knock sensor
04-09-2010, 08:37 PM
#1
knock sensor
Ok I know the purpose of a knock sensor, but i want to know what really happens when the knock sensor goes bad? Like can it really hurt the engine in anyway? I have an code for the knock sensor, and I know replacing it requires taking off upper and lower intake manifolds,and I don't wanna go in there if the knock sensor being bad doesn't make a difference.
04-09-2010, 09:08 PM
#2
From what I've always understood when knock occurs it sends a signal to the ECU to adjust the dynamics of the motor in some way. (Sort of like a self correcting system I believe) May be off. I just know that long term knock is a no no. No point in being here as a supposed enthusiast and you neglect your car. Oh and when digging for that ks yes you have to remove your upper and lower IM but don't forget you have to remove that damn water pipe from the water pump to the thermostat.
GL
GL
04-10-2010, 05:44 AM
#3
From what I've always understood when knock occurs it sends a signal to the ECU to adjust the dynamics of the motor in some way. (Sort of like a self correcting system I believe) May be off. I just know that long term knock is a no no. No point in being here as a supposed enthusiast and you neglect your car. Oh and when digging for that ks yes you have to remove your upper and lower IM but don't forget you have to remove that damn water pipe from the water pump to the thermostat.
GL
GL
04-10-2010, 06:46 AM
#5
If the knock sensor is bad on a VE, timing will stay retarded when it should be advanced, you'll have a huge loss of power in the low end at times. If you aren't experiencing this, no reason to replace it atm. If it does this, you can shut off the engine and restart it, might go back to normal for a few minutes.
04-10-2010, 09:27 AM
#6
If the knock sensor is bad on a VE, timing will stay retarded when it should be advanced, you'll have a huge loss of power in the low end at times. If you aren't experiencing this, no reason to replace it atm. If it does this, you can shut off the engine and restart it, might go back to normal for a few minutes.
04-10-2010, 11:36 PM
#7
Senior Member
Join Date: Oct 2004
Location: Pretoria - South Africa
Posts: 1,205
I think you guys need to read the FSM ................. top of part EF+EC 171.
Nobody can say what happens exactly when a KS fails because it has more than one failure mode.
1. It can fail open circuit - in this case the ECM will not retard the normal timing maps at all - it will/may complain that its not "seeing" the KS though.
2. It can fail short circuit - highly unlikely due to the KS design characteristics and the ECM will react the same way as in #1 above.
3. It can fail in such a way as to be producing random pulses that has no relationship to genuine knock on the motor - in this case the ECM will incorrectly be told by the funky pulses that there is knock present and it will continue to retard timing as far as its design allows (10+ degrees?) - this is the probably the most common failure mechanism.
For the record - the KS is not responsible for dynamic timing adjustment on the 3rd gens at all - in this application its a safety device for protection of the motor - if the KS would never fail and if you always kept your engine tuned properly and fed it only good quality fuel, then the KS would have have served no purpose on the 3rd gen at all.
Nobody can say what happens exactly when a KS fails because it has more than one failure mode.
1. It can fail open circuit - in this case the ECM will not retard the normal timing maps at all - it will/may complain that its not "seeing" the KS though.
2. It can fail short circuit - highly unlikely due to the KS design characteristics and the ECM will react the same way as in #1 above.
3. It can fail in such a way as to be producing random pulses that has no relationship to genuine knock on the motor - in this case the ECM will incorrectly be told by the funky pulses that there is knock present and it will continue to retard timing as far as its design allows (10+ degrees?) - this is the probably the most common failure mechanism.
For the record - the KS is not responsible for dynamic timing adjustment on the 3rd gens at all - in this application its a safety device for protection of the motor - if the KS would never fail and if you always kept your engine tuned properly and fed it only good quality fuel, then the KS would have have served no purpose on the 3rd gen at all.
04-11-2010, 12:11 AM
#8
04-11-2010, 01:19 AM
#9
Senior Member
Join Date: Oct 2004
Location: Pretoria - South Africa
Posts: 1,205
From a technical stance:
The KS is a piezo crystal - it will produce voltage "spikes" when excited vigorously enough at its resonant frequency - "knock" on the motor contains frequency components at the crystals resonant frequency - thus, when knock is present the ECU "sees" the voltage spike - after filtering in the ECU, if the spike is of adequate amplitude and short enough, the ECU interprets that as a condition requiring timing delay.
FWIW - I can unplug my KS on my 3rd gen and the timing doesn't change an iota throughout the whole rev range basically confirming my description above.
Guess you are entitled to your opinion based on different experiences? - if so please share and set me straight
04-11-2010, 08:00 AM
#10
From a technical stance:
The KS is a piezo crystal - it will produce voltage "spikes" when excited vigorously enough at its resonant frequency - "knock" on the motor contains frequency components at the crystals resonant frequency - thus, when knock is present the ECU "sees" the voltage spike - after filtering in the ECU, if the spike is of adequate amplitude and short enough, the ECU interprets that as a condition requiring timing delay.
FWIW - I can unplug my KS on my 3rd gen and the timing doesn't change an iota throughout the whole rev range basically confirming my description above.
