GM ESC modules and matched knock sensors.

I know it's up to me to see whats best for my system but I wanted to know what experience is out there with false knock or overly sensitive system. 383 TPI (EBL) in 89 K1500. Was using BLH ESC module with correct knock sensor for vehicle (mismatch), I am going to try going back to the correct ESC module and log, has the matched knock sensor for the BLH module proved to be best, just want to be sure before purchasing ACD 213325, have ACD 213324 installed with 45deg elbow. Robert R says they will work together, my reading suggests match components.

The unfortunate truth is that once you start changing components around, you lose the "precision" of the knock module intended for the original application. The module is a filter that rejects certain frequencies and allows others, converting this into a simple on/off for the ECM/PCM to read as knock. The only "right" way to get a knock module to work with a particular custom setup is to use a scope on the knock sensors to monitor knock and then induce some on purpose on a dyno, note the frequency range, and then create your own knock module accordingly. Which...yanno, kind of out of reach of just about everyone since at the moment, the knock modules are something of a black box, not to mention the skill required.

I do wish you the best of luck though. Maybe you'll get lucky and there'll just happen to be an existing module that works decently for you.

I have 3 or 4 EC modules I can try and log, easy swap.

http://www.gearhead-efi.com/Fuel-Inj...ESC-and-swaps!
http://www.gearhead-efi.com/Fuel-Inj...-(My-91-C1500)

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Which...yanno, kind of out of reach of just about everyone since at the moment, the knock modules are something of a black box, not to mention the skill required.

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There are interesting discussions about how to do this reasonably well with budget tools. I believe there was a great thread on thirdgen.org. When you consider the aftermarket uses the same sensor for several different engines it seems like it would be easy to make an improvement.

Technology has changed so much over the years. Are there any aftermarket systems that monitor spark energy and pattern to determine knock? I could often see it on an analog oscilloscope.

I bought a stand alone system out of Iceland for the Toyota- which at the time didn't offer knock, for an extra $200 now you purchase an option which includes WB and knock- have to force knock on a dyno to tune. This is off my topic tho, I tested the oem ESC module on the Chev and it was the same if not a little more sensitive, not sure I want to purchase the matching knock sensor- both applications are 350cid one is a 85 Corvette TPI (BLH) and one is 89 K1500 TBI.

Just remember that the sensor and the module are two totally different things. I'm not suggesting you need to do anything with the sensor. But if you want the existing EFI to do knock retard like factory, then the knock module is what you have to adjust, and all it does is pull a line low to tell the ECM/PCM when it thinks knock is occurring. Sounds simple in theory, but when we don't know the pinouts for the module and have to account for how much knock to report and when, things get tricky.

There are absolutely other ways of doing it. It's ultimately only if you want to use factory hardware that you end up in the situation where you would need to create your own custom knock module.

There are absolutely other ways of doing it. It's ultimately only if you want to use factory hardware that you end up in the situation where you would need to create your own custom knock module.

And there is the rub- the engine is far from factory- and relatively noisy, so the knock system is not that useful.

As an aside, engine was intended to be 9.5:1 modeled after vortec with AFR head/FIRST TPI, have been trying to tune to 87 octane- I have a few avenues left to try but have audible ping in certain areas. Where do you give up and move up in octane?

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I have a few avenues left to try but have audible ping in certain areas. Where do you give up and move up in octane?

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After failing to reduce knock by adding 1oz MEK per gallon to your 87 octane fuel. :-)

This is an EBL setup, and the ping has been an issue for some time. I dabble in tuning so don't really know it well. I was thinking last night that the learns is doing its thing, I've cut PE/SA to 0, I've taken 5 deg out universally and although it clears up most of the knock table it will still ping in a certain area even with 0 timing. I've filled up it up with better octane and the same thing. So I'm thinking it's going lean under heavy throttle and options are PE, AE, or VE adjustments. This is a 383 sbc with modern alum heads and a version of tpi- so I'm also thinking the tuned ram is really doing something.

In order to stop kock the KS system will reduce spark advance when knock is detected then advance spark back to the ECM desired timing while knock is not occurring. If knock occurrs at any time then spark advance will again be reduced. In order to ensure effectiveness I would look at the kock and spark advance during knock to ensure the minimum allowed advance is not too high. If spark advance cannot be reduced enough then knocking will not stop. I would then look at the initial retard when knock occurrs and the rate at which the system returns advance.

And I wouldn't be afraid to add MEK. :)

Attachment 16088Attachment 16089

I have been looking at the knock module from various LT1 and V6 applications in the late '90s. The circuit is housed in a plastic carrier with eight contacts. Inside there is a hybrid circuit (I believe it is thin film). On the circuit are a number of capacitors (one looks to be a larger polarized tantalum cap), LASER trimmed resistors and two ICs. One of the integrated circuits is a soic 8 pin manufactured by philips (marked NE532D dual op-amp [edit]) the other has a higher pin count (perhaps 16 pin) and is not packaged. The second chip has no markings because it is not packaged. I believe the part is made with solder bumps and is mounted directly on the substrate.

