I'm looking at adding a knock sensor to my V6 Fiero, so I looked around for information:
https://www.fiero.nl/forum/A...090219-2-084526.html
Unfortunately, I was unable to find any justification to explain why those part numbers are appropriate.

Therefore, I thought we should try to understand the why... at least what we can infer without having inside knowledge.

***MODULES***

The knock module is an "interpreter"; it converts the garbage analog signal from the knock sensor into an on/off knock status. Later model ECMs don't have a separate interpreter, so it must be integrated...

My interest in this is to use the self-contained GM (knock sensor + knock module) system with a dumb MegaSquirt. Interpreting knock is not trivial, so rather than learning how to reliably detect knock, I would prefer to use GM stuff blindly.

GM 16126761 OR GM 16022621(same aftermarket equivalents, probably functionally equivalent)
AIRTEX/WELLS 5F1008
STANDARD MOTOR PRODUCTS LXE9
Applications listed on the Airtex website:
V6-2.8L
V6-3.1L
V8-5.0L
V8-5.7L
This knock module appears to be a general-purpose parts-bin unit.

GM 16052401 OR GM 16128261 (same aftermarket equivalents, probably functionally equivalent)
AIRTEX/WELLS 5F1010
STANDARD MOTOR PRODUCTS LXE6
Applications listed on the Airtex website:
V6-4.3L
V8-5.7L
This knock module was only installed on engines having 4 inch bores.

Here is my speculation. The knock module is an envelope detector, and the envelope output is low-pass filtered, then compared to a threshold noise level. Some hysteresis in the comparator would prevent an unstable output. The comparator output is the on/off knock indication available on pin C.

As for the existence of the 4-inch bore module, I think that some engines with 4-inch bores had false knock readings. Therefore, to only listen to the true knock sounds, an electronic bandpass filter was added to the frontend; a filter with better selectivity than what could be achieved with the selectivity of the knock sensor itself.

So everyone should start with the general-purpose module, and then only if they have false knock issues AND 4 inch bores, then it may be worth trying the special module.

The following MS2/Extra documentation section implies that both styles (general-purpose and 4-inch bore) of knock modules have the same interface to the vehicle, so any differences between the types of modules must be internal:
http://www.msextra.com/doc/...Hardware-3.4-35.html

Does anyone know what kind of output the knock module has? It is push-pull? Can it only source current? Does it output 5V or 12V? From the MS documentation, the knock module can source current, but the rest is unclear. However, not knowing this information won't stop me from buying a module.

I will follow in a second post with my thoughts on the knock sensors themselves.

Apparently, there are multiple GM knock sensors that all share the same physical form factor as the 10456287; all have a 1/4" NPT mounting thread which screws into the water jacket.

The Standard Motor Products catalog is most useful to get a handle on the available knock sensors. Skip to page 145:
http://www.pageturnpro.com/...uide-v2/index.html#1

Knock sensors with same form factor (by visual comparison of the photos), listed by the Standard Motor Products PN:
KS2 (10456287 cross-reference)
KS2T
KS3
KS3T
KS6
KS6T
KS7
KS7T
KS8
KS8T
KS21
KS50
KS61
KS62

I suspect they vary in resonant frequency and possibly Q factor. Or maybe sensitivity? What does the "T" suffix mean? Some may be general-purpose parts-bin parts, some may have been developed to deal with a particular problem of a certain engine.

If other sensors can fit, we should consider them before running straight to the 10456287 without thinking.

Since I doubt we will get specifications (though I can always ask) for the knock sensors, we may consider characterizing the knock sensors ourselves.

This website demonstrates the use of impedance measurements to characterize a knock sensor:
http://www.solaraguy.com/viewtopic.php?t=38336
Not sure how accurate that thread is, considering they mention the Fiero as having a knock sensor

Besides Fieros, I have an interest in audio. I have a PC-based test setup to measure the Thiele-Small parameters of speakers. With the test setup, I can test the impedance (magnitude and phase) of a DUT (typically a woofer) over the audio frequency range.

