tuning a knock sensor and related info


Staff member
* Danny Cabral/Holley EFI manual Said:

Tuning the Knock Sensor Parameters
Knock sensors are designed for use on a factory engine and vehicle. When these sensors are installed in a non-original engine and/or vehicle, the user must be aware of the following:
· Adjustment of the knock sensor parameters may be required such that the ECU can properly distinguish between an actual knock condition, and a non-knock condition. This process is described below.
· Items such as mechanical (solid) cams may introduce noise frequencies into the engine that may inhibit the proper operation of the sensor.
http://mtg-technologies.com/automotives ... 456288.htm

Knock sensors are a device that output a signal to the ECU. This signal contains a spectrum of many different frequencies. The purpose of a knock sensor is to output a signal in a specific frequency range when knock occurs such that the ECU can recognize a knock condition. The signal when knock occurs should have a much larger amplitude (strength) compared to when knock does not exist. This is how the ECU properly determines when knock is and is not occurring. This requires that the proper frequency be input by the user for the specific sensor and application.

There are two basic types of knock sensors: a “Resonant” sensor (which has one wire) and a “Non-Resonant” sensor (which have two wires). Most newer vehicles use a Non-Resonant sensor. These sensors serve the same purpose, but function very differently.
· A 1-wire resonant sensor typically is designed for an intended knock signal frequency. It is affected by the specific engine, chassis, and installation as well.
· A 2-wire non-resonant sensor has a knock output frequency that is primarily driven by the bore diameter of the engine. A chart is provided below to provide the user with a calculated starting frequency.

Setup Parameters
The following Parameters must be set in the software for knock sensors:
Type: Choose from either “1 wire” (Resonant) or “2 wire” (Non-Resonant) sensors.
Number: Select if the engine has 0, 1, or 2 sensors present.
NOTE: If you are not using any knock sensors, make sure you select 0.
Frequency: This is an adjustable parameter. If this value is not the correct value for the specific sensor and application used, engine knock will NOT be detected. It is imperative that this value be entered properly. Information for setting this is below.
Sensitivity: This parameter is used to adjust the scaling of the knock sensor signal. If false knock is being detected, it should be lowered. If actual engine knock is NOT being properly detected, this value can be raised. Start with a value of 50.
“Knock Level” Parameter: The Knock Level parameter can be found in the data monitor and data logger. It is a key parameter when monitoring and tuning knock control. This is a value from 0-100. This value is a reading of the magnitude of the knock sensor output in the frequency range selected. If this value reaches “80” and above, the ECU will read this as a knock event and perform timing retard. Values below “80” are not seen as knock.


Initial Frequency Recommendations
Non-Resonant Sensor
The following table is used to input a baseline knock sensor frequency for a NON-RESONANT (2-Wire) sensor. The “Recommended” selection is the line that you want to use to determine a starting point. The “2nd Choice” would be a second selection if for some reason the recommended frequency does not offer the desired outcome. The “3rd Choice” values can also can indicate knock, but the signal is not as large as the other choices and is typically not used.

To determine the frequency, find the bore diameter in inches for you engine at the bottom of the page (X axis), move up to the “Recommended” line (blue). Move to the left to the Y axis and find the corresponding frequency.
For example, a 5.7L LS1 engine has a bore size of 3.90 inches. This would result in a Theoretical Knock Frequency of 6.0 kHz.
This table offers an excellent starting point for a Non-Resonant sensor. However, tolerances in components and differences in each application may require adjustments.

http://i41.photobucket.com/albums/e300/dcf150/Kn oc...
Resonant Sensor
The proper frequency for a Resonant (1-wire) sensor is mostly dependent on the sensor design itself. The engine and chassis also can alter the best frequency selected. So it is required to find this information in a service manual or other source if a Resonant sensor is used.
The following is a recommended starting point for two common GM Resonant 1-wire sensors:
AC Delco PN 213-3521, GM PN 12589867 – Commonly used on 1998-2006 GM LSx engines. Baseline Frequency – 11.1 kHz
AC Delco PN 213-324, GM PN 10456288 – Used on Late 80’s GM engines. Baseline Frequency – 5.2 to 6.5 kHz

