EcuTek and Knock Detection: Is your engine knocking?
 

So I haven't seen any real in depth discussions about engine knock and the VQ37VHR on here and have only seen it discussed really briefly on the 370z forums. Specifically regarding EcuTek Software and how it reads the input from the knock sensors on our engines.


So as I've been e-tuning my car with OVT, I've been opening the logs trying to get a better understanding of what is changing between files, what my engine is doing, and overall understanding of tuning.

As I was doing so I came across knock sensor readings in the logs and was a little concerning because I was seeing many changes in numbers higher in the rev range. The problem is, there doesn't seem to be any pattern and the values appear to just be a arbitrary number :dunno: that the sensor is hearing. As I dug deeper there appeared to be number changes under load (WOT), after letting off the throttle, and shifting gears (I'll discuss this later).

Below is knock sensor readings from a WOT run that I made on the latest file revision.

https://cimg4.ibsrv.net/gimg/www.myg...665e0b7eb2.png

As you can see the values are all over the place, but from what I understand negative=bad and positive=correction. What I don't understand is why they appear to be random as the engine becomes more active.

And as you can see below, I pulled a log from my sedan.

https://cimg5.ibsrv.net/gimg/www.myg...413326fce6.png

Smaller numbers due to lighter engine load, but also seemingly random.

I've read into this and found that false knock (phantom knock, or spooky knock as I would like to call it) is potentially what is going on here. My tuner thinks so as well and stated that G's of my mileage (85K) and age CAN develop somewhat noisy drivetrains. He says that because the rest of the log values (AFR, Engine data, Ignition timing and correction, VVEL) all look good.

Given that VQ37VHR knock sensors are essentially mics listening for knock (better visualized below IMO) it does make sense that the sensors could be hearing drivetrain noise as knock and correction (?) and that's the values I'm seeing.

https://cimg5.ibsrv.net/gimg/www.myg...c341414fef.png

Now, all of that being said. I still don't think that these values are degrees of knock and correction (-16 and +50 at the extremes). That would be seemingly impossible, and from what I read would not look the way it does. It should look like a stair step as the engine over-corrects and reintroduces timing. I also had him enable the RaceRom feature of knock warning which flashes your check engine when knock greater than 3 degrees is detected. With this I was able to replicate "knock" under some of the conditions I spoke about prior and when/where they would be located in the logs to some degree.

My questions are?

1. What are these values being read from the sensors in EcuTek
2. Does anyone have "No knock" and "Finished" file logs to compare against to see if there is any trends?
3. What do you make of this?

Anyone is free to chime in with findings or understandings greater than mine.

Furthering my tuner's theory that the ECU is probably picking up drivetrain noise, I am getting CEL flashes at low speed and engine load, low engine load shifts, and at seemingly random high engine load shifts.

Are VQ knock sensors this sensitive?

If your CEL is flashing, you have pre-ignition and that is very hard on the pistons and rings. Knock sensors are designed to more sensitive to the frequency of the sound of pre-ignition, but other sounds in that same frequency can be falsely detected as knock.

Log and post your engine RPM, ignition timing, air intake temp, measured AFR, intake manifold vacuum and absolute engine load at wide open throttle in second gear from about 2,000 to 7,500 RPM.

I suspect your tune might be a little too aggressive for your driving/environmental conditions. Hot weather requires a slightly richer AFR to help cool the combustion chamber to prevent pre-ignition. A richer AFR requires MORE timing advance due to the slower frame front.

Pre-ignition is not detonation. Detonation is "knock", the uncontrolled burning of end gas in the cylinder. Pre-ignition is the result of very lean combustion causing the spark plugs and other protuberances in the cylinder getting extremely hot, hot enough to ignite cylinder charge before the spark plug fires.

Pre-ignition = before plugs fire.
Detonation = after plugs fire.

The CEL is flashing because of the RaceRom feature of EcuTek tunes. It's hijacking the CEL to show when the sensors are "hearing knock".

The wide open throttle logs I posted first are snips of just engine speed and knock sensors. The logs are recording about 25 other values including AFR, manifold absolute pressure, and intake temps, on both banks. The knocks don't seem to have any correlation with AFR much since I'm running between 11.91 (target) and 12.10 at WOT throughout the rev range with very cool air at the time of the log. That's why I'm not so sure it's knock. I'm seeing the same pattern over two vehicles with similar age, miles, and conditions. And the conditions that I'm seeing it in aren't really conducive for knock.