Guess you are entitled to your opinion based on different experiences? - if so please share and set me straight
The KS is a piezo crystal - it will produce voltage "spikes" when excited vigorously enough at its resonant frequency - "knock" on the motor contains frequency components at the crystals resonant frequency - thus, when knock is present the ECU "sees" the voltage spike - after filtering in the ECU, if the spike is of adequate amplitude and short enough, the ECU interprets that as a condition requiring timing delay.
FWIW - I can unplug my KS on my 3rd gen and the timing doesn't change an iota throughout the whole rev range basically confirming my description above.
Guess you are entitled to your opinion based on different experiences? - if so please share and set me straight
I think what you seen in the fsm is what happens if it's open or short circuit, not really failing knock sensor.
04-11-2010, 08:55 AM
#11
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Join Date: Oct 2004
Location: Pretoria - South Africa
Posts: 1,205
Well yea timing doesn't just change when you unplug it like my timing is still at 15 degrees even with the code, but if the ECU decided it wanted to make more power it would advanced timing to like 17 degrees or even more till it hears a ping then it retards till pinging stops.
Read the FSM again - the ECU basically runs the advance curves according to a factory pre-programmed map. When the KS is functioning properly on a motor in good tune according to the FSM specs and running on quality fuel, the ECU doesn't use it in any advance or retard strategy at all
04-11-2010, 09:34 AM
#12
No it wont because that is not the function of the KS and its also not the way the ECU controls timing - on the design of the 3rd gen anyway.
Read the FSM again - the ECU basically runs the advance curves according to a factory pre-programmed map. When the KS is functioning properly on a motor in good tune according to the FSM specs and running on quality fuel, the ECU doesn't use it in any advance or retard strategy at all
Read the FSM again - the ECU basically runs the advance curves according to a factory pre-programmed map. When the KS is functioning properly on a motor in good tune according to the FSM specs and running on quality fuel, the ECU doesn't use it in any advance or retard strategy at all
. Just sounds a little weird.
04-11-2010, 09:43 AM
#13
You can take the sensor out easily by making a simple tool. Just weild the wrench(i think 12mm) to an extension and bend it sort of like an s so that it will fit in. Basicly just use that to break the seal, then you can gett in there with other tools. It saves ALOTT of either time or money.
04-11-2010, 12:17 PM
#14
From a technical stance:
The KS is a piezo crystal - it will produce voltage "spikes" when excited vigorously enough at its resonant frequency - "knock" on the motor contains frequency components at the crystals resonant frequency - thus, when knock is present the ECU "sees" the voltage spike - after filtering in the ECU, if the spike is of adequate amplitude and short enough, the ECU interprets that as a condition requiring timing delay.
FWIW - I can unplug my KS on my 3rd gen and the timing doesn't change an iota throughout the whole rev range basically confirming my description above.
Guess you are entitled to your opinion based on different experiences? - if so please share and set me straight
The KS is a piezo crystal - it will produce voltage "spikes" when excited vigorously enough at its resonant frequency - "knock" on the motor contains frequency components at the crystals resonant frequency - thus, when knock is present the ECU "sees" the voltage spike - after filtering in the ECU, if the spike is of adequate amplitude and short enough, the ECU interprets that as a condition requiring timing delay.
FWIW - I can unplug my KS on my 3rd gen and the timing doesn't change an iota throughout the whole rev range basically confirming my description above.
Guess you are entitled to your opinion based on different experiences? - if so please share and set me straight
A while ago I set the ign timing to ~20 degrees adv at idle on my friends VE. It ran like bat out of hell when it was cold outside. When the weather was really warm it would ping a bit between 3-4k rpm. He always used 92 octane. If I unplugged the ks, it wouldn't ping anymore and it would be down on power. I decided to hook the ks up to a switch. When the switch was turned on, the ks would be connected and functioning. When the switch was turned off, the ks would be disconnected. This switch made it to where he could have the best of both worlds, extra hp when the weather was cool and he wouldn't have to worry about pinging when it was hot outside.
Another thing to consider. 99% percent of the time, a maxima's KS fails due to corrosion of the electrical connector pins, not the ks itself. The corrosion creates such a high resistance, it's virtually like having an open circuit. What I'm saying is, almost every time someone's ks is considered "bad," it's actually an open ks circuit, yet they complain of power loss. When they replace the ks and harness or install a ~550k ohm resistor, the power is revived.
04-11-2010, 12:22 PM
#15
Senior Member
Join Date: Oct 2004
Location: Pretoria - South Africa
Posts: 1,205
Cheers for that experience then 505max94se - did you perhaps measure to see what sort of retard you got when unplugging the KS? Do you know if it was a fixed retard value over the whole rev range or if there was some other retard characteristic/strategy exhibited with the KS unplugged?
Last edited by LvR; 04-11-2010 at 12:37 PM.
04-11-2010, 12:40 PM
#16
Here's the timing and fuel maps for a stock VE.
The timing adv values >100 are where the ecu looks for knock. To get the true timing adv values where the ecu looks for knock, IIRC, you subtract 128.