I find it interesting that when manufactured, the hybrid is mounted in the top of the plastic housing with some very low density elastomer. This material is very soft and I believe is used as a sound deadener to prevent flexing of the substrate from becoming microphonic. That is to say that the module could under some circumstance pick up vibrations and turn them into unwanted signal.

I plan to look at this module in the future & try to find it's operation, but for now this is all I have found.

One question for the group... knock is when the compression cycle heats the mixture to the point where it ignites before the spark (pre-ignition). How does retarding the spark seek to cure this? I can see how making the mixture richer might cool things. Overall retarding the timing would cool things when knock isn't present. Perhaps someone could explain?

-Tom

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Originally Posted by Tom H

One question for the group... knock is when the compression cycle heats the mixture to the point where it ignites before the spark (pre-ignition). How does retarding the spark seek to cure this? I can see how making the mixture richer might cool things. Overall retarding the timing would cool things when knock isn't present. Perhaps someone could explain?

-Tom

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Pre-ignition (ignition before spark) and "Knock" Detonation (after ignition) are two different events.

I think the trick is to prevent rather than recover. I did order the sensor, I just found it odd that the same style and engine displacement demanded a different part number.

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Originally Posted by brian617

Pre-ignition (ignition before spark) and "Knock" Detonation (after ignition) are two different events.

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I understand a little more now... with knock the plug ignites the mixture and a flame front starts from it's tip. Normal ignition the front continues, pressure builds and all is good. With Knock what happens next. Could someone point to a good link that describes all this??

-Tom

Pre-ignition is when the electrical spark is not the start of the flame front. It often but not quite always leads to knock. Even if it somehow is not knock is still bad because pressure builds before the piston is ready to convert the pressure to useful work.

Knock is a sudden explosion - detonation - rather than a smooth controlled burn. Instead of building, pressure spikes so fast it's like a hammer striking the piston or the cylinder or the valves.

Depending on the amount of air & fuel involved in the knock event as well as when it occurs, has an effect on its acoustics, but it always sounds like some kind of metal on metal.

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Originally Posted by LeMarky Dissod

Knock is a sudden explosion - detonation - rather than a smooth controlled burn. Instead of building, pressure spikes so fast it's like a hammer striking the piston or the cylinder or the valves.

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Using this definition, knock isn't a result of the spark timing. How does retarding spark eliminate the knock?

I am interested in this because of some other info I came across. Some early aviation engines with turbos and so on had problems with knock. In some cases, this was cured by injecting a water/alcohol mix. In my PCM code I can see where spark retard is applied... wondering if one of the un-used outputs can be used to signal an external pump to inject water. I think this sort of setup would be quite easy in terms of setting up the pump and so on. Software would also be quite easy. Question comes as to how much to inject. This is where things get complicated.. Probably a constant pressure with some sort of jet to control the flow. Just thinking out loud.
-Tom

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Originally Posted by Tom H

Using this definition, knock isn't a result of the spark timing. How does retarding spark eliminate the knock?

I am interested in this because of some other info I came across. Some early aviation engines with turbos and so on had problems with knock. In some cases, this was cured by injecting a water/alcohol mix. In my PCM code I can see where spark retard is applied … wondering if one of the un-used outputs can be used to signal an external pump to inject water. I think this sort of setup would be quite easy in terms of setting up the pump and so on. Software would also be quite easy. Question comes as to how much to inject. This is where things get complicated. Probably a constant pressure with some sort of jet to control the flow. Just thinking out loud.

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Using this definition, knock isn't NECESSARILY a result of spark timing.

Less-than-ideal timing - like, say, the factory spark timing maps we tend to improve on - does not cause knock in and of itself.
Some engines, regardless of timing, are very resistant to knock, whereas others are much less so.

Anyway, did you mean something like the BMW M4 GTS' water injection system?
https://www.bmw-m.com/en/topics/maga...00-horses.html

It's blatantly obvious how old this idea is.

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Originally Posted by LeMarky Dissod

Anyway, did you mean something like the BMW M4 GTS' water injection system?
https://www.bmw-m.com/en/topics/maga...00-horses.html

It's blatantly obvious how old this idea is.

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Thank you for the info & link.

-Tom

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Originally Posted by dfarr67

I did order the sensor, I just found it odd that the same style and engine displacement demanded a different part number.

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The sensor will be a different part number depending on whether it's OBDI or OBDII, because the OBDI version contains a resistor inline that the PCM uses to determine whether the sensor is physically present or not (but that can become damaged and fail without necessarily causing the sensor to fail, tripping a DTC when the system is in fact still functioning as designed). The OBDII version has no such resistor because the PCM determines whether the sensors are present based on their actual output signal.

The modules all have totally different part numbers because every single one is calibrated differently due to changes in packaging between various different engine configurations and vehicle layouts, which cause changes in the audio profile that need to be filtered in different ways. It's this part that is so tricky when you start making changes to the system, and why creating a replacement module would be the only "correct" way to fix the problem of not correcting detecting knock once you've created an engine that doesn't fit the stock GM profiles.

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Knock is a sudden explosion - detonation - rather than a smooth controlled burn. Instead of building, pressure spikes so fast it's like a hammer striking the piston or the cylinder or the valves.

