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Discussion and questions related to the course Practical Reflash Tuning
I've just tuned my buddies evo X, the bottom end of the engine is forged and it has an upgraded Garret GTX3071R turbo.
I am using ECU Edit for the tuning and the car is on 95 RON fuel.
I am using a plex knock monitor v2 for knock detection, the sensor is mounted on the engine head. I am a novice tuner and I am really having difficulty discerning what is normal engine noise and what is knock through the headphones. As such I am using the plex with a rpm input from the engine and looking at the engine noise vs rpm profile on the laptop with the plex software. I set my threshold and basically just used this alone (no audio) to know if the engine was knocking or not.
Bottom line, as I increased the timing and the engine made power the evo ecu was seeing more and more knock count but I was not seeing any knock on my noise vs rpm plot from the plex (or so I think). I ended up adjusting the knock table threshold in the ecu to tell the evo ecu that what it was seeing was not real knock, but I found I had to raise the table quite a lot.
The engine is still only on waste gate spring pressure at 15psi which has me thinking why would the threshold need moving so much in the evo ecu.....is the engine really knocking or am I just paranoid?? Some help would be appreciated....can also upload the map on request.
I know the engine is forged and this could affect the engines noise profile vs stock but again....I found I had to move the stock knock table quite a bit.
Think about the big picture of knock detection. Detecting severe knock is easy, because you will hear it rattling with the naked ear; so is detecting zero knock, for the most part (it's not going to knock at idle unless something crazy is going on). It's that borderline area that is tricky. Ask 3 different tuners where the knock limit is and you get 3 different answers. Not only that, but the method of detection can vary - some use actual microphones, some use simpler methods like pipes/cans/etc, and if you have the equipment you can even look at cylinder pressure.
Now where exactly did you add the sensor? I don't know off the top of my head where the stock 4B11T sensor is, but on the 4G63 it's dead in the middle of the block (you can Google that and pics will pop right up). Usually on an I4 engine if there is only 1 knock sensor the best place is right in the middle, as long as the signal gains are tuned carefully. If you start putting that sensor wherever you can fit it you can end up unable to detect knock on 1 or more cylinders. The ribbing and material of the block can deteriorate the signal on some cylinders, or you can pick up extra noise due to something like the accessory drive. The newest I4 engines (BMW N20 or B48 for example) tend to have two knock sensors, one between No 1&2 and one between No 3&4 in the block. If the sensor is towards the #1 cylinder, it could be completely blind to knock on the #4 for example.
Let's put it this way. There's a good chance the stock knock sensor is in a better location than wherever you put yours. BUT the modifications you made to the engine may have affected the knock sensing, making phantom noise and causing it to be overactive. Given a choice, I would NOT trust your aftermarket knock detection system and questionable sensor placement over the stock system, unless you have an experienced and trained ear for knock and trust that judgment above all else. If someone who tunes Evos all the time can physically get in there and assess it that would be one thing, but right now the safest thing to do is put the knock thresholds back to stock and let the ECU do its thing. Remember, a mistake with knock control could be very costly.
Of course you could remove the stock knock sensor completely and replace it with your sensor, and then lose knock retard capability of the stock ECU. That's risky. You better have a really solid tune and good temperature related spark compensation tables. I know some will recommend you sort of "stack" the sensor on top of the stock one, but there's no telling how much that would impact the signal.
If you really want to reduce the sensitivity of the stock knock control system, do it in a very small increment, enough to effectively advance timing a degree or so. If you find yourself wanting to disable the stock knock control system to agree with your aftermarket system, ask yourself if that's a risk you want to take. What if the stock system has better signal processing than your Plex? What if the stock sensor can read all the cylinders and your Plex can only detect 2 or 3 cylinders? You only have to blow one cylinder up...
Thanks for the response and point taken. The sensor placement is not ideal as you said but it's the same point Andre uses when he's tuned evo X's in the past (I've asked on here about that in the past).
If possible I'd like someone with some more experience with the Plex to respond , is it possible that my rpm Vs noise threshold can look clean but the engine could really be knocking? I am using the Plex in knock mode 2 (second harmonic) due to the less than ideal sensor placement .
As I said...above 5000rpm I had to increase the evo X knock threshold tables by large amounts because the Plex graph looked clean. I adjusted timing and both mivec intake and mivec exhaust maps and was able to pick up power on all three....each time the engine made more power the evo ECU registered more and more knock counts but the Plex kept showing a clean graph with the occasional knock (1-2 counts).
@Chris1388 I have used the cylinder head on the 4B11 in the past but I also could audibly pick up knock relatively easily to confirm that I could distinguish knock from background noise. Have you purposely tried inducing knock at light load and low rpm to see what the Plex sounds like and what the graphical logging shows? I'd be very cautious until you've actually proven the system CAN detect knock before you rely on it. If you're really struggling to hear knock then I'd also try and get the knock sensor onto the block. I know this is a PITA on an EVO X but it will be time and effort well spent if it saves an engine!
Hi it's really not such a big deal to mount the knock sensor on the Evo X. below the intake manifold there is a gold bracket mounted to the block to hold the harness, just remove it and mount the knock sensor there. Use 3/8 wrench tools with a universal joint. This is a 10min job!
I found the EVO X knock detection very accurate on stock blocks, but I don't have experience on built blocks.
What filter frequency do you use on the Plex?
I am using 85mm on second harmonic.
What are you using for the audio filter ?
I'm using usually a filter between 6-7hz.
I found on most engines non audio filtering works best and is the easiest to distinguish knock from background noises.
I don't recommend to use just the display on the plex. Sometimes you hear knock and the plex display doesn't show a peak.
You have to intruce knock several time and try different filters. You can also use the knock audio function with FFT ANALYSIS in the PC LINK Software to find knock frequenty. Also if you don't have a LINK ECU.
Andre I've not tried purposefully inducing but from the responses I've got I'm guessing I'd have to overcome my fear and do that. What rpm and load should I do this at? Should I do it in boost or vacuum? The car is on 95ron fuel and is running 15psi on waste gate spring pressure. Full boost comes in at 4000rpm.
I would start with inducing knock at a lower engine speed and lower load (ie less risky condition).
I'm wondering if it would knock at lower load and rpm....the stock map is already at 35-40 degrees in those areas
Guys see attached a picture of my rpm Vs noise profile from my plex....let me know what you think. There is also a picture with the settings I am using.
It's the right basic shape. Have you induced knock yet?
Well while tuning and advancing the ignition timing I have seen instances where points have gone over my threshold and I deemed it to be knock and then removed timing and it went away but as for detecting it with my ears I find it very, very difficult ....I don't know if it's this engine or not but it's definitely not night and day as I've heard others speak about the Plex.
I will try adding timing and low load and light rpm and purposefully try to induce knock and play with the filters, but to be honest I don't like the idea making the engine knock over and over while I play with filters to see which sounds the cleanest....I've tried a couple and I can't hear anything different from the increasing noise level I hear through the headphones.....for the money spent on the Plex I thought it would be easier than this