@RmvBfrFlght and
@mikestertwo are two key individuals whom I'd say are experts on this topic. over the years, both have provided excellent input. so there is no need to retype what has already been said.
grassdoc asked what I knew about the spark control module and their variations with all the different stickers and part #'s found on so many GM cars. What's interesting is that in many archived threads on the topic, folks confuse the ignition module (under the coilpak) with these electronic spark control (ESC) modules. Below is from my own archives on the topic.
From the service manual:
Electronic Spark Control (ESC)
This system uses a Knock Sensor in connection with the Electronic Spark Control (ESC) Module and the ECM to control spark timing to allow the engine to have maximum spark advance without spark knock.
ELECTRONIC SPARK CONTROL (ESC) CIRCUIT
3.0L “N“ SERIES; 3.8L “A, C & H” SERIES
3.8L TURBO “G“ SERIES (PORT)
Circuit Description:
The ESC system is comprised of a knock sensor and an ESC module.
The ESC module sends a voltage signal (8 to 10 volts) to the ECM. When the sensor detects detonation, the-module turns “OFF” the circuit to the ECM and the voltage at ECM terminal “B7” drops to 0 volts. The ECM then retards EST as much as 20* in one degree increments, to reduce detonation. Retarded timing can also be a result of excessive valve lifter, pushrod or other mechanical engine or transmission noise.
A loss of the knock sensor signal or a loss of ground at the ESC module would cause the signal at the ECM to remain high. The ECM would control ignition timing (EST) as if no detonation were occurring. The EST would not be retarded, and detonation could become severe enough under heavy engine load conditions to result in pre-ignition and potential engine damage.
Loss of the ESC signal to the ECM would cause the ECM to constantly retard the EST to its max retard of 20* from the spark table. This could result in sluggish performance and cause a Code 43 to set.
Code 43 will set when:
with engine running: ESC input signal has been low more than 2.2 seconds.
It is interesting to note that GM's test procedure for the ESC circuit functionality is to bring the engine rpm to 1500 once engine has reached normal operating temperature. Then, strike the engine block in the area of the knock sensor. If the rpm drops, the electronic spark control module circuit is operating correctly. manual does not specify how big of a hammer to use.
On this forum, RemoveBeforeFlight and Mikestertwo have succinctly reviewed this subject matter previously. It's best to cite their posts on this topic, including the above from RemoveBeforeFlight - no need to type what has already been said well. Below is compiled for convenience in one thread.
1June2010 - mikestertwo:
"The ESC is a frequency filter. It looks for a particular frequency that is predetermined to be knock and sends a signal to the computer. Different modules look for different frequencies. The codes on the modules are specific to a specific frequency range. Who knows what those ranges are "
REFERENCE:
https://www.turbobuick.com/threads/electronic-spark-control-module-esc-help.320257/
15March2008 - mikestertwo:
"It's rare that module goes bad. What your most likey seeing is false knock coming from some other source. Need more info on the car. Is it all stock? What chip is in it? What mods does it have? Assuming the knock is false it could be coming from the down pipe touching the frame, cracked flexplate, valve train noise, ect."
REFERENCE: https://turbobuick.com/threads/possible-esc-problems.244547/
2June2010 - RemoveBeforeFlight:
"Both BSK and HKN modules are a close match to the turbo modules (BLO & HKP). They are from 3.8l Buick carb'd engines. The gain is a tad higher with the other areas matching. Try the BSK first as that is a 4-pole filter while HKN is a 2-pole filter.
REFERENCE:
https://www.turbobuick.com/threads/electronic-spark-control-module-esc-help.320257/
1November2016 - mikestertwo:
"The difference between the BLO and the HKP modules is the HKP module does not attenuate (reduce) the knock frequencies as much as the BLO module which results in a broader frequency band it passes through. The program in the computer chip is the same for either module. The way the chip identifies knock is the number of knock counts from the ESC module over time. This means the chip must see a certain number of knock counts from the ESC module in a certain period of time. The HKP module will pass more knock counts than the BLO module for the same condition. "
"The HKP will pass more knock counts to the ECM which would make it more sensitive than the BLO. "
14November2016 - BEATAV8:
"the knock sensor is a piezo electric crystal which responds to frequency. messing with the grounding can interfere with the frequency which the sensor "thinks" it sees. this is just my opinion.....
if there's absolutely no grounding at all, then yes there should be no signal whatsoever and the ESC should report 9V all the time, no knock retard and no knock counts. Same as having the knock sensor unplugged. "
REFERENCE:
https://turbobuick.com/threads/esc-module-question.445071/
6December2013 - RemoveBeforeFlight:
"Don't go by knock counts, go by knock retard (spark retard). The reason is that there can easily be knock retard without the the ALDL link or the PL showing additional knock counts.
This will occur because the knock counter (PA3) is a 16-bit value (2 bytes). Both the PL and the ALDL link only show the upper byte of the knock counter. There can be several degrees of knock retard with no counts showing.
This is why the knock gauge goes full red when the PL is only showing a count or maybe two. The lower byte (LSB) of the knock counter is incrementing, with spark advance being reduced (knock retard), but the upper byte (MSB, the one we see) hasn't moved yet. Need to get 256 counts before a single count gets registered on the upper counter byte.
How the ESC system (electronic spark control, the knock retard system), works at a hardware level is: there is a 16-bit (2 bytes) hardware counter that runs when the ESC filter reports knock. It runs are 64 KHz, or, 65,536 times a second. The signal from the ESC module is basically digital, it just goes low when reporting knock.
The lower byte (LSB) of the counter, the one we don't see, increments first. After 256 counts then the upper byte gets incremented (MSB), the one we see, to actually report something. The lower byte then rolls over to/past zero and starts over.
In that time the ECM can be pulling spark advance. I say 'can' because under various circumstances knock retard can be held off. "
REFERENCE:
https://turbobuick.com/threads/how-many-esc-counts-is-bad.404845/
Just the operation of the starter motor can add a value to the knock count register.
Following the conversation with grassdoc, I wondered if anyone has specific knowledge of the frequency response of the various modules. Has anyone setup a frequency/function generator, oscilloscope, meter, power source, etc. to simulate "knock" from the sensor in an effort to capture the specific workings of the different modules? How do they compare? I contacted a couple of electrical engineering & electronics hardware folks I thought could shed more light on this topic.
GM was pretty tight-lipped about the specificity of the knock frequencies for each engine's module. It's a pretty crude concept but was effective at reducing the possibility of owners using the cheapest gasoline (lowest octane) and damaging the engine while under warranty. Again, it's really rare for this module to fail, unless it is physically damaged.
While the GNX instrument cluster face stated "PREMIUM FUEL ONLY," there was no such notation on the other turbo buicks. From the engine service manual, the achieved (underrated) performance figures for the 86-87 LC2 engine were the result of minimum (research) octane rating of 91.
With folks today rebuilding engines for 500, 600, 700 horsepower on a street car, the original engine's harmonics have changed. Different pistons and/or rotating assemblies, use of aluminum heads, different valvetrains, the clickety-clack of roller lifters and their dog-bone connectors, timing set replacements (nylon coated cam gear didn't trigger knock sensor), all changed the harmonics of the original engine as delivered. Today, those operating at these higher horsepower levels most likely have XFI or the GN-ecu to better tune.
Even a stock rebuild using different (forged) pistons will change the harmonics. How much? I don't believe anyone knows. And we don't know the specific frequencies for each module. So we carry on with the knowledge mikestertwo and RemoveBeforeFlight have shared regarding this topic.