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Variable Ignition Timing Based on Knock Sensors #4473480
07/28/17 10:20 PM
07/28/17 10:20 PM
Joined: Jul 2012
Posts: 2,103
Nashville, TN via Memphis
john_pifer Offline OP
john_pifer  Offline OP
Joined: Jul 2012
Posts: 2,103
Nashville, TN via Memphis
So, my question is really, how long is the cycle.

Let's say it's late July in Tennessee, almost 100 outside. I'm driving my Tacoma down a highway at 55 mph in high gear. The road grade starts to go uphill and I tip into the throttle a little bit, just to maintain my speed, but not enough for the automatic to downshift. I hear some light pinging, which is pretty normal. I've spiked cylinder pressures by cracking the throttle open even more at a not-very-high RPM.

SO, let's say I had been burning 93-octane fuel, but, on my last stop, I filled up with 87-octane pee water. Presumably, the knock sensors would detect any knock (how sensitive they are, I'd also like to know - will the sensors pick up pinging, or, would it have to be an actual knock event?) and pull the timing back a little bit.

OK, let's say, 300 miles down the road, I fill up with 93 again. How long does it take my ECU to re-advance my ignition timing and give me back my few extra HP & LB/FT? If I floor it and redline my engine through the first 3 gears as I'm merging back onto the highway, does the ECU then detect the fact that there was no knock, and advance timing again? Or, is there a timeframe that it has to get through with no knock, in order for the timing to be re-advanced?


16 WRX - PPPP
07 Tacoma V6 - M1 EP 5W-30, Fram Ultra, 10K OCIs, 198K
07 Yamaha R1 - Rotella T6 5W-40, Bosch 3300
07 Yamaha YZ-250, Klotz, Rotella

Re: Variable Ignition Timing Based on Knock Sensors [Re: john_pifer] #4473567
07/29/17 12:40 AM
07/29/17 12:40 AM
Joined: Sep 2009
Posts: 25
SA
LvR Offline
LvR  Offline
Joined: Sep 2009
Posts: 25
SA
There is a whole set of "War and Peace" like novels to be written on the subject ................... so imo its too manufacturer specific, model specific, and engineering approach specific to make a "generalized" statement.


Last edited by LvR; 07/29/17 12:42 AM.
Re: Variable Ignition Timing Based on Knock Sensors [Re: john_pifer] #4473623
07/29/17 05:13 AM
07/29/17 05:13 AM
Joined: Nov 2004
Posts: 7,752
Texas
GMBoy Offline
GMBoy  Offline
Joined: Nov 2004
Posts: 7,752
Texas
In the case of GM vehicles the PCM's fuel trim and timing "maps" are always the same. This means the vehicle will always attempt max timing advance/fuel trim every time - the knock sensors pull timing back but next full throttle or other load event will have the car again attempting full advance.....the knock sensors control how much advance is allowed. This is the short version of a long and complicated strategy. Hopefully this will explain it a little.

Re: Variable Ignition Timing Based on Knock Sensors [Re: LvR] #4473627
07/29/17 05:38 AM
07/29/17 05:38 AM
Joined: Oct 2008
Posts: 19,084
Sunny Florida
SteveSRT8 Offline
SteveSRT8  Offline
Joined: Oct 2008
Posts: 19,084
Sunny Florida
Originally Posted By: LvR
There is a whole set of "War and Peace" like novels to be written on the subject ................... so imo its too manufacturer specific, model specific, and engineering approach specific to make a "generalized" statement.


Exactly, wildly platform specific.

Our sig car's knock sensors are so sensitive that you never hear knock even when premium is not used. Our newer fleet trucks are GM and I've never heard any audible knocking there either.


"In a democracy, dissent is an act of faith."
J. William Fulbright
Best ET-12.79 @ 111 mph
4340 pounds, Street tires
Just like we go to Publix
Re: Variable Ignition Timing Based on Knock Sensors [Re: john_pifer] #4473708
07/29/17 08:23 AM
07/29/17 08:23 AM
Joined: Dec 2015
Posts: 154
Memphis TN
Excel Offline
Excel  Offline
Joined: Dec 2015
Posts: 154
Memphis TN
I have noticed in TN that our 87 pings way more than in other states
I would say what gas we buy is not the same state to state .

After multiple road trips from TN to Florida and other places I ping the most
in my home state,no matter what brand . I think we are not getting what we expect
at the pumps


2015 Ford F150
2015 Ford Mustang GT,Whipple powered
2017 Yamaha FZ09

Re: Variable Ignition Timing Based on Knock Sensors [Re: john_pifer] #4473721
07/29/17 08:38 AM
07/29/17 08:38 AM
Joined: Aug 2011
Posts: 9,560
Boston, MA
HerrStig Offline
HerrStig  Offline
Joined: Aug 2011
Posts: 9,560
Boston, MA
What octane does the manual stipulate?

