Engine Knock
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Joined: Mar 2006
Posts: 66
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From: WA, USA
I've got it too. It's really weird, and I do not like it at all. I can drop the revs to 2K rpm or lower on a flat road with no knocking, but I always get knocking almost exactly at 2500 rpm coming up the rpm range under light throttle. It's very reproducible. I always use Chevron or 76 92 octane here in WA.
Dealer technician says I am "lugging" the engine.
The motor in my 1974 Datsun B210 knocked less.
Dealer technician says I am "lugging" the engine.
The motor in my 1974 Datsun B210 knocked less.
Thread Starter
Poseur
Rennlist Member
Rennlist Member
Joined: Nov 2005
Posts: 17,745
Likes: 301
From: Santa Barbara, CA
After adding the ST104 octane additive it went away for that tank. Now it is back. Clearly, it is exactly what it appears to be,--insufficient octane and knocking. Can PCNA make a new EPROM with different mixture values for the California market? Should they?
Banned
Joined: Jan 2004
Posts: 3,473
Likes: 2
From: Pacific Northwest
Here's a somewhat related thread in the 996 forum that I posted:
https://rennlist.com/forums/996-forum/358537-engine-knocking-w-giac-chip.html
I bought the car in CA and moved it up to WA
https://rennlist.com/forums/996-forum/358537-engine-knocking-w-giac-chip.html
I bought the car in CA and moved it up to WA
Advanced
Joined: Mar 2006
Posts: 66
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From: WA, USA
Originally Posted by Benjamin Choi
Here's a somewhat related thread in the 996 forum that I posted:
https://rennlist.com/forums/showthread.php?t=358537
I bought the car in CA and moved it up to WA
https://rennlist.com/forums/showthread.php?t=358537
I bought the car in CA and moved it up to WA
It really doesn't seem right that the knocking mostly occurs under very light throttle.
Banned
Joined: Jan 2004
Posts: 3,473
Likes: 2
From: Pacific Northwest
I hit up the GIAC guys and their response is that the car is tuned for 98RON fuel from Porsche, but in the state of WA like CA, regardless of octane, we are filling up with 95RON fuel which might be the culprit causing the engine knock. Not sure if it's true that in WA and CA we're running 95RON. This is the first time I'm hearing about RON.
It always seems to happen around 3K, but not sure precisely at which RPM and it doesn't happen all the time, but might happen more often if I'm going up a hill or some grade.
It always seems to happen around 3K, but not sure precisely at which RPM and it doesn't happen all the time, but might happen more often if I'm going up a hill or some grade.
Burning Brakes
Joined: Feb 2006
Posts: 1,128
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From: Chicago area, IL USA
(Research Octane + Motor Octane) / 2 == AKI or Anti Knock Index
Research octane is determined in a very specific test engine with a fixed ignition advance. Motor octane is more realistic in auto engine applications, and uses a different test regime that better replicates real world engine parameters...
For a given fuel, RON is higher than MON, so we add the 2 and divide by 2 to get AKI - the anti knock index. AKI is what is displayed on the pump in the US - 89, 91, 93, whatever.
87 octane in the US is equivalent to 91-92 RON in Europe. In Europe, RONs of 95 == US AKI #s of 90-91. In Europe, midgrade is 98 RON, and premium would be 100 RON (or so).
Sorry, this doen't help the discussion much but I saw Benjamin's response and... :-)
-don
Research octane is determined in a very specific test engine with a fixed ignition advance. Motor octane is more realistic in auto engine applications, and uses a different test regime that better replicates real world engine parameters...
For a given fuel, RON is higher than MON, so we add the 2 and divide by 2 to get AKI - the anti knock index. AKI is what is displayed on the pump in the US - 89, 91, 93, whatever.
87 octane in the US is equivalent to 91-92 RON in Europe. In Europe, RONs of 95 == US AKI #s of 90-91. In Europe, midgrade is 98 RON, and premium would be 100 RON (or so).
Sorry, this doen't help the discussion much but I saw Benjamin's response and... :-)
-don
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Racer
Joined: Jun 2006
Posts: 269
Likes: 1
From: Woodland Hills, CA
I live in CA and I have never had the knocking problem. I use Unocal 91. When I have time I drive about 7 miles to another Unocal station and mix in 4 gal. of 101 (could be 100, don't remember) to bring it up to 93.
Instructor
Joined: Apr 2007
Posts: 155
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From: Bayville, NJ
Knock should happen in very small amounts and very infrequently with an antiknock system. It should be almost gone within a month of using the same fuel in the same car with the same driver. You might want to have the knock sensor checked by having a dealer put a PST2 on it. As far as light throttle knock, it makes no sense to me. Knock is a function of cylinder pressure gone explosive. There should be low cylinder pressure at light throttle. I wonder if 2500 is where the low lift lobes quit and the high lift lobes kick in. Equally possible, could this be gear rattle from a slight pulsation that you misinterpret as knock? Gear rattle is much more common with light throttle, especially "feathering" the throttle.
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Joined: Mar 2006
Posts: 66
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From: WA, USA
Originally Posted by wdonovan
Knock should happen in very small amounts and very infrequently with an antiknock system. It should be almost gone within a month of using the same fuel in the same car with the same driver. You might want to have the knock sensor checked by having a dealer put a PST2 on it. As far as light throttle knock, it makes no sense to me. Knock is a function of cylinder pressure gone explosive. There should be low cylinder pressure at light throttle. I wonder if 2500 is where the low lift lobes quit and the high lift lobes kick in. Equally possible, could this be gear rattle from a slight pulsation that you misinterpret as knock? Gear rattle is much more common with light throttle, especially "feathering" the throttle.
It's not like the knocking occurs all the time, but it definitely happens once or twice everytime I drive around town. There hardly any knocking when I am on the throttle. But it is definitely easily reproducible for me when driving on a flat road in third gear around 2500 rpm and giving it very slight throttle (just enough to raise the rpms to about 2750).
The dealer did check the knock sensor with the PST2, and said that everything was "within spec."
Can you say more about gear rattle? What gears are rattling?
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Joined: Sep 2004
Posts: 55
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From: Montreal, Canada
In the Montreal area the standard ocatane of 'super' is 91. Using this fuel I get the same knocking as you describe along with jerking and hesitation occasionally. There is one oil company that sells 'extra super' that is 94 octane. The car never knocks or complians. This is my standard fill now, even though it costs the equivalent of .50 a gallon more than the regular 'super'.
Frequently I travel to the east coast of the US (Vermont, NY, NH, Mass). The 93 octane available in this region runs fine as well. But every time I go back to the 91 octane for a couple of tanks the car performs lousy around town when accelerating. My suggestion