I should be able to use my test rig to characterize a knock sensor. I would like to measure the resonant frequency and Q of each unit.

Here is the test setup: Screw sensor into block, then fill water jacket with enough water to at least submerge the sensor. I don't know if the water adds any significant damping to the knock sensor response, but I would perform the test with water, just in case.

Ideally, I would purchase all 14 sensors and characterize them all. However, I am a bit too cheap to do this
I could potentially test a handful though, and then if people want to pitch in by shipping me uncharacterized knock sensors from the list, we could collectively complete the list, which I believe would be valuable to us as tuners.

From the solaraguy thread above (the same formula appears elsewhere), here is a formula to estimate (within a few hundred Hz) the knock frequency of an engine based on the bore size:
Frequency in kHz = 573 / Bore in mm

Once you know the knock frequency of the engine, choose a knock sensor having the same (or close) resonant frequency.

The formula is a bit of a hillbilly method. The real method to determine the knock frequency is to provoke knock in your engine of choice, and then record the knock frequency. However, you may kill some engines doing it the proper way...

Another approach is to copy what the factory did, if you can find a close match to your setup. I will be building a 3.1 with iron heads and a later-model block (459 casting number). If I can find a factory engine like mine, that was equipped with a knock sensor, then I can simply use that knock sensor.

Also, while it may take a fair amount of work, we may be able to correlate each part number with the bore diameters of the engines they were installed on. Though that may be too much work for the quality of the data we shall obtain that way.

On a side note, I was thinking of getting a Cloyes double roller chain, since the silent chains seem to stretch a lot, but I am unsure if the noise will be picked up by the knock sensor.

The "T" suffix means that it's the cheap commercial grade. So we can remove those from our list.

KS2 (10456287 cross-reference)
KS3
KS6
KS7
KS8
KS21
KS50
KS61
KS62

Scroll down to read the interesting post by JohnAtJandS (Automotive):
http://www.eng-tips.com/viewthread.cfm?qid=54276

So in the late 80s/early 90s, there were three frequencies:
5.2kHz
6.0kHz
7.0kHz

Unfortunately, it will be difficult for us to match these frequencies with the corresponding part numbers.

Presumably, the bandwidths would have been wide enough to overlap each other; so that any engine could be matched to a suitable knock sensor. This means we don't have to be perfect with our choice of knock sensor.

I checked the following iron-headed vehicles, and they all use the status quo AIRTEX 5F1008 and STANDARD KS2 combo, from the factory:
CHEVROLET 1993 S10 PICKUP 2.8
CHEVROLET 1986 S10 BLAZER 2.8
CHEVROLET 1991 LUMINA APV 3.1
PONTIAC 1994 TRANS SPORT 3.1

Good enough for me, the status quo 5F1008 + KS2 is validated! So these parts will make it onto my Fiero 3.1.

As an interesting observation, the 80s Camaro 305 engines use the same exact module + knock sensor combo.

However, the 80s Camaro 350 engine uses the 5F5010 + KS7 ... goes to show that the bore diameter is key.

Now I just need to figure out how to hook up the digital output, but that should be a walk in the park.

My recollection is that only the 1985 ECM had provision to interpret a knock sensor, so I assume that you are looking for a unit that will go between the sensor and whatever you are using as a computer. Best to ask Megasquirt if there is an interface.

I use an MSD sensor display and manual timing control in a race car, but I assume you want something automatic.

Yeah, I was looking for a standalone knock interpreter module that would work with my MegaSquirt 2. The GM module seems to be the hot ticket, since it will easily interface with the MS2.

As long as you use a factory combination (or close to it) of the following parts:
engine block & heads -----> knock sensor -----> knock interpreter module

...you should have a knock sensing system that works out of the box, with factory-level reliability. Mixing parts is unlikely to work well; everything needs to be designed to work together.

MS3 can be equipped with a built-in universal knock sensor interpreter, but it would need to be tuned for the particular engine/knock sensor combo. While I like tuning... I imagine that tuning a knock sensor could be destructive.

I'm going to turbocharge my car, so it's worth going through this exercise.