The timing adv values >100 are where the ecu looks for knock. To get the true timing adv values where the ecu looks for knock, IIRC, you subtract 128.
04-11-2010, 12:42 PM
#17
Cheers for that experience then 505max94se - did you perhaps measure to see what sort of retard you got when unplugging the KS? Do you know if it was a fixed retard value over the whole rev range or if there was some other retard characteristic/strategy exhibited with the KS unplugged?
Yes, it's a fixed retard value (as shown in my post above).
04-11-2010, 09:12 PM
#19
The 3rd gen KS has a much simpler purpose than those found on modern engine management systems, and is simply reflecting the state of technology at the time of the 3rd gen engine management design - nothing weird about it at all. I also have eg a 3L straight 6 Opel motor with the same purpose for the KS ................ protection only
Cheers for that experience then 505max94se - did you perhaps measure to see what sort of retard you got when unplugging the KS? Do you know if it was a fixed retard value over the whole rev range or if there was some other retard characteristic/strategy exhibited with the KS unplugged?
Cheers for that experience then 505max94se - did you perhaps measure to see what sort of retard you got when unplugging the KS? Do you know if it was a fixed retard value over the whole rev range or if there was some other retard characteristic/strategy exhibited with the KS unplugged?
04-11-2010, 10:14 PM
#20
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Join Date: Oct 2004
Location: Pretoria - South Africa
Posts: 1,205
"Detects" is correct yes - ............... the ECU however ignores the KS when all is well on the motor though - if you have a look at the timing maps 505max94se posted there, its quite obvious that a real simple retard strategy is applied when knock is detected under higher engine loads - the engine simply runs on a different set of advance map values.
When the motor is shut down, the standard advance map is again restored and used till the KS again reports knock presence, when the simple advance maps with knock catered for start to be used again.
As soon as you have more than one FIXED map featuring in the advance control strategy, you can be sure the KS doesn't form part of an active closed loop and continuously adjustable advance strategy - the ECU in our case effectively simply looks up the relevant load and speed input and then sets the advance according to the value found in the map. On later and more modern and advance control systems, you will find the ECU continuously tuning the advance maps - those control systems will often create a dynamic advance map by employing an intelligent learning and storing of knock onset advance values for the particular fuel currently used in the engine - it often takes days and quite a few kilometers traveled for the ECU to effectively adjust to a different quality of fuel. On the 3rd gens, if you swap a good KS into the bad KS position, you will immediately feel/see the difference since the normal advance curve map is immediately used
04-11-2010, 11:27 PM
#21
You can take the sensor out easily by making a simple tool. Just weild the wrench(i think 12mm) to an extension and bend it sort of like an s so that it will fit in. Basicly just use that to break the seal, then you can gett in there with other tools. It saves ALOTT of either time or money.
04-12-2010, 02:56 PM
#22
Probably the same FSM you are? .................
"Detects" is correct yes - ............... the ECU however ignores the KS when all is well on the motor though - if you have a look at the timing maps 505max94se posted there, its quite obvious that a real simple retard strategy is applied when knock is detected under higher engine loads - the engine simply runs on a different set of advance map values.
When the motor is shut down, the standard advance map is again restored and used till the KS again reports knock presence, when the simple advance maps with knock catered for start to be used again.
As soon as you have more than one FIXED map featuring in the advance control strategy, you can be sure the KS doesn't form part of an active closed loop and continuously adjustable advance strategy - the ECU in our case effectively simply looks up the relevant load and speed input and then sets the advance according to the value found in the map. On later and more modern and advance control systems, you will find the ECU continuously tuning the advance maps - those control systems will often create a dynamic advance map by employing an intelligent learning and storing of knock onset advance values for the particular fuel currently used in the engine - it often takes days and quite a few kilometers traveled for the ECU to effectively adjust to a different quality of fuel. On the 3rd gens, if you swap a good KS into the bad KS position, you will immediately feel/see the difference since the normal advance curve map is immediately used
"Detects" is correct yes - ............... the ECU however ignores the KS when all is well on the motor though - if you have a look at the timing maps 505max94se posted there, its quite obvious that a real simple retard strategy is applied when knock is detected under higher engine loads - the engine simply runs on a different set of advance map values.
When the motor is shut down, the standard advance map is again restored and used till the KS again reports knock presence, when the simple advance maps with knock catered for start to be used again.
As soon as you have more than one FIXED map featuring in the advance control strategy, you can be sure the KS doesn't form part of an active closed loop and continuously adjustable advance strategy - the ECU in our case effectively simply looks up the relevant load and speed input and then sets the advance according to the value found in the map. On later and more modern and advance control systems, you will find the ECU continuously tuning the advance maps - those control systems will often create a dynamic advance map by employing an intelligent learning and storing of knock onset advance values for the particular fuel currently used in the engine - it often takes days and quite a few kilometers traveled for the ECU to effectively adjust to a different quality of fuel. On the 3rd gens, if you swap a good KS into the bad KS position, you will immediately feel/see the difference since the normal advance curve map is immediately used
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