Knock Signal
09-10-2003, 02:28 AM
#16
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The tap on engine and look for timing retard is mentioned in the factory manuals.
The Led used on Mitsubishi's to indicate knock is not tied to the knock sensor. The ECU in the Mitsubishi sends a pulse with modulated output to a solenoid that reduces boost pressure by directing more "boost signal" to the wastegate(kind of like the 944 turbo control valve). The LED is wired parallel to the solenoid. Mitsubishi turbo cars drop boost first to reduce knock then timing.
The Led used on Mitsubishi's to indicate knock is not tied to the knock sensor. The ECU in the Mitsubishi sends a pulse with modulated output to a solenoid that reduces boost pressure by directing more "boost signal" to the wastegate(kind of like the 944 turbo control valve). The LED is wired parallel to the solenoid. Mitsubishi turbo cars drop boost first to reduce knock then timing.
09-13-2003, 01:45 AM
#17
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Just a heads-up to everyone. Before you guys try tackling a monitoring device, check and make sure your existing one is good. I found out mine was bad after sorting through the parts to start rebuilding my motor. Maybe I wouldn't be rebuilding it if it had been good....? Just a recommendation; it only needs to be installed with 6-7#'s torque, be sure to use the same bolt too.
09-13-2003, 07:49 AM
#18
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Bosch knock sensors are not tuned against specific knock frequencies.
In fact Bosch markets them as "Piezoelectric vibration sensors, Measurement of structure-borne noise/acceleration"
Bosch states the following areas of application:
Knock control, Protection of machine tools, Detection of cavitation, Monitoring of bearings and Theft deterrent systems.
They have a measuring range of 1-20 khz.
Bosch also markets a Signal evaluation module for the knock sensors.
This module has a programmable bandpass filter that determines what frequencies it measures.
It would be interesting to know if the KLR does the filtering in hardware or software. I would guess that it's hardware and if so, it would be easy to tap into the signal path after the filter.
Has anyone got a circuit diagram of the KLR?
In fact Bosch markets them as "Piezoelectric vibration sensors, Measurement of structure-borne noise/acceleration"
Bosch states the following areas of application:
Knock control, Protection of machine tools, Detection of cavitation, Monitoring of bearings and Theft deterrent systems.
They have a measuring range of 1-20 khz.
Bosch also markets a Signal evaluation module for the knock sensors.
This module has a programmable bandpass filter that determines what frequencies it measures.
It would be interesting to know if the KLR does the filtering in hardware or software. I would guess that it's hardware and if so, it would be easy to tap into the signal path after the filter.
Has anyone got a circuit diagram of the KLR?
09-16-2003, 01:21 AM
#19
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My money is on the KLR not really doing any filtering. It *might* have a BPF on the resonant knock frequency and *maybe* some of its harmonics. Odds are, however, that it is just a simple first order BPF from maybe 2kHz-20kHz followed by an integrator and some gain stage and then tied in to an A/D. The stock system is not very complex by any means.
09-16-2003, 08:19 PM
#20
Race Director
Remember that knock isn't a binary yes/no, all-or-nothing, black & white condition. What the knock sensor does is picks up ALL engine noises and it's the filtering electronics that must pick out instances of knock. Even then, there are varying degrees of knock. Simply from looking at the numbers of blown headgaskets on 951s, one can tell that the stock system does not work that well.
First, if you want to monitor knock, it can not be a simple single-LED display. It should varying amounts of engine noise, such as our Knock-Link display. This unit has 4 distinct LEDs which light up at various levels of noise. The adjustable trim-**** should be used to set to light up the 1st green LED under normal engine-operating conditions. At high-RPMs, there's more noise and the displays the 2nd green LED. As one enters the grey area surrounding detonation and knock, the yellow lights up. When knock & detonation occurs, the noise is increased substantially and it lights up the red LED.
Second, having a knock indicator is fine, but how are you going to tune the car with that in mind? Fuel should have already been optimized for best power around 12.0-12.5:1 AFR. Increasing fuel beyond that to combat knock & detonation is a broad sweep-it-under-the-carpet desperate approach at combating knock because it kills power very easily. Best to retard the ignition a little.
To gain optimal ignition maps, one must use a steady-state dyno that can hold the car at any specific load and RPM zone. This allows you to measure torque output at each zone in the 3D map. Start conservatively with not much advance and slowly increase ignition. At some point, you'll see the yellow LED light up indicating the onset of knock. You'll also notice that the TQ number starts to drop. Any more ignition will result in the red knock LED going off and a more significant drop in TQ. So you can set ignition a couple degrees below the onset of nock in that zone. Then adust the dyno to the next load X RPM zone and test for best TQ there as well. There's 144 cells in the stock Motronics ignitoin map and each one needs to be optimized. Aftermarket EFI systems with finer cells in 100rpm increments will give you more zones that needs to be adjusted.
First, if you want to monitor knock, it can not be a simple single-LED display. It should varying amounts of engine noise, such as our Knock-Link display. This unit has 4 distinct LEDs which light up at various levels of noise. The adjustable trim-**** should be used to set to light up the 1st green LED under normal engine-operating conditions. At high-RPMs, there's more noise and the displays the 2nd green LED. As one enters the grey area surrounding detonation and knock, the yellow lights up. When knock & detonation occurs, the noise is increased substantially and it lights up the red LED.
Second, having a knock indicator is fine, but how are you going to tune the car with that in mind? Fuel should have already been optimized for best power around 12.0-12.5:1 AFR. Increasing fuel beyond that to combat knock & detonation is a broad sweep-it-under-the-carpet desperate approach at combating knock because it kills power very easily. Best to retard the ignition a little.
To gain optimal ignition maps, one must use a steady-state dyno that can hold the car at any specific load and RPM zone. This allows you to measure torque output at each zone in the 3D map. Start conservatively with not much advance and slowly increase ignition. At some point, you'll see the yellow LED light up indicating the onset of knock. You'll also notice that the TQ number starts to drop. Any more ignition will result in the red knock LED going off and a more significant drop in TQ. So you can set ignition a couple degrees below the onset of nock in that zone. Then adust the dyno to the next load X RPM zone and test for best TQ there as well. There's 144 cells in the stock Motronics ignitoin map and each one needs to be optimized. Aftermarket EFI systems with finer cells in 100rpm increments will give you more zones that needs to be adjusted.
