Some standalone ECUs (eg Haltech Elite 750, DTA T2 & T4, MS2, MS3) and many piggyback ECUs (eg AEM FIC8 etc) do not have a dedicated knock sensor input. There are two ways to upgrade these ECUs to have some sort of knock input.
Knock Input Upgrade – The Options
Which option depends on the type of knock sensor that is used.
The first is to use a resonant type knock sensor that is tuned to the knock frequency of the engine the ECU is being used on. The OEM knock sensor is the obvious first place to look, if it’s a resonant type knock sensor it should be possible to use it & give some sort of knock signal to the ECU. Simply wire the sensor to the analog input on the ECU. Set a threshold intensity for the knock signal and retard ignition/add fuel. If the threshold can be set according to RPM it is a bonus although it may be possible to getaway without setting a threshold against RPM.
The second option is the use a dedicated knock sensor controller which can be used with a non resonant knock sensor/wide band knock sensor. With this solution the target frequency can be selected, the controller can be programmed to output a knock signal to the ECU under the conditions we chose. Click this link for a list of knock sensor systems and their features together which features are most desirable. You should be able to make a more informed decision as to what types of knock sensor suits your requirements and budget.
Is it better to get an ECU with integrated knock detection?
The only reasons I can think not to, is if you believe the knock detection capabilities of your chosen ECU is not good enough for your requirements.
Another reason (which is connected to the first) is that you do not like the way in which the knock thresholds are setup in the software of your chosen ECU. eg its far too complicated, you can’t set it up how you want etc
Yet another reason would be you already have a standalone ECU or a piggyback ECU and you do not want to buy a another ECU if you can get a separate box for much less money.
Benefits of integrated knock detection
Less wiring. This can be a big plus. You do not need to run extra power wires and signal wires you just need to run the knock sensor signal wires into the ECU and you are ready to start setting up your knock thresholds.
Mapping. You do not need to set up maps in two different ECUs eg setting up the knock sensor controller and its outputs and then setting up your engine ECU to respond in the way you need given the signal from the knock sensor controller. You can do it in one go and you don’t have to use two different types of software.
How To Decide
How do you decide which is the best route to go down?
I think budget will probably be the driving factor for a lot of people. If you have unlimited budget I would get the integrated solution all day long. (Assuming I am happy with the knock sensing capabilities of the engine ECU I like).
If budget is a consideration, add up the cost of the separate knock sensor system and minus that from the cost of your ideal-world engine ECU. Is the difference in price worth the extra installation and setup convenience?
You already have a knock sensing solution integrated into your existing ECU and you want to buy a separate unit to compare the performance of the two solutions and/or evaluate how well you have your knock detection strategy set up in your engine ECU/knock sensor controller. Is one system picking up knock the other is not? Is one system picking up phantom signals? and so on.
Wrap Up – Knock Input Upgrade
It’s possible to add knock input functionality to an ECU which does not have dedicated knock detection circuitry for minimal outlay. Simply use a resonant type knock sensor if you can find one.
If you want more sophistication it is possible to buy external products which can output a signal to your ECU under the conditions you chose. You do not necessarily need to buy the high-end standalone ECU offering, to get knock detection functionality although there are many benefits in doing so.