“Tuning” the Knock Sensor Settings
The following is the recommended process for testing and setting proper knock parameters.
1. Per the recommendations above, set the knock sensor parameters.
2. Make sure the base timing table is calibrated such that you will have no knock at any RPM and load. Set the Max Timing Retard  in the ESC parameters to 0.
3. Drive the vehicle and take a data log. Record at idle, cruise, and WOT. Look at the following parameters on a data log:
Knock Level
· Ignition Timing
4. Review the log. You specifically want to look at the Knock Level  parameter. It should never be over 80. If it is (and you didn t actually have real/audible engine knock), you need to lower the â Sensitivity  value until all non-knock conditions result in a Knock Level below 80. When properly adjusted, a WOT knock level value should be around 20-50. Idle may be 0-10.
5. Once the Sensitivity is adjusted properly for non-knock levels, enter Max Timing Retard  Values of 20 (or whatever your preference is).
6. To check for proper knock retard, the ignition timing can now be advanced to a level that induces knock. When knock occurs, the Knock Level should exceed a value of 80 and knock retard should occur. If knock occurs and the knock level is below 80, the Sensitivity is not adjusted properly or the Frequency is not correct.
NOTE: Inducing knock can harm your engine. If you are testing the sensor response by inducing knock, be VERY careful. If your vehicle is too loud to hear audible knock, be very careful. You do not want to operate an engine under a prolonged knock period. Damage can occur immediately in some engines.
7. If the Frequency and Knock level are properly set, the knock retard will respond appropriately and remove timing until the knock is eliminated.

yes you can set lifter pre-load with experience while the engines cold, but in my experience the chances of doing it correctly if your rather new to the process is low.
if you set the lifters on a non-running engine you may find that you need to go back and do it again once the engines been run awhile, this is almost mandatory in my experience.
that knock sensor myth, youll occasionally hear about that says roller rockers can,t be used because the computers knock sensor won,t allow roller rockers, on the Lt1 and LT4 engines, got started because many people can,t correctly adjust valves, especially if your using roller rockers
they leave too much slack in the valve train (usually due to adjusting the valve train while its cold and not adjusting the hydraulic lifter pre-load correctly) and as a result the slight ticking that results is detected as detonation.
once correctly adjusted theres no need to swap knock sensors
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So the ECU retards the timing until there is NO knock, then what??? It must advance the timing again at some point. If it's sampling the sensor several times a second, then wouldn't it be flirting with knock continuously??? Another words, it would be in and out of Knock condition several times per second or what ever the sampling rate is???

I think you should donate your brain to science when your gone. You have way more room in there than most people!!!


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in theory youve set the ignition timing curve and ignition advance on the ignition system so it rarely gets into the detonation threshold, making the knock sensor a seldom used safety net, in a system thats there mostly to compensate for lower than normal octane level fuel

http://www.ecklers.com/corvette-knock-s ... -1996.html





I was reading this topic and was thinking about adding a 1 wire knock sensor (AC Delco PN 213-324, GM PN 10456288 - Used on Late 80s GM engines, Baseline Frequency = 5.2 to 6.5 kHz) to my Gen1 SBC in my 84 Trans Am as a tuning aid (just the sensor screwed into a block drain, a driver circuit or relay, and an LED). I would wire it so that if knock were detected, the relay would latch and remain latched to keep the LED lit until I pressed a momentary push-button to reset the circuit. All the original computer and emission controls will be removed so the car will be just like a carbureted 70s - early 80s GM rear wheel drive with MSD6AL ignition.
I'm really good at detecting the slightest noises and vibrations and strange sounds (or so I thought), because the first time I had this engine in the car, I swear that I only had minor ping and never detonation. But upon disassembly, the rod bearings no longer had their outward crush and the big end of the rods were no longer perfectly round. Maybe I just could not hear the knock over the exhaust, which is why I am considering this. Mike.
range of human hearing

The full range of human hearing WHEN WERE YOUNG extends from 20 to 20,000 hertz."
as we get older we very frequently LOOSE a percentage of that full audible range
ID also point out that some rolling tire noise, some wind noise,etc. also falls in that low hertz range and could easily mask or cover the detonation even if you could in theory hear it occur
(your average muscle car cab sound level reads at well over 80DB under hard acceleration)

most destructive detonation or KNOCK in an engine occurs at and audible range of 1/2 or LESS of the HERTZ RANGE of the LOWEST human HEARING RANGE THRESH HOLD for many adults
(notice on the chart that a 4.1" bore would generally have detonation or pinging at less than 60 hertz)
if your thinking youll hear an engine in detonation PING! youll have to wait until its well past the critical destructive range, thats one reason they developed accurate sensors














as octane levels drop AND/OR when air temperature increase the chance of detonation (KNOCK) INCREASE







85-89 MAF TPI Systems

Below is a list of all the needed sensors to install a MAF TPI setup, and each of their functions.