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Knock is the audible side effect of pressure increasing rapidly while the crank and piston are not in a position to be driven by the force created by combustion.

Ultimately the game is to create pressure on the piston while the crank angle is optimum for creating motion from that pressure. It's a bit of a guessing game, but generally your fuel will burn at a rate that will allow you to time the beginning of combustion so peak combustion pressure occurs at or near optimum crank angle. If pressure is created at the wrong time, generally when the crank is not far enough ATDC, continued combustion will create sound and heat energy rather than motion. Pressure can be created at the wrong crank angle by beginning spark too early for the fuel's rate of combustion. It can also be created by altering the rate of combustion through temperature change, by using fuel more likely to self ignite, or by a point or points of high temperature in the chamber causing multiple flame fronts.

Retarding spark timing delays the beginning of combustion and will hopefully delay the onset of peak pressure. When spark is retarded as a result of knock it is hoped the crank angle is great enough ATDC to be drawing the piston away from compression, so combustion pressure is able to act on the piston to create movement. It is hoped during this time that the cooling system will draw heat from the combustion chamber which can help reduce the likelihood of continued combustion problems.

The ESC system is an active system which has the ability to delay onset of combustion in response to audible knock. The GM implementation will significantly delay combustion then begin to reduce the delay over time. If knock is detected the cycle of delay then reduce delay will repeat.

Water injection helps prevent knock by slowing combustion. Rather than delay the beginning of the combustion event, WI delays the onset of peak combustion pressure. WI can be very effective as liquid water draws heat energy from the chamber in order to convert to steam, and steam slows combustion.

Alcohol is sometimes added to water or injected by itself. Alcohol is more combustible than water but has a higher octane rating than most gasoline. In cases where combustion temperature is triggering fuel self-ignition, increasing the octane rating can help. Additionally liquid or vapor alcohol, like water, will draw heat from the chamber in order to change to gaseous form. This method also delays onset of peak pressure without delaying the start of combustion.

Fuel additives such as Methyl Ethyl Keytone, alcohol, and others attempt to increase the octane rating, the fuel's resistance to self-ignition. Additives generally work in the same way as alcohol above.

Ultimately you will lose more power when using ESC with very conservative settings. Upon detecting knock, combustion start is delayed, often far beyond what is needed to create peak pressure at optimum crank angle. As the system reduces the delay, it is possible for excess heat in the chamber to cause knock to occur again which triggers increased delay. Preventing knock in the first place generally means excess heat will not be created in the chamber so spark does not need to be delayed.

Excellent explanation Shannen :) One note discussed briefly earlier is detonation and pre-ignition are two different things. Pre-ignition can be fatal to an engine VERY rapidly.

So I went back to the BLH ESC module (1985ish Corvette app) and installed the new matching knock sensor (both applications OBD1). Still showing knock but I'm comfortable with working with this. To start found out my AE/injector settings were not updated after an injector change from Bosch 3 to 4 and probably creating a lean condition in high demand areas.

Some more from b&g site

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Question: What is detonation, and how can it be controlled?

Answer: Detonation is often referred to as engine knock. This condition occurs when fuel ignites early i.e. before the piston reaches the position where the spark ignition is scheduled. This means that the ignition explosion is trying to expand a cylinder chamber that is shrinking in size. When this firing pattern occurs it attempts to reverse the direction of the piston and the engine. When detonation occurs, the internal pneumatic forces of the piston can actually exceed 10x the normal forces acting upon a properly timed high performance engine. Early detonation is generally caused by excessive heat, extreme cylinder pressure, improper timing of the ignition system, inadequate fuel octane rating or a combination of these factors.
The most common factor that causes engine knock is excessive heat. Additional heat is produced in an engine as it generates an increased quantity of power. Today’s pump gas only tolerates a finite amount of heat before it ignites. If this measure of heat is reached too early in the engine cycle it causes detonation. Although adding a supercharger to an engine rarely causes detonation it does create additional heat. A forced induction engine actually produces far less heat than a comparable normally aspirated high compression engine. To address the issue of increased heat an intercooler may be added to the supercharger system. An intercooler is a natural solution for forced induction and is included in many supercharger kits on the market today.
For engines currently experiencing detonation problems, the addition of an ignition/timing retard system, the use of higher octane fuel, or the addition of an intercooling solution may be used to address the issue. Ignition retard systems can be helpful in certain situations, but can greatly reduce the horsepower output of an engine. Any reduction in timing reduces horsepower. Reduction in timing can save a motor from detonation, but the excessive heat which was causing the detonation is still present. Intercooling is a more desirable option in most cases because it actually removes the heat which causes detonation, and allows higher boost levels to be safely run with full timing on pump gas. This setup produces the maximum benefit in terms of horsepower gains and engine protection, many times without additional maintenance or hassles.

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To start found out my AE/injector settings were not updated after an injector change from Bosch 3 to 4 and probably creating a lean condition in high demand areas.

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AE typically only comes into play for a very short time. The job of AE is to keep the cylinder charge from going lean until the VE delivery "catches up." Lean AE settings could start the "knock chain" when the throttle is opened quickly but generally knock during extended load are not due to AE issues.