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As I've been tuning my car, I've noticed some persistent knock counts. Through probably 6-8 iterations of my tune, I've datalogged to find a few scattered knock counts but a significant cluster right around 1250 RPM and 20-30 kPa. Each time I pull some timing in those cells, but it has never gotten rid of the knocks there.
On my last run, the few knocks I normally saw ballooned to a concerning 37 knocks (well, the final tally was 78 but I think there was a communication error with my bluetooth adapter where it rose to 78 at the end) in a 22min log. Interestingly, most of the knocks were in almost a perfect straight line at varying loads at 1250 RPM, as seen below.
Given the clear pattern and the lack of effectiveness of decreasing timing, is it possible that this is caused by transmission noise (I know the black tag ZF6 is known for being noisy at low RPMs) or something else beside my main spark advance table?
Last edited by C4ProjectCar; 06-05-2017 at 02:20 AM.
It is possible that some external issue is being picked up by the knock sensor, check your actual timing that is being commanded in that area and reduce it by a large jump just to see what happens. If you still get knock counts you can probably assume they are false reports and adjust the tune for the false knock.
Ended up having to drop timing quite a lot there (up to 8° in some cells), but I've gotten it to calm down a good bit.
I've noticed, though, that I see knock counts almost exclusively within the first few minutes of driving. Because I'm doing nearly back-to-back runs, my initial coolant temp is almost always above 200° (thermostat is 180°) and I'm in closed loop. With the car already hot and out of open loop, any idea why it would knock more in the beginning? Do the pistons cool down enough in 15min for piston slap to cause false knock?
On another note, is there any reason for me to touch the PE spark advance and closed TPS spark advance tables? I hear people leave PE as it is at 0° for smoother power? And none of my sources mentioned tuning the closed TPS table.
Last edited by C4ProjectCar; 06-05-2017 at 11:05 PM.
Ended up having to drop timing quite a lot there (up to 8° in some cells), but I've gotten it to calm down a good bit.
I've noticed, though, that I see knock counts almost exclusively within the first few minutes of driving. Because I'm doing nearly back-to-back runs, my initial coolant temp is almost always above 200° (thermostat is 180°) and I'm in closed loop. With the car already hot and out of open loop, any idea why it would knock more in the beginning? Do the pistons cool down enough in 15min for piston slap to cause false knock?
On another note, is there any reason for me to touch the PE spark advance and closed TPS spark advance tables? I hear people leave PE as it is at 0° for smoother power? And none of my sources mentioned tuning the closed TPS table.
A few things could be going on, it could be knocking because the water temperature is above 200 degrees when you start data logging on a warm start and after a few minutes of driving the water temp drops low enough to eliminate the the knock. You also could be having some piston slap at start-up and you need some time for the pistons to heat up and expand again to eliminate the false knock.
Are you using premium fuel? How close is your low RPM and load timing table to stock?
Leaving PE at 0 degrees seems like a poor way to make the engine smooth, unless they are adding all the timing into the main timing table to achieve the correct WOT timing. The reason there is a main table and a PE table is to allow better fuel economy if the car is operating in closed loop and high load values. The reduced timing keeps the car from pinging at high throttle loads like the factory programs in. In my opinion you should lower the throttle loads for PE activation so the car enters PE earlier. If you are at 70% throttle you should be in PE and not closed loop like the factory programs. I tune all of my timing into the main timing table and do not use the PE table but that is because I activate PE earlier and don't need to worry about lean high load conditions, hot conditions.
A few things could be going on, it could be knocking because the water temperature is above 200 degrees when you start data logging on a warm start and after a few minutes of driving the water temp drops low enough to eliminate the the knock. You also could be having some piston slap at start-up and you need some time for the pistons to heat up and expand again to eliminate the false knock.
Are you using premium fuel? How close is your low RPM and load timing table to stock?
Leaving PE at 0 degrees seems like a poor way to make the engine smooth, unless they are adding all the timing into the main timing table to achieve the correct WOT timing. The reason there is a main table and a PE table is to allow better fuel economy if the car is operating in closed loop and high load values. The reduced timing keeps the car from pinging at high throttle loads like the factory programs in. In my opinion you should lower the throttle loads for PE activation so the car enters PE earlier. If you are at 70% throttle you should be in PE and not closed loop like the factory programs. I tune all of my timing into the main timing table and do not use the PE table but that is because I activate PE earlier and don't need to worry about lean high load conditions, hot conditions.
Apologies for the lull here, it seemed to have gone away (I think, or maybe I just decided to live with it since I needed to get it smogged) and I must have just forgotten to reply. But now I'm back to tuning my engine, and the knocking is back too.
I keep dropping timing 3-4 degrees at a time, and it doesn't seem to be improving things. On my last datalog, I was getting knocks in a cell (1000 RPM/30kPa) running just 15 degrees of timing! I don't have the experience a lot of you guys do, but to me it seems that knock counts at such little timing indicates false knock?
In answer to your questions, I am using 91 octane, and my current timing table in the relevant cells is almost exactly the stock table minus 10 degrees.
The knocking persists throughout a 30min drive, so I don't think initial coolant temps or piston slap are the issue.
So what are your PE settings? 70% TPS min, 90 kPa min, +0 degrees timing across the board, and about a 20% change to AFR?
Last edited by C4ProjectCar; 08-02-2017 at 12:47 AM.
The low-RPM knock seems to go away after about 5 minutes of warm-up, which seems to me to point to piston slap.
Should I be concerned that it seems to be a lot worse than it used to be? If I remember correctly, a couple months ago it would go to 20 knock counts, but on my last datalog it hit 90 (all before the 5-minute mark, then only a couple in the remaining 15 minutes of the log).
EDIT:
My last run was similar. However, I started out with a hot engine--coolant temp 184 °F and oil temp 152 °F--which I would think would eliminate piston slap from the get-go. 88 knock counts by the 5-minute mark, rising to 92 in the remaining 15 minutes. A few more things I've noticed: it will get a few knock counts in those initial 5 minutes if I lightly rev it (the knock counts appear as the engine is coming back down), the knocks seem to rise in large bursts, as shown below, and--this may be my imagination--it seems to knock more readily in first or second gear.
I'd really appreciate anything you guys could do to assist me in diagnosing this. I'm getting a little worried upon looking at logs from a few months ago and seeing just 5-10 knock counts in a comparable drive.
Is it possible my plugs are too hot? They're the stock L98 plugs, I believe.
Maybe the transmission? Valvetrain noise?
Aggregate knock map from last 5 datalogs
Last edited by C4ProjectCar; 08-03-2017 at 09:10 PM.
I think I'm getting somewhere with the knock counts! I was driving with my windows down, holding the car at 1250 RPM, and I noticed a squeaking sound. So I came home, popped the hood, and tried to reproduce it. Sure enough, right at 1250 RPM something is squeaking. I tried to get a video of it, but it seems to be intermittent: I got one squeak on my video, and then it stopped.
06-05-2017, 02:19 AM
Knock Counts at 1250 RPM