Re: Variable Ignition Timing Based on Knock Sensors [Re: john_pifer] #4473755
07/29/17 09:35 AM
07/29/17 09:35 AM
Joined: May 2013
Posts: 2,093
Saskatchewan, Canada
Johnny2Bad Offline
Johnny2Bad  Offline
Joined: May 2013
Posts: 2,093
Saskatchewan, Canada
Knock sensors are notorious for being ineffective, I wouldn't rely on one to keep detonation at bay. Think about the job they are asked to do ... decide which engine noise is knock, and which is some other normal engine noise/vibration. Nearly impossible. I would keep a can of Octane Boost in the truck instead, using it when you are stuck with a grade lower than you need. Much safer procedure.


'57 FL Straight 50 wt
'90 Miata 1.8L w/Rotrex Supercharger [Mobil1 0W-40]
'96 Ram 1500 [3.7L Mobil1 0W-20 / 1L 15W-50]
'01 PT Cruiser [Mobil1 0W-40]
Re: Variable Ignition Timing Based on Knock Sensors [Re: Johnny2Bad] #4473759
07/29/17 09:45 AM
07/29/17 09:45 AM
Joined: Jul 2012
Posts: 663
Perth, Western Australia
Brad_C Offline
Brad_C  Offline
Joined: Jul 2012
Posts: 663
Perth, Western Australia
Originally Posted By: Johnny2Bad
Knock sensors are notorious for being ineffective, I wouldn't rely on one to keep detonation at bay. Think about the job they are asked to do ... decide which engine noise is knock, and which is some other normal engine noise/vibration. Nearly impossible. I would keep a can of Octane Boost in the truck instead, using it when you are stuck with a grade lower than you need. Much safer procedure.


Que? What tripe. Knock sensors have been installed for decades because they work. Do you really thing manufacturers would take the time to design and tune them on a system if they were ineffective?

If you actually understood how they worked, and how the algorithms in the ECUs very effectively mask out the mechanical noise you refer to, you might have a better understanding of just how effective they really are. Once you've put a scope/logger on a vehicle and seen the ignition retard individually on single cylinders to cope with anomalies you'd be blown away at how "effective" they are.

Don't let the facts get in the way of a good conspiracy theory though. Much better to add some "miracle in a can" to the tank. Oddly enough, if your miracle in a can is any good (and again you were actually watching the ignition) you'd see the ECU slowly advance the ignition to actually take advantage of the extra octane your elixir bestows upon your chariot.

Re: Variable Ignition Timing Based on Knock Sensors [Re: john_pifer] #4473764
07/29/17 09:48 AM
07/29/17 09:48 AM
Joined: Oct 2012
Posts: 4,602
Taiwan
Ducked Offline
Ducked  Offline
Joined: Oct 2012
Posts: 4,602
Taiwan
Originally Posted By: john_pifer
Presumably, the knock sensors would detect any knock (how sensitive they are, I'd also like to know - will the sensors pick up pinging, or, would it have to be an actual knock event?)...


Doubt that's an "officially" defined distinction, which it would need to be before the question could be answered by anyone.

Re: Variable Ignition Timing Based on Knock Sensors [Re: Johnny2Bad] #4473773
07/29/17 10:01 AM
07/29/17 10:01 AM
Joined: Sep 2009
Posts: 25
SA
LvR Offline
LvR  Offline
Joined: Sep 2009
Posts: 25
SA
Originally Posted By: Johnny2Bad
Knock sensors are notorious for being ineffective, I wouldn't rely on one to keep detonation at bay. Think about the job they are asked to do ... decide which engine noise is knock, and which is some other normal engine noise/vibration. Nearly impossible.............................


Well - read my first post again and then realize this is in fact the only instrument/sensor found on most current engines that allow the ECU to actually cope with the garbage fuel found in some places ............................... without it EVERYBODY would ALWAYS have to drive on a pre determined fixed (read expensive) RON/MON fuel in order to allow ALL ECUS to manage combustion effectively.

Re: Variable Ignition Timing Based on Knock Sensors [Re: john_pifer] #4474107
07/29/17 07:43 PM
07/29/17 07:43 PM
Joined: Jul 2003
Posts: 4,746
New Zealand
Silk Offline
Silk  Offline
Joined: Jul 2003
Posts: 4,746
New Zealand
The Mitsubishi MUT III factory scanner shows knock learn - how much it is retarding from the 100% standard setting. Something we always look at with a GDI, normal engine shows nothing, as they are made to run on our fuel. My Volvo should run on a premium fuel, but I run it on the low octane, on a trip I put in premium, and fuel economy comes up a few kms later. I guess it remaps, but haven't bothered to watch ign advance on the scanner...a bit dangerous.


