Mitsubishi 3000GT & Dodge Stealth Forum banner

Better, faster safer knock detection?

2K views 6 replies 4 participants last post by  OldMadBrit 
#1 ·
Having blown one motor up with a failed knock sensor and being painfully aware of the limitations of knock sensors/knock sensor calibration, I just came across a really interesting factoid - modern control systems use "ion-sensing" in the flame front for real time knock sensing.

This looks to be vastly superior to our knock sensors. Much less prone to calibration error and closer to real time. At first take, it looks like this could be built into a sequential COP kit. I think it would need a dedicated board to generate a knock signal for a Chrome or AEM V2 ecu, but later stuff like the Haltech may already have options for this.

I saw this write-up on the Aprilia forum:

Ion Sensing Ignition Systems
Ion sensing systems are based on the principle that electrical current flow in an ionized gas is proportional to the flame electrical conductivity. In other words, by measuring the current flow in the post combustion ion trail between the plug electrodes, engineers can get an idea of the combustion efficiency during combustion itself. This turns the spark plug into an intrusive engine sensor, providing real time information on each cylinder's unique needs.



Originally, ion sensing ignition systems were used primarily for knock detection and misfire detection. Knock creates a pressure oscillation in the combustion chamber that is reflected in the current measurement. It is more sensitive than conventional knock sensors and eliminates the need for the additional sensor(s). In the presence of a misfire, no ions are created and there is no current flow that can be easily detected. Ion sensing misfire detection is more stable and more accurate than the more common method of monitoring crankshaft speed fluctuations.

@Unlogic @familyMAN @RealMcCoy @Chris @ Rvenge Performance @bboyalan
 
See less See more
1
#2 · (Edited)
It's nothing new, SAAB has been doing it since the 90's.

I guess as it becomes more mainstream, it'll become a thing in the aftermarket world. At this stage, no one's interested as far as I'm aware. I certainly haven't heard anything in the LinkECU circles, no doubt there's work being done behind the scenes.

The factory knock detection system is excellent if it's working properly, if it's paired to an LCDBC you can't go wrong and you'll know exactly when it's broken.

Bosch donut knock sensors work well with aftermarket ECUs but they've got to be set up correctly, it took me weeks to get the knock detection dialled in on my LinkECU.....no wonder most tuners can't be bothered. Of course, you still need a datalogger or some kind of visual/audible indication so you know it's stopped working.
 
#3 ·
Steve is using an AEM EMS Series 2. His options for easy viewing include an older serial data gauge, CAN gauge e.g. AEMnet, or a digital dash display.

RE sensor: bit overkill and unnecessary, IMO... especially since you are on pump gasoline. Safe tune with tight knock cal are adequate. If anything, you should be looking at an incorporated fail-safe(s) for your WMI i.e. flow monitoring. You currently only have lean-out and knock for that.

-sent from my Galaxy S22 Ultra
 
#5 ·
I find that the knock detection in stock ECU/Chrome is superior to the common aftermarket AEM1/AEM2 ECU's. My guess is that this boils down to the filter circuitry in the stock ECU and it's related software calibration which is done each time the car is started.

If you run a stock ECU and let the ECU control the boost (instead of running a boost controller) you will feel the car pulling boost and timing long before you hear any knock. But as many people don't have the patience to setup the stock ECU boost control tables and run a "cool" aftermarket boost controllers instead they miss out on this and leave the ECU only with the ability to pull some timing.

I know that Motec ECU's have good knock detection support but it requires proper calibration which is both hard and scary to do since you have to provoke knock in order to log it properly so that it can later be analyzed.
 
#7 ·
IMHO, vibration/acoustic based knock sensors (like our OEM) have a fundamental limitation, based on noise to signal ratio. With this type of sensor, there is always a compromise between filtering out noise from other engine vibrations v missing knock count. As a result, there is a better than even probability that the engine is experiencing multiple knock events before the ECU recognizes it. Every knock event induces some level of damage - and damage accumulates.

I knew that more modern turbo motors were using something better. We saw OEMs make a big jump in stock boost from ~11psi in the 90's to >21psi now - and in the meantime the gas got worse.
I was initially surprised to learn that they are using this methodology. However, it makes a lot of sense because fundamentally it should have a much lower noise to signal ratio - there isn't anything else to create the same charge transport conditions in the ion stream as knock.

This is now standard across high performance motorcycle motors. Both my Aprilia Tuono V4F and my Yamaha R1M use it. I guess it's part of why they can run beyond 13,000RPM with 13:1 and higher compression ratios on shit pump gas all day long.
 
#6 ·
Nah, stock is slow as balls in comparison lol 😆 IMO of course. It is simple... run a tight knock cal AND enable knock per cyl, if applicable. This is even better with dual WB (one per bank) for precision. Adjust as needed/wanted based on data+conditions to aggressively affect fuel and ignition if that concerned.

There is only so much preventative and safety stuff that can be done. If something is going to break or go out, then it is sometimes unavoidable especially if mechanical or electrical.

-sent from my Galaxy S22 Ultra
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top