Originally Posted by Danny Cabral
I recently tuned my knock sensors and they're functioning great! I attached an excerpt of the tuning manual below. I'm using dual GM 10456288 knock sensors wired to a Holley Dominator ECU. I consider this to be a good universal knock sensor; I even had good results from it with the C950. The sensor's frequency is 10.5 kHz as determined in this LINK (thanks to Big Moose at MTG Technologies LLC), and I finished tuning the Sensitivity with a value of 25. After testing, I chose to program 4° of knock retard. The ESC Parameter's Max Timing Retard table, allows you to enter the amount knock retard on its 8x8 (MAP x RPM) table. This is a great feature, because sometimes knock sensors will read false knock at certain RPM or load (especially on high performance engines), so you want to enter zero in those cells. The idle area should be at zero anyway.

Tuning the knock sensor Sensitivity required me to force my engine to "ping" (not "knock"). On a hot summer day, I fueled my truck with lower octane fuel, disconnected my cold air induction and drove up a steep hill to tune the Sensitivity. Tuning the Sensitivity isn't difficult (read tuning procedure below). After tuning for almost an hour, I achieved a condition where the Knock Level is only above 80% during actual pinging and the knock sensors eliminate it with 4° of timing retard. I'm very happy with the results.
UPDATE: I discovered the Sensitivity of new knock sensors will be slightly higher than used knock sensors. As the knock sensor ages, the Sensitivity value will need to be slightly decreased due to the increased amplitude of the internal piezoelectric crystal.

Originally Posted by Holley EFI "Help" Contents
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.

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.
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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:
ACDelco PN 213-3521, GM PN 12589867 – Commonly used on 1998-2006 GM LSx engines. Baseline Frequency – 11.1 kHz
ACDelco PN 213-324, GM PN 10456288 – Used on Late 80s 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
· RPM
· MAP
· TPS
· 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 “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.
Originally Posted by Danny Cabral
If you're like me and you don't want to cut the Holley EFI harness (to use conventional crimp connectors),
then you must purchase the Delphi Metri-Pack 150 connector parts & crimping tool (don't buy the expensive one).
Delphi 12110293 3-cavity connector
Delphi 12052845 TPA lock
Delphi 12048074 wire terminal(s)
Delphi 15324976 wire seal(s)
Delphi 12059168 cavity plug(s)

NOTES:
Terminal "C" of the main harness knock connector, is never connected to chassis ground. It's the 2-wire knock sensor's ground wire. If you're using a 1-wire knock sensor, connect that wire to terminal "A". If you're using two 1-wire knock sensors (as I am), connect one sensor to terminal "A" and the other sensor to terminal "B". 1-wire knock sensors don't use terminal "C" at all; that's what the cavity plug(s) are for.

If using the 1-wire knock sensors, like the ones discussed here, the only wiring required is a knock sensor pigtail:
GM 12102621 or ACDelco PT308, shown below. (Also for early coolant temp sensors & fan sending units.)
Evidently, there was once a high temperature version available, GM 12126456 or ACDelco PT727.
http://www.summitracing.com/parts/SMP-S550/ (Standard Motor Products S550):




Originally Posted by Danny Cabral
90° Knock Sensor Adapter - I've also been contacted in reference to my custom made 90° adapter to mount the knock sensor close to the lower block. I made it using a 90° 1/4" NPT brass elbow fitting. Simply cut off the male threads and drill straight through using the appropriate drill bit for 3/8"-16 or 7/16"-14 bolts. (A 1/4" NPT Street Tee fitting can be used the same way, if a little raised clearance is necessary.) I mounted it on an existing raised threaded boss with a grade 8 bolt. The advantages are; the knock sensor hugs the side of the block (providing the necessary starter and/or header clearance), it swivels to aim it at a convenient angle (aids in routing the wire), and it doesn't require draining the coolant. My datalogs prove it's functional.

My dual knock sensor mounting locations:
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Originally Posted by Danny Cabral
Phantom Knock - A false triggering of the knock sensor due to an engine's particular vibrational noise at certain RPM/loads. This usually occurs on light acceleration or at mid-range engine operation. Typical causes; valvetrain components (solid lifters, camshaft gear-drives, incorrect rocker arm geometry, etc.), piston-to-cylinder clearances, excessive bearing clearances, mechanical fuel pumps (non-EFI), exhaust systems, solid motor mounts, loose suspension/driveline components contacting exhaust/engine, etc. Knock senors aren't perfect and modified engines can worsen this condition.

Burst Knock
- A phenomenon that can occur during sudden increases in engine load (sudden onset of high torque-WOT). The rapidly rising cylinder pressures may lead to knock under what would otherwise be stable combustion under steady-state engine operation. Many OEMs anticipate this and intentionally program their ECUs to retard timing a few degrees during these acceleration periods.

There's a lot of misinformation concerning knock sensing hardware. For a thorough lesson, read this SAE Technical Publication:
"Combustion Knock Sensing - Sensor Selection and Application Issues" http://www.sae.org/technical/papers/900488

Three basic types of vibrational (piezoelectric crystal) knock sensors:
• FLAT RESPONSE - High resonant frequency, resulting in a relatively flat response (5-8 kilohertz). Universal in nature but requires a very specific controller/module for each engine model.
• SPIKE RESONANT - Centered on mean knock frequency of the engine, capitalizing on built-in mechanical amplification & filtering characteristics (narrow bandwidth-100 hertz) and are tuned to the knock frequency of particular engines. Limited to manufacturing variations in sensor and/or engine, which causes inaccuracy of the knock frequency response, resulting in undetected knock events.
• BROADBAND RESONANT - Similar to spike sensors but combines the advantages of spike & flat type sensors. Their mechanical amplification & filtering of the signal, over a broad bandwidth in the knock range, provides high signal levels while allowing for typical sensor & engine variations. Broadband sensors are also less susceptible to engine noise and vibration (that would fool a flat sensor) due to their ability to distinguish false signals with their high frequencies.

Knock frequency is a function of cylinder bore diameter but I've found that application selection isn't as critical with broadband sensors. As a matter of fact, in my research, I noticed each model Delco Remy broadband sensor was used in a multitude of GM engines (ranging from V6's to big block V8's). Also, the GM #10456288 knock sensor is used in MSD's Engine Knock Alert kit #8964.

Recommended Mounting Locations:
• Choose a stiff, centrally located portion of the lower engine block.
• Position away from noisy components, such as valvetrain & accessory drives.
• Stiff locations between two cylinders are better than cylinder centers.
• Locate away from high exhaust heat and harsh weather & road environments.

http://diagnosticnews.com/engine-knock-sensors-part-1/ (Engine Knock Sensors, part 1)
http://diagnosticnews.com/engine-knock-sensors-part-2/ (Engine Knock Sensors, part 2)