the time it stays around 3 to 5 degrees.

Othertimes, a knock count registers occasionally, or a few at a time, especially at slower speeds (lower gears). A count will not register by any physical "hit" to the car, (pot holes, train tracks, etc). The counts are not related to occasional misfire I get, at slower speeds. Random cylinders. Nothing in the computer'* history counters for misfire.
By continuous counts, I was referring to what you get when you have a mechanical problem. On my '95, I had a valve train tick that I could not find. Well, let'* say I was not willing to replace the entire valve train to get rid of it. When I put my scan tool on the car, the knock counts continuously increased, and the PCM pulled timing. This happened at idle, at cruise, during acceleration, all the time, because I had a continuous noise. The sensors were just doing what they were supposed to. However, the car would not run worth a dam. I knew the noise was valve train, and nothing serious, so I disconnected my knock sensors. My car ran BETTER with the default 10 degrees of retard, but was still pretty awful. I then installed resistance loads equivalent to a knock sensor hearing nothing, IIRC, about 3.5 Kohms each to the knock sensor leads. Voila, I had one hot L36. 0 knock counts, 0 KR. Always. I don't recommend that others do this, as the knock sensors prevent engine damage that can be caused by frequent detonation. But, it has been two years and about 20,000 miles, and I only hear light detonation when the engine loads up under acceleration - like on an uphill on-ramp before a downshift. Before knock sensors, this was considered normal and acceptable, and it still seems that way to me. I run 89 octane gas and am happy with my little spoof setup.

You say you will not pick up a knock count from road noise, but have you checked the function of the sensors by hooking up the scan tool and tapping on the engine block? If that doesn't show as knock counts, you have a bad sensor. If you do have to change one, they are a little tricky to install. They are installed in the coolant drain plug holes and must have sealant on the threads, but not on the first few. That'* because the ground connection to the block is made through the threads and they need good metal to metal contact. The installation torque for them is pretty low too, IIRC, about 11 or 12 ft-lb.
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Old 02-26-2007, 12:27 AM   #6
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Well, how about this--

Took some pictures of the spark plugs I yanked the other day from my car. Now, when the engine was swapped in, the guy told me that he looked at the plugs, and they were good. If that is true, then what happened to these... To me, a couple of plugs look like they show signs of long term predetonation. I don't have the terminology, but the metal bar that bends up and over the electrode, I believe, looks "bent" on some of them. Other then covered in carbon, they were dry- no coolant, no oil. Do they show anything?

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Old 02-26-2007, 01:43 AM   #7
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Looks like someone tried to gap them by bending the side electrode. And the gap looks kinda big. What does it measure? Consider a set of NGK TR-55 plugs. They work very well and have a great reputation here on BC for both our L36 as well as the L67. I run them with premium Belden wires and have been very happy.
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Old 02-26-2007, 02:55 PM   #8
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do they show any signs of... knocking or something?

Also, tested tapping the block, and looking for knock counts.

Although it does have to be more then a tap, you will get knock counts by hitting the block- this is with the motor running if that matters.

I might hear some chatter at idle, but knock counts never register there.

Something else odd- AutoTap shows the EVAP System test as incomplete.
been like that for a while- my gas mileage has gone threw the floor too!

yikes, too many symptoms!
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Old 02-26-2007, 03:33 PM   #9
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Quote:
Originally Posted by Daron97SSE
do they show any signs of... knocking or something?
Not that I can tell from the photos. Severe detonation can break the porcelain, or worse. Yours appear to me to be improperly gapped.

Quote:
Originally Posted by Daron97SSE
Also, tested tapping the block, and looking for knock counts.

Although it does have to be more then a tap, you will get knock counts by hitting the block- this is with the motor running if that matters.

I might hear some chatter at idle, but knock counts never register there.
Those results indicate normal functioning of the knock sensors, and that you do not have a continuous mechanical problem, like I had. Do you hear any engine noise when you see the knock counts increasing?

Quote:
Originally Posted by Daron97SSE
Something else odd- AutoTap shows the EVAP System test as incomplete.
been like that for a while- my gas mileage has gone threw the floor too!

yikes, too many symptoms!
Lots of things can be contributing to your problems. It seems to me like you might start with the simple stuff first that should be done on any engine, like new plugs and wires. Check your vacuum lines to make sure they are in good shape, connected tightly and not leaking. Clean your battery cables and important engine grounds by removing them, peeling back the ends to reveal and remove any corrosion, and applying dielectric grease. These are normal maintenance items, not expensive to address, and solve many poor-running problems. Also, oxygen sensors get slow with age and lose the ability to work properly without setting any codes. Typical life is 60K miles, but can be shortened by being dropped or struck, or exposed to coolant. Did the last engine die with an internal coolant leak? One more thing - check the plug wire routing to make sure they are correct. Crossed wires can occur when coils are changed and the numbers match the plug positions but the coil numbers are incorrect for the position of the coil.
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