MartinS Posted February 4, 2023 Report Share Posted February 4, 2023 Hi, I have some confusion about filter choice for knock tuning my Subaru EZ36. I used the formula for Knock Resonant Frequency=1800/3.14*piston diameter(mm) So with an engine bore of 92mm (very close to piston diameter) I get a Knock Resonant frequency of 6.23 kHz. Should I go straight to that setting of 6 kHz or is it better to start with a wider freq band for setup and go to 6 kHz when all the levels are set? Quote Link to comment Share on other sites More sharing options...
Adamw Posted February 5, 2023 Report Share Posted February 5, 2023 Set it to 6KHz narrow initially and if you get lots of random knock level spikes that arent related to knock then try something different. The calculated frequency is not always useful. Quote Link to comment Share on other sites More sharing options...
MartinS Posted February 7, 2023 Author Report Share Posted February 7, 2023 Started the process, set at 6 KHz narrow and 0 deg ign retard, gain channel 1. When running at 4000 RPM in neutral, there was a very large difference between cylinders so I used the individual cylinder gain channels to balance them out so they are now set at 0.6, 1.1, 1.1, 0.4, 0.9, 0.8 for cylinders 1-6 respectively. At 4000 RPM no load I now get a global knock level of approx 40-45 with a little jumping around but mostly 30-50 range showing up for each cylinder looking fairly uniform across all 6. When I do a WOT run in 3rd gear from 1500 to 5500 RPM, from 4000 and up, the global knock count quickly approaches 700-900 and starts flashing 1000's as RPM increases closer to 5000. Jumps around a bit but not a huge amount. I tried decreasing the gain channel to <1 but it always defaults to 1 (ie, I can't set it to 0.5 for example). Since number 4 cylinder gain is already down to 0.4, I don't seem to have enough room to go further down there. I can't see how to get the global knock to decrease below 1000 even without the 20% headroom suggested. Also, despite adjusting the individual cylinder gain channels, when looking at the cylinder knock counts in log files, they seem to still show the unadjusted knock numbers for each cylinder. Am I missing something? Quote Link to comment Share on other sites More sharing options...
Adamw Posted February 7, 2023 Report Share Posted February 7, 2023 16 hours ago, MartinS said: the global knock count quickly approaches 700-900 Knock count or knock level? Knock count is irrelevant, this just means your knock level is exceeding the knock threshold which probably hasnt been tuned yet. Knock level is what you are adjusting with gain. Quote Link to comment Share on other sites More sharing options...
MartinS Posted February 7, 2023 Author Report Share Posted February 7, 2023 sorry, checked what I'm looking at, definitely knock level... Quote Link to comment Share on other sites More sharing options...
Adamw Posted February 7, 2023 Report Share Posted February 7, 2023 Hmm thats very odd. From the sounds of it I suspect your sensor may be a resonant frequency type or possibly it is faulty. Im assuming its mounted in the stock location and not loose or rubbing on the body or anything? Some resonant frequency sensors get very excited around the knock frequency and generate very high amplitude, which can be too high for the ecu inputs even with gains on lowest. There are exceptions to the following rule, but as a general observation, usually most problematic resonant frequency sensors are single wire type and and most 2 wire sensors are usually ok. Pictures on google suggest the EZ36 has a two wire sensor so im not confident if that is the case here or not. I think you will have to try another sensor, preferably a wideband type. You could also try changing the frequency as a resonant type will be much quieter at other frequencies to see if that give an acceptable result. Quote Link to comment Share on other sites More sharing options...
MartinS Posted February 8, 2023 Author Report Share Posted February 8, 2023 You are correct, something is odd. Starting yesterday, when I try and turn on knock control on the ECU, it turns knock off immediately. When I open and download a setup file which has the knock on and set up, the ECU turns it off once downloaded. Is this a wiring or sensor issue? It's kind of strange behaviour as the engine isn't running and when I started the process a few days ago, it seemed to work fine.... Quote Link to comment Share on other sites More sharing options...
Adamw Posted February 8, 2023 Report Share Posted February 8, 2023 Are you on firmware 4.10.2? I vaguely remember the knock turning off after a reset being a bug in old firmware, something to do with you couldnt have DI5 pull-up and knock enabled at the same time. If you are on 4.10 software then attach a copy of your map and I will take a look. This wouldnt have caused the high knock levels however. Quote Link to comment Share on other sites More sharing options...
MartinS Posted February 8, 2023 Author Report Share Posted February 8, 2023 Yup, 4.10.2. I like this explanation better than some of the ones I was thinking of...all of which had me in the garage with a soldering iron for days. Setup file link attached. https://drive.google.com/file/d/1yBqjfvIytquVvQp0zp_5LLi-e46_N2qV/view?usp=sharing I was wondering if choosing the 6 kHz filter was the problem with knock noise but I haven't had a chance to try the 4-10 kHz filter as I can't turn the knock on! Thanks Adam Quote Link to comment Share on other sites More sharing options...
