Spark timing - Low Octane, how does the car know?

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JohnDee68
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cars: L36 Vx Series 2 8/2002 Acclaim Wagon 3.8L ECOTEC II.
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Spark timing - Low Octane, how does the car know?

Post by JohnDee68 »

Hi,
In TunerPro there is a Spark table for "Low Octane".
How does a car know if is low octane fuel compared to standard and what octane would it be considered as low and what normal?
Charlescrown
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Re: Spark timing - Low Octane, how does the car know?

Post by Charlescrown »

From other cars that I have when the ECU detects ping it swaps to another map with less timing advance and of alls well it switches back and if it pings it then swaps back to the low map. I believe Subaru will run on the low octane map for some time before switching back.
JohnDee68
Posts: 249
Joined: Fri Feb 02, 2018 7:05 pm
cars: L36 Vx Series 2 8/2002 Acclaim Wagon 3.8L ECOTEC II.
Location: South Australia

Re: Spark timing - Low Octane, how does the car know?

Post by JohnDee68 »

Thanks Charlescrown,
I thought there would be some way the car could possibly work it out. Just wasn't thinking it was ping related. But that would make sense I guess.
In-Tech
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Re: Spark timing - Low Octane, how does the car know?

Post by In-Tech »

This is what I was told by a GM engineer. During crank, it will throw an incredible amount of timing on one cycle, then it "listens" how many decibals the "ring" is and decides a blend from the tables from there. I'm sure most of us have heard the knock during crank.
JohnDee68
Posts: 249
Joined: Fri Feb 02, 2018 7:05 pm
cars: L36 Vx Series 2 8/2002 Acclaim Wagon 3.8L ECOTEC II.
Location: South Australia

Re: Spark timing - Low Octane, how does the car know?

Post by JohnDee68 »

In-Tech wrote:This is what I was told by a GM engineer. During crank, it will throw an incredible amount of timing on one cycle, then it "listens" how many decibals the "ring" is and decides a blend from the tables from there. I'm sure most of us have heard the knock during crank.
I can't see how the loudness of a knock can determine the octane of a fuel being burnt.
As knock loudness will vary depending on too many variables within the mechanics of the motor.
In-Tech
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Re: Spark timing - Low Octane, how does the car know?

Post by In-Tech »

Hi John,
Keep in mind he might have been speaking to me in lay terms and I really don't care :mrgreen: If you find a better knock strategy than what GM does, I would be glad to listen. The guy I was speaking with may not have a full understanding either. :thumbup:
immortality
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cars: VH, VN, VS, VX

Re: Spark timing - Low Octane, how does the car know?

Post by immortality »

My understanding is that it runs in the high octane table if the engine detects knock over a certain threshold then it drops to the low octane table. IF you run a datalog and go to the Data monitors tab you can show knock counts/knock retard on the displays where you can see how much timing the knock sensor are pulling.

If I'm not mistaken this feature (high/low octane tables) was not used by Holden in the factory tunes even though clearly the capacity was there. The1 set it up in his Enhanced tunes to work as intended. The1 modified a lot of this in his code. He is probably the best person to explain it.
In-Tech
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Re: Spark timing - Low Octane, how does the car know?

Post by In-Tech »

I would love to learn more about it. The aftermarket is sorely behind. AEM and Pectel seem to have plenty of ways to "tune" it if desired. It seems to never be discussed and is a "black art" of sorts.
JohnDee68
Posts: 249
Joined: Fri Feb 02, 2018 7:05 pm
cars: L36 Vx Series 2 8/2002 Acclaim Wagon 3.8L ECOTEC II.
Location: South Australia

Re: Spark timing - Low Octane, how does the car know?

Post by JohnDee68 »

It would be good to know what and how it actually would work. Presuming it then is related or adjusted by determining the knocking of the motor. I am curious as to know more about it. Maybe The1 might be able to shed a little light on to it more? No pressure.

Thanks guys, every day is a good day when we are able to still learn new things.
immortality
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cars: VH, VN, VS, VX

Re: Spark timing - Low Octane, how does the car know?

Post by immortality »

Have you read the help pdf for the enhanced tunes? Fairly sure it covers some of the changes he's made including the knock sensors.

I'd suggest doing a bit of searching about knock and knock ears on this forum. I do believe there was a bit of in depth discussion on this topic in one of those threads.
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