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Author Topic: How does knock control work?  (Read 8983 times)
e_pacman
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« on: April 11, 2017, 10:18:19 AM »

Hi guys!
I have just bought a Porsche 997 Turbo to use as an extra daily driver when my Seat Leon 20VT needs a rest. The Porsche sometimes has a slight hesitation during full load acceleration. It happens around 3000-5000 RPM and not exactly the same every time. It's like a quick decline in acceleration, and a non-car guy might not even notice it. I have been trying to figure out what causes it, and the first step was to log timing with the Torque app and ELM327 adapter. Timing values look pretty similar to my Seat's, dropping to maybe 10-12 degrees mid range and increasing to 17-18 higher up.

The question is, what is the timing value from the standard PID telling me about the complete timing situation? I read somewhere that the PID shows cylinder 1 only, so could I have massive timing retard on other cylinders and not know it? Or will knock on a few cylinders cause all the others to retard as well, in which case I would see it on my log?

The ECU is a Bosch unit called DME-something. I figured someone on this forum might know something.  Smiley
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nyet
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« Reply #1 on: April 11, 2017, 10:46:13 AM »

There is no KR PID.
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e_pacman
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« Reply #2 on: April 11, 2017, 11:09:11 AM »

I know, but there is one for timing advance, right? Just trying to figure out if it is at all useful.
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nyet
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« Reply #3 on: April 11, 2017, 11:11:58 AM »

No, there is no ignition timing PID.

Recovery from KR is via basic hysteresis
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IamwhoIam
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« Reply #4 on: April 12, 2017, 12:57:39 AM »

He's talking about OBD PIDs https://en.wikipedia.org/wiki/OBD-II_PIDs not about PID controllers IMHO.
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I have no logs because I have a boost gauge (makes things easier)
e_pacman
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« Reply #5 on: April 12, 2017, 12:37:04 PM »

Oops, sorry about the confusion.   Wink Yes, I'm talking about the OBD PID (Parameter ID) for timing advance.

What I want to know is basically if what I'm seeing on the PID is just cylinder 1 (it says so at some places online), and if I would have crazy amounts of knock retard on another cylinder, would all others be retarded as well, so that I would see something on the PID signal?

It's not the smoothest signal in the world, but it's pretty consistant over several pulls so I think it should be somewhat representative for what's going on.
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vwaudiguy
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« Reply #6 on: April 12, 2017, 02:44:10 PM »

Plugs replaced recently? Correctly gapped?
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e_pacman
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« Reply #7 on: April 13, 2017, 05:06:52 AM »

Yep, plugs are only 1300 miles old. Replaced by certified Porsche Dealership so I would hope thay are correctly gapped. I didn't own the car at the time.
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IamwhoIam
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« Reply #8 on: April 13, 2017, 06:48:22 AM »

What gear was that log done in? Resolution looks piss-poor to me, but I'd say there isn't much wrong with 12.5 degrees timing at 4500 on a stock 997TT, so not sure what the "problem" is here.
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I have no logs because I have a boost gauge (makes things easier)
e_pacman
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« Reply #9 on: April 13, 2017, 10:01:17 AM »

3:rd gear. Right, good to hear from someone else that the timing looks pretty normal. The thing is I do feel a slight shutter in the car during hard acceleration that I'm pretty sure shouldn't be there, but I guess it's not from KR then. It sort of feels like the traction control is doing something, even though traction shouldn't be a problem at those speeds.
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nyet
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« Reply #10 on: April 13, 2017, 10:06:26 AM »

The thing is I do feel a slight shutter in the car during hard acceleration

Shudder usually means misfire
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nubcake
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« Reply #11 on: April 13, 2017, 10:09:17 AM »

Automatic?
Could be one of the torque limiters.
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Powerchips
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« Reply #12 on: April 14, 2017, 01:45:42 PM »

Check yours DVs
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e_pacman
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« Reply #13 on: April 15, 2017, 01:33:23 AM »

Automatic?
Could be one of the torque limiters.

Yes, automatic!

Sounds interesting, could you elaborate? Anywhere I can read about how that works?
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younes
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« Reply #14 on: April 15, 2017, 10:13:01 AM »

These models have poor ignition coils. Replace them.
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