Trying to understand the knock sensor a little better
08-07-2002, 09:56 AM
#1
Trying to understand the knock sensor a little better
I've been doing some reading on knock sensors on a couple boards. I notice a lot of 4th-genners have been replacing due to the ghost code that doesn't activate the CEL, but is still there when they check for another code.
Knock sensors seem somewhat simple in that they "listen" for knocking/pinging with some sort of microphone, and voltage is adjusted accordingly (in which the ECU then monitors and retards timing if voltage suggests is necessary). I'm assuming by listening, they just listen for some amount of extra noise, and aren't tuned in to a certain frequency that pinging might make. Anyone want to elaborate further on that?
On the sentra boards, and around the net in a few other places, people comment about their factory knock sensors being too sensitive as is. When they do mods that increase sound/vibration in the engine bay (mainly on those that increase sound NEAR the ks), they run into problems with the ks falsley detecting pinging, apparently due just to the increased noise. I'd have to take a look in the haynes to see where our KS is, but I wonder if this is worth any thought to some maxima owners. Some ways around the problem include wrapping the KS in some high-temp insulation material, to desensitize it a bit, and also relocating the KS as far away from noisy areas as possible.
I haven't really seen or read up via search on anyone doing anything like this on the .org. I'm just curious as to how much noise it would take to cause the KS to retard timing, and if it could be made from other sources, such as louder mods, or anything else that makes a noise as loud as pinging near the KS. We have a lot of frequent hesitation issues on the board that can be attributed to a lot of different things. Desensitizing the ks a little seems to be a fairly easy, low-risk job if you use premium fuel, etc, that people might try on hesitation issues if they've tried other things. If for some reason pinging started occurring and the desens'd ks didn't pick it up, you could replace it to its original functionality.
Ideas/thoughts/flames?
Knock sensors seem somewhat simple in that they "listen" for knocking/pinging with some sort of microphone, and voltage is adjusted accordingly (in which the ECU then monitors and retards timing if voltage suggests is necessary). I'm assuming by listening, they just listen for some amount of extra noise, and aren't tuned in to a certain frequency that pinging might make. Anyone want to elaborate further on that?
On the sentra boards, and around the net in a few other places, people comment about their factory knock sensors being too sensitive as is. When they do mods that increase sound/vibration in the engine bay (mainly on those that increase sound NEAR the ks), they run into problems with the ks falsley detecting pinging, apparently due just to the increased noise. I'd have to take a look in the haynes to see where our KS is, but I wonder if this is worth any thought to some maxima owners. Some ways around the problem include wrapping the KS in some high-temp insulation material, to desensitize it a bit, and also relocating the KS as far away from noisy areas as possible.
I haven't really seen or read up via search on anyone doing anything like this on the .org. I'm just curious as to how much noise it would take to cause the KS to retard timing, and if it could be made from other sources, such as louder mods, or anything else that makes a noise as loud as pinging near the KS. We have a lot of frequent hesitation issues on the board that can be attributed to a lot of different things. Desensitizing the ks a little seems to be a fairly easy, low-risk job if you use premium fuel, etc, that people might try on hesitation issues if they've tried other things. If for some reason pinging started occurring and the desens'd ks didn't pick it up, you could replace it to its original functionality.
Ideas/thoughts/flames?
08-07-2002, 10:37 AM
#2
Guest
Posts: n/a
Re: Trying to understand the knock sensor a little better
LS1 (Firebird/Camaro) owners have figured out a way to reduce the sensitivity electrically of the knock sensors. Look here:
http://www.geocities.com/MotorCity/6647/ta93/knock.htm
I don't think wrapping the sensor will reduce the sensitivity. Likely, it would actually be worse due to the porrer mechanical connection with the engine block.
http://www.geocities.com/MotorCity/6647/ta93/knock.htm
I don't think wrapping the sensor will reduce the sensitivity. Likely, it would actually be worse due to the porrer mechanical connection with the engine block.
Originally posted by blizz20oma
I've been doing some reading on knock sensors on a couple boards. I notice a lot of 4th-genners have been replacing due to the ghost code that doesn't activate the CEL, but is still there when they check for another code.
Knock sensors seem somewhat simple in that they "listen" for knocking/pinging with some sort of microphone, and voltage is adjusted accordingly (in which the ECU then monitors and retards timing if voltage suggests is necessary). I'm assuming by listening, they just listen for some amount of extra noise, and aren't tuned in to a certain frequency that pinging might make. Anyone want to elaborate further on that?