1987 BMW R65 - Penrite V Twin 20/50
2005 Nissan Expert - Gulf Western 10W-40
1996 Volvo T5 - Penrite HPR15 - 15W-60. Ryco syntec filter.
Re: Variable Ignition Timing Based on Knock Sensors [Re: john_pifer] #4474169
07/29/17 09:21 PM
07/29/17 09:21 PM
Joined: Jul 2017
Posts: 43
Tennessee
OilSwag Offline
OilSwag  Offline
Joined: Jul 2017
Posts: 43
Tennessee
I agree with the above about each manufacturer being different. It all depends on ecu programming along with the sensitivity of the knock sensor. Sme more so than others. The ultimate goal is the ecu adjusts before there is knock. I went from a Ford modular 2valve to a Infiniti VQ engine. I swear I can't make that car knock. Even with 87 octane at low rpm high load. So the ecu is pulling time before there is a chance at a audible knock. You can get knock and not notice it in sound. So in Infiniti's scenario the car has timing being pulled before there is an audible knock. In my opinion the knock sensor is doing it's job and the ecu was programmed well. My Mustang would knock like [censored] with less than 93 and not adjust to it. I think it's best to not let knock happen. Use an octane booster that works if you need to


03 Infiniti G35 209K, Castrol Edge 5W30 topped with Edge HM, Fram Ultra Filter, Berryman/MMO fuel maintenance in 93 E0, all synthetic fluids
Re: Variable Ignition Timing Based on Knock Sensors [Re: john_pifer] #4474173
07/29/17 09:26 PM
07/29/17 09:26 PM
Joined: Jun 2003
Posts: 33,073
ME
eljefino Offline
eljefino  Offline
Joined: Jun 2003
Posts: 33,073
ME
Saturn S-series was quick to pull and slow to give back.

Mine would drink a slug of oil after coasting down hill in gear, knock, and get a "flat spot" in acceleration that took ~200 miles to work out.

That car took very well to water decarbonization.

Re: Variable Ignition Timing Based on Knock Sensors [Re: eljefino] #4474287
07/30/17 12:46 AM
07/30/17 12:46 AM
Joined: Jul 2012
Posts: 2,103
Nashville, TN via Memphis
john_pifer Offline OP
john_pifer  Offline OP
Joined: Jul 2012
Posts: 2,103
Nashville, TN via Memphis
Originally Posted By: eljefino
Saturn S-series was quick to pull and slow to give back.

Mine would drink a slug of oil after coasting down hill in gear, knock, and get a "flat spot" in acceleration that took ~200 miles to work out.

That car took very well to water decarbonization.


Ha! That's interesting!

My WRX, being a 2016, and TGDI, and, being prone to LSPI, you would think it would have the most sophisticated anti-knock programming, that would keep it from knocking at all, right? Wrong. Must be a hard engine to keep from knocking, because it will knock from time to time. And I'm not talking the light pinging I get from the Taco on [censored] 87 fuel going uphill in hi gear in 100 heat. The WRX will knock hard enough that it actually momentarily loses power. This is if I'm in high gear at, say, 65 mph and I open the throttle to, say, 50-60% to pass someone. Classic LSPI. And I only use Top-Tier 93 in that car. Usually Shell. Must be hard to account for. But...then again...they didn't do a great job of EFI tuning in that car anyway.


16 WRX - PPPP
07 Tacoma V6 - M1 EP 5W-30, Fram Ultra, 10K OCIs, 198K
07 Yamaha R1 - Rotella T6 5W-40, Bosch 3300
07 Yamaha YZ-250, Klotz, Rotella

Re: Variable Ignition Timing Based on Knock Sensors [Re: john_pifer] #4474328
07/30/17 03:44 AM
07/30/17 03:44 AM
Joined: Mar 2015
Posts: 5,022
Virginia
bbhero Offline
bbhero  Offline
Joined: Mar 2015
Posts: 5,022
Virginia
Isn't 87 octane more volatile than 93?? Would the ECU actually advance timing for lower grade 87 due to it being more volatile?? And pull back timing for 93 being that it is less volatile?? Therefore the ECU would take more advantage of the 93 by pulling back timing and actually compensate for 87 being advancing the timing.


Nissan Altima 3.5 Coupe
Quaker State High Mileage 5w30 Purolator Boss 14610
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