I'll post whole logs when I can

Here is the upper portion of the log, directly above the knock sensor readings.

The blue square is where the snip I took begins in the original post.

The gear always states (1) because its the 7AT. It does not change.

https://cimg9.ibsrv.net/gimg/www.myg...c114080898.png

It does not appear to be leaning out where there is knock, air intake temps are consistently 77F (25C), engine temps are normal.

Don't use 1st for your log. Run either 3rd or 4th for a more accurate picture. Also allow your coolant temps to reach 180ish.

I forgot to state all WOT logs I do are 3rd gear. 4th pulls to redline are triple digit speed territory, unfortunately lol. It displays (1) for every gear :dunno:

Coolant is displayed in C, so the temps are ~183F-ish if I'm not mistaken.

If you look at your ignition correction, it's pulling timing. There's a built-in "safety" which triggers this. Phantom knock is very real, I dealt with it often when tuning turbocharged rotary engines. Generally speaking, if it's an isolated one-off reading, it's phantom. If it has a value slope to it, it's knock and something is amiss.

I purposely did not look at my logs due to my tuning background and not wanting to second guess someone who has far more experience with the VQ than myself (as well as the advanced EcuTek tuning software). With that said, I'm assuming your tuner DOES have lot of experience with the VQ and therefore knows you're within safe parameters in your current state of tune. Engine condition can force the tune outside the safe parameter. The VQ is noisy as it approaches redline. I'd examine oil brand, plugs, (hell, even motor mounts) anything that could return your car to more favorable OEM parameters.

Edit. It's crucial you know at what knock reading threshold the car pulls timing. It was "normal" on the cars I tuned to see knock readings from 40-80 on the ECU system I was using (turbocharged rotaries) and that was perfectly within the realm of safe.

Knock sensors can always be amiss but you have the data from all six cylinders and it's pretty similar. Your tuner could always pull 10 degrees of timing across the board and add 5% fuel and see what happens to knock readings.

Overly rich tuning can also cause phantom readings with excess fuel igniting in the exhaust manifolds.

I'll try to take some knock readings on my car tomorrow, it's hot as f*ck here currently and I have a hot and "not as hot" map.

I inadvertently requested what you suggested preemptively lol. I had him pull timing a bit, he said since I'm running a bit rich anyway, it should help quite a bit. Since then, I'm seeing less knock events up high and down low (accelerating, not WOT). But I'm still seeing the most right around 4k rpm under load and at WOT. It's almost like a sound resonance thing since by all other measure and readings, it shouldn't be knocking, yet that's where I'm seeing it the most.

He also said that since we were seeing excessive knock he enabled full knock listening. Stock and RaceRom cars alike disable knock listening down low, normally. Since my car is always listening, I'm seeing more down low.

Just got tuned with ecutek yesterday. Topic of knocking actually came up and I asked about it briefly. Sebastian at Specialty Z said that the knock sensor is set to pick up sounds at a specific frequency. Said he heard a tiny bit of knocking on low rpm in my car so he tuned the air/fuel ratio to be slightly richer.

MORE DATA!!!

So. Weird findings.

After having my tuner pull some timing, I was still seeing some knock. BUT I also added some Lucas Octane booster which boosts the Octane of my 93 up to around 102+, essentially making it race gas. Now, initially I was getting less CEL flashes (EcuTek Knock Warning). But I pulled up the logs and they look THE SAME.

The same patterns.
The same knock sensor value range (-1 to -16) on all cylinders.
The same behavior.
Less CEL Flashes????

I'd love for some tuners to chime in. I want to get to the bottom of this, so down the rabbit hole we go!

That stuff only boosts about 1 octane point

I used a whole bottle on half a tank. It's meant to treat 25 gal. It's more than a point lol

Octane boosters you buy at your local auto store are like lubricants for your muffler bearings. There have been plenty of tests showing they only raise octane rating about 1-2 points at best. If you really want to bump it mix a gallon of e85 in a full tank of gas