Mass Air Flow (MAF) Sensor: This sensor is responsible for measuring air volume and density. It is located in the air duct, before the throttle body. All of the air that the engine consumes must first pass through the MAF sensor. At the center of the MAF, is a very thin wire whose resistance increases as it goes up in temperature. A constant voltage is applied to this wire. Air being drawn through the MAF has the effect of cooling this wire, which lowers its resistance, and increases current. As you might suspect, the more air is drawn through the MAF sensor, the greater the current flow. It is important to note that hot dry air is less dense and has less mass than cool moist air. As a result, hot dry air will cool the wire less than cool moist air.

A circuit mounted on the MAF sensor serves to convert the current flow into a variable frequency square wave on 1985 models, which is sent to the ecm. MAF units from 86-89 models output a simple analog signal instead of using frequency modulation like the 1985 units. The ecm will calculate the amount of fuel needed depending on the signal from the MAF sensor. It is very important that there are no air leaks (from a ripped air duct for example) between the MAF and the throttle body.

Oxygen Sensor: Responsible for determining the amount of oxygen in the exhaust manifold. Depending on how much oxygen is in the exhaust, the ecm can determine whether or not the air/fuel mixture is rich or lean. The signal sent to the ecm by the ecm varies between 0.0 and 1.0 volts. An ideal mixture (also known as a Stoichiometric mixture) of 14.7:1 is represented by .450 volts. If the oxygen sensor voltage is below .450, then the air/fuel mixture is lean. Anything over .450 means the mixture is rich. Since the sensor is essentially just a switching device, it will be fluctuating alot between lean and rich. This is normal, and an indication that the sensor is in working properly.
Keep in mind however that oxygen sensors (except wideband oxygen sensors), are not very accurate below or above .450 volts. Exhaust gas temperature will affect the oxygen sensor reading as well. The sensor will not read properly until exhaust gas temperature reaches approximately 600 degrees Farenheit. If you have headers installed, it is a good idea to use a heated oxygen sensor (3 wire) instead of the usual single wire sensor. Headers usually place the oxygen sensor further down the exhaust stream, where exhaust temperatures are cooler. A heated oxygen sensor will heat itself, allowing a more reliable sensor reading than a single wire sensor. If you have factory exhaust manifolds, then the single wire sensor is adequate.

Oxygen sensors are a regular maintenance item, and should be replaced every 30,000 miles. When an oxygen sensor goes bad, it tends to read lean, and will not fluctuate very much. The ecm will attempt to correct this false lean condition by richening the mixture. This will cause poor driveability, and high gas consumption.

Knock Sensor: Also known as detonation sensor, it is responsible for sensing spark knock. Basically, thats when the fuel mixture ignites before the spark plug fires. The piston is moving upwards as this premature combustion takes place. Since fuel is used to cool down the combustion chamber, a lean condition causes the temperature to rise, and ignites the fuel mixture prematurely. This is very abusive on the engine internals, and reduces the life of any engine. The more powerful the engine, the greater the potential for damage. Detonation can be cause by a variety of things. One of the more common causes on TPI retrofits where prom changes have been made to the fuel or spark tables is a lean condition. It isn't always loud enough to be heard, so just because you don't hear any pinging, doesn't mean its not happening.
Detonation will cause a vibration to travel through the engine block. The sensor listens for this vibration at a certain frequency, and sends a signal to the ecm when the frequency is heard. This frequency is different depending on engine size. To prevent possible engine damage, the spark timing needs to be retarded when detonation is present. The sensor itself does not pull the timing back however. The ecm is in charge of retarding the timing, and will do so according to a series of settings inside the prom. The knock sensor is located on the passenger side of the engine block on factory applications. It can however be relocated to the driver side of the block if needed (header clearance for example). They are different depending not only on the size of the engine, but also the ecm being used. It is important that the correct sensor is used to avoid problems. Although it is possible to run the car without one, I strongly suggest against this. I have had customers come to me looking for a $45 knock sensor after spending several hundred dollars and an extra month of work rebuilding a blown engine due to detonation.