Adamw Posted February 9, 2023 Report Share Posted February 9, 2023 Ok I just played around a bit. I was initially getting the same issue as you with the knock toggling off as soon as you enable it. I think the processor needs a reset before enabling to allocate the tables properly. Here's what I done and it seems to be remaining active now: Connect to ecu, load a fresh copy of your map. Do a store. Power cycle ignition. Connect to ecu, set knock control to internal, do a store. Let me know if that doesnt work for you. Quote Link to comment Share on other sites More sharing options...
MartinS Posted February 9, 2023 Author Report Share Posted February 9, 2023 That worked. Thanks! Wide band filter (4-10 kHz) helped but at 5000RPM still getting flashing at 1000 knock level so better but this somewhat limits my rpm range. Won't be revving the engine that high often but it means power reduction when I need it when really there's no knock or defeat knock control at 4500RPM and have no protection above that... I've dropped the individual cylinder gain channels down another 0.1 so the lowest if 0.3 but haven't tested yet to see if that helps. Can I go as low as 0.1 on the noisy cylinder (actually, 2 noisy cylinders: 1 and 4 are very close to the same low gain and the knock sensors are also mounted closer to that end of the engine so I don't think this is a sensor issue as the one is only a little more sensitive than the other for cylinders 1 and 4) without causing a sensitivity issue? I'm also a little confused in the setup, I get 2 frequency channels, one has an array of choices and I've set wide 4-10 kHz. The other has 4 choices: LP, 5.5, 7, and 9. Help file says these are the same setting for different ECU's but I'm not sure which applies to my ECU. Quote Link to comment Share on other sites More sharing options...
Adamw Posted February 9, 2023 Report Share Posted February 9, 2023 You have an xtreme so the 4 choice frequency menu is the one you use. Reducing the Individual Cyl gain values arent going to solve the problem, these are software gains that adjust the already windowed and processed data. The main Gain channel adjustment is a hardware amplifier on the input side of the dsp. If the amplifier is already on its lowest gain (1.0) but the sensor voltage is so high that it is saturating the dsp input (indicated by the global knock level reaching 1000) then the signal has already been messed up by "clipping", just turning the volume down using software gains after the signal has already been distorted isnt going to give you anything useful. You will need to change to a wideband sensor. Quote Link to comment Share on other sites More sharing options...
MartinS Posted February 10, 2023 Author Report Share Posted February 10, 2023 Ok, I did not see that explanation for some reason. I've been adjusting the wrong channel and didn't understand the main channel is not digital. Kind of how I roll. So, when I looked at the 4 choice channel, it was set to 7 kHz. So it's been there the whole time, no wonder my adjustments did nothing. I calculated I wanted to be a little over 6 so I tried 5.5 and the numbers are very reasonable now knock levels peaking at about 550-600 at 5500 RPM giving me room to add the 20%. I guess there's a lot of noise around 7 kHz. Is this a reasonable solution? When I'm feeling brave one day I'll advance until I get some know to make sure it's sensed... Quote Link to comment Share on other sites More sharing options...
MartinS Posted February 10, 2023 Author Report Share Posted February 10, 2023 Keeps turning itself off. Turned DI5 off as not using speed sensor right now. Still turns itself off. I can do the maneuver you mention but if I don't and drive the van not hooked up to the computer, when I next connect, knock off. Quote Link to comment Share on other sites More sharing options...
Adamw Posted February 10, 2023 Report Share Posted February 10, 2023 I will ask Simon who knows the G4 better than I if he has any thoughts on the knock turning itself off. That will be Mon or Tues. Remind me if I dont reply. Quote Link to comment Share on other sites More sharing options...
MartinS Posted February 19, 2023 Author Report Share Posted February 19, 2023 Hi Adam, any luck on this topic? Quote Link to comment Share on other sites More sharing options...
MartinS Posted March 1, 2023 Author Report Share Posted March 1, 2023 Bump Quote Link to comment Share on other sites More sharing options...
MartinS Posted March 21, 2023 Author Report Share Posted March 21, 2023 Have done more research and trial and error on this and, as you say Adam, if I connect, open current file, save, cycle ignition, then turn knock on it stays on. Well, until I upload any changes to the tuning file in which case it turns itself off again. That's what confused me earlier, it stays on until I upload any changes then it's off and I have to reset as above. Seemed random until I realized the pattern. So, irritating but manageable and I can live with it. Let me know if any solutions to this known. Quote Link to comment Share on other sites More sharing options...
koracing Posted April 5, 2023 Report Share Posted April 5, 2023 On newer ecus if you can't get the gain down far enough to give reasonable numbers, try the 2nd order resonant frequency - or double your first resonant frequency. It should show similar activity but at a lower amplitued. This has worked for me on newer versions of the hardware/software, but I'm unsure of the capabilities on the older G4 platform. Quote Link to comment Share on other sites More sharing options...
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