On the sentra boards, and around the net in a few other places, people comment about their factory knock sensors being too sensitive as is. When they do mods that increase sound/vibration in the engine bay (mainly on those that increase sound NEAR the ks), they run into problems with the ks falsley detecting pinging, apparently due just to the increased noise. I'd have to take a look in the haynes to see where our KS is, but I wonder if this is worth any thought to some maxima owners. Some ways around the problem include wrapping the KS in some high-temp insulation material, to desensitize it a bit, and also relocating the KS as far away from noisy areas as possible.
I haven't really seen or read up via search on anyone doing anything like this on the .org. I'm just curious as to how much noise it would take to cause the KS to retard timing, and if it could be made from other sources, such as louder mods, or anything else that makes a noise as loud as pinging near the KS. We have a lot of frequent hesitation issues on the board that can be attributed to a lot of different things. Desensitizing the ks a little seems to be a fairly easy, low-risk job if you use premium fuel, etc, that people might try on hesitation issues if they've tried other things. If for some reason pinging started occurring and the desens'd ks didn't pick it up, you could replace it to its original functionality.
Ideas/thoughts/flames?
I've been doing some reading on knock sensors on a couple boards. I notice a lot of 4th-genners have been replacing due to the ghost code that doesn't activate the CEL, but is still there when they check for another code.
Knock sensors seem somewhat simple in that they "listen" for knocking/pinging with some sort of microphone, and voltage is adjusted accordingly (in which the ECU then monitors and retards timing if voltage suggests is necessary). I'm assuming by listening, they just listen for some amount of extra noise, and aren't tuned in to a certain frequency that pinging might make. Anyone want to elaborate further on that?
On the sentra boards, and around the net in a few other places, people comment about their factory knock sensors being too sensitive as is. When they do mods that increase sound/vibration in the engine bay (mainly on those that increase sound NEAR the ks), they run into problems with the ks falsley detecting pinging, apparently due just to the increased noise. I'd have to take a look in the haynes to see where our KS is, but I wonder if this is worth any thought to some maxima owners. Some ways around the problem include wrapping the KS in some high-temp insulation material, to desensitize it a bit, and also relocating the KS as far away from noisy areas as possible.
I haven't really seen or read up via search on anyone doing anything like this on the .org. I'm just curious as to how much noise it would take to cause the KS to retard timing, and if it could be made from other sources, such as louder mods, or anything else that makes a noise as loud as pinging near the KS. We have a lot of frequent hesitation issues on the board that can be attributed to a lot of different things. Desensitizing the ks a little seems to be a fairly easy, low-risk job if you use premium fuel, etc, that people might try on hesitation issues if they've tried other things. If for some reason pinging started occurring and the desens'd ks didn't pick it up, you could replace it to its original functionality.
Ideas/thoughts/flames?
08-07-2002, 10:38 AM
#3
Wow, you're getting quite deep with this KS thing. Anyways, from the Nissan FSM:
"The knock sensor is attached to the cylinder block. It senses engine knocking using a piezoelectric element. Knock from the engine is sensed as vibrational pressure. the KS converts that vibration to a voltagle which the KS sends to the ECU"
Given that, I think it's safe to conclude that the KS won't "hear" much noise b/c it's buried in the block, and it's not really a microphone, because it's picking up vibration and not sound in air.
DW
"The knock sensor is attached to the cylinder block. It senses engine knocking using a piezoelectric element. Knock from the engine is sensed as vibrational pressure. the KS converts that vibration to a voltagle which the KS sends to the ECU"
Given that, I think it's safe to conclude that the KS won't "hear" much noise b/c it's buried in the block, and it's not really a microphone, because it's picking up vibration and not sound in air.
DW
08-07-2002, 10:57 AM
#4
Member
Join Date: Jun 2002
Posts: 30
Since you've already brought up KS sensor, I have a problem: I hear that pinging noise when the tranny shifts from 1 to 2 or 2 to 3 and sometimes in between when I step on the gas a little bit. The mechanic said that he doesn't hear that noise when the engine is in idle (no ****), he said that it might be dirty injectors and such. I decided to use that fuel system cleaner that you add to your gas, the mechanic recommended that also. The noise is still there sometime, and now I'm wondering if it's my KS sensor. Do you know how I can find out for sure and what should I do? Thanks.
08-07-2002, 12:07 PM
#5
Senior Member
Join Date: Sep 2000
Posts: 132
If your ks goes bad, your check engine light will go on. Mine did, and it cost a couple hundred to replace it at the dealership. For about a week, the car would hesitate during acceleration. Then one day, the check engine light just came one while I was cruising on the highway....
08-07-2002, 01:05 PM
#7
dwapenyi - isn't sound technically vibration? hehe...ok, snide/amusing comments aside, I wonder if that could still lead to incorrect reads on the knock sensor, although then technically it would have to be something that vibrated the block I guess.
kev - thanks for the link, I found one other process like that on a site, but not with a script calculator to measure everything out nice for you! now that I finally got my multimeter from harbor freight, maybe I'll put it to use and see if by chance desensitizing the ks leads to any improvements afa hesitation goes (my hesitation could be a number of things though...not too concerned, but if it's fairly easy to try, why not?)
tymah/chitown - I believe the KS alone won't throw the CEL on, but it will register a code that you'll see if you manually pull codes. You can also test the KS. Check this thread out:
https://maxima.org/forums/showthread...+AND+sensitive
Good old DBM, still helping us.
kev - thanks for the link, I found one other process like that on a site, but not with a script calculator to measure everything out nice for you! now that I finally got my multimeter from harbor freight, maybe I'll put it to use and see if by chance desensitizing the ks leads to any improvements afa hesitation goes (my hesitation could be a number of things though...not too concerned, but if it's fairly easy to try, why not?)
tymah/chitown - I believe the KS alone won't throw the CEL on, but it will register a code that you'll see if you manually pull codes. You can also test the KS. Check this thread out:
https://maxima.org/forums/showthread...+AND+sensitive
Good old DBM, still helping us.
08-07-2002, 02:14 PM
#9
Donating Maxima.org Member
Join Date: Feb 2002
Posts: 92
Originally posted by ChiTown Max
If your ks goes bad, your check engine light will go on. Mine did, and it cost a couple hundred to replace it at the dealership. For about a week, the car would hesitate during acceleration. Then one day, the check engine light just came one while I was cruising on the highway....
If your ks goes bad, your check engine light will go on. Mine did, and it cost a couple hundred to replace it at the dealership. For about a week, the car would hesitate during acceleration. Then one day, the check engine light just came one while I was cruising on the highway....
If your KS is too sensitive, meaning it can "hear" engine vibrations a little too well it will not set off the check engine light. It will probably set a KS code, though I don't know what the criteria for setting the code is.
Nissan might have programmed the ECU to record a code any time the KS records a knock, or they might have programmed it after sensing 100 knocks, who knows?
Only someone who is familiar with Nissan ECU programming could answer the question for sure.
What the Firebird guys are doing is adding resistance to the KS circuit thereby reducing its sensitivity. Then the ECU won't try to retard timing.
08-07-2002, 03:55 PM
#10
Senior Member
Join Date: Nov 2000
Posts: 152
Hey TYMAH123. I have the same problem. I have tried several times to get an answer from someone on this forum, but everybody keeps sending me quotes out of some book telling me how my car doesn't ping because it has a knock sensor. My local dealer's tech cannot hear it when he goes out on test drive. I know it is there. It worst when it is hot and the A/C is on.
08-07-2002, 10:21 PM
#12
Yeah, sound is vibration, but the sound that the sensor is detecting is in the block. The KS is picking energy that is powerful enough to rattle metal. The other sounds, like noisy filters or rumbling exhausts are vibrations in the air, so, not quite energetic enough to transfer to the block and false out the KS. The energy transfer from air to metal will be insignificantly small, well, unless you hit some kind of resonance, I guess. Hmmmm.
Those noisy filters and exhausts will also have vibrational energy as well, but compared to a piston knocking, I don't think it's significant enough energy to false the KS.
DW
Those noisy filters and exhausts will also have vibrational energy as well, but compared to a piston knocking, I don't think it's significant enough energy to false the KS.
DW
Originally posted by blizz20oma
dwapenyi - isn't sound technically vibration? hehe...ok, snide/amusing comments aside, I wonder if that could still lead to incorrect reads on the knock sensor, although then technically it would have to be something that vibrated the block I guess.
dwapenyi - isn't sound technically vibration? hehe...ok, snide/amusing comments aside, I wonder if that could still lead to incorrect reads on the knock sensor, although then technically it would have to be something that vibrated the block I guess.
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