Throttle Position Sensor (TPS): Responsible for reporting to the ecm the position of the throttle blades. The ecm will receive a signal which can vary from 0.0 to 5.0 volts. At idle, the TPS should be read .54 volts (factory specification) unless it has been set to a different value inside the prom. If it does not read .54 volts and the idle TPS voltage setting has not been modified in the prom, then it should be adjusted. Under full throttle, it should output close to 5.0 volts. Throughout its range of motion, the voltage should climb steadily, without any jumps or falls. If it is not steady or has some fluctuations as it is moved through its range of motion, it should be replaced. This sensor is located on the passenger side of the throttle body.
Coolant Temperature Sensor (CTS): This is basically a thermistor (means that it changes resistance with temperature) that supplies the ecm with the temperature of the engine coolant. This temperature reading is used for several important functions. The most notable is that the ecm adds extra fuel to an engine when its cold, and as the engine warms up, the extra fuel is reduced. This sensor mounts at the front of the intake manifold. The chart below shows the approximate resistance for this sensor in relation to temperature.


Intake Air Temperature Sensor (IAT): This sensor is also a thermistor (means that it changes resistance with temperature) that supplies the ecm with a temperature reading of the air being drawn into the engine. It is the same as the coolant temperature sensor on 86-92 models. The 1985 intake air temperature sensor used a different connector and cannot be used as a coolant temperature sensor because it had an exposed bulb. This sensor mounts underneath the plenum. The chart above shows the approximate resistance for this sensor in relation to temperature.
Idle Air Control (IAC) Valve: Although this is technically not a sensor at all, people often treat it as one. It is responsible for regulating the amount of airflow being admitted into the engine to adjust engine speed, particularly at idle and deceleration. The ecm controls the IAC at its discretion. The IAC works by moving a cone shaped pintle, which can extend and retract as needed to admit or block off incoming air. The valve moves the pintle in "steps". These steps are numbered and range from 0 to 160. A properly adjust throttle body should be idling when warm between 15-25 steps.

The IAC is used under a variety of conditions, not only at idle speed. The valve mounts on the bottom coolant plate of the throttle body.

Vehicle Speed Sensor (VSS): This is responsible for providing the ECM with the vehicle speed. It can be located either at the tailshaft of the transmission, or behind the speedometer on cars with a cable driven speedometer. It sends a 2k ppm (pulse per mile) square wave signal, and is needed for a variety of functions. It is absolutely critical for the ecm's learn mode, timing retard, emissions, torque converter lockup (automatic lockup transmissions only), idle speed control, and to avoid stalling on deceleration. It is possible to run without one. However, your car will NOT be street legal if you are required to retain emissions equipment, the ecm will not control the torque converter lockup, the ecm will not retard timing if you run into detonation, and it is possible to run into stalling /idle speed issues. In addition, the ecm will not adjust the fuel table properly as you drive (known as its "learning ability"). If the ecm does not know the vehicle speed it is assumed to be 0 mph.

If you still insist on not running a vss, I very highly suggest that the minimum vehicle speed for timing retard be brought down to 0 mph in the prom. The factory setting is 2 or 3 mph. If you don't bring this value down, and you do not run a vss, the ecm will NOT retard your timing under detonation.

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Pay attention to dynamic compression ratio.

Safest bet is to use 100-110-120 motor octane race gas at all times.
Race Full bore against Hellcats and win.
No time to screw with knock sensors.
(notice on the chart that a 4.1" bore would generally have detonation or pinging at less than 60 hertz).
I think you meant 6 KHz. The scale on the left of that graph is in KHz and must be missing a decimal point
because your reference from Danny Cabral/Holley EFI manual says: For example, a 5.7L LS1 engine has a bore size
of 3.90 inches. This would result in a Theoretical Knock Frequency of 6.0 kHz.
So in my case, a 3.766" bore would have a knock frequency of about 6300 Hz, making the 1 wire resonant
AC Delco PN 213-324, GM PN 10456288, used on Late 80s GM engines, Baseline Frequency of 5.2 to 6.5 kHz an acceptable
choice. Thanks for the info.
Digging up all the Old Threads today Grumpy.
Its neat to see our old posts and see and recall what we were thinking at the Time.
Many Times Often I was Thinking Race Car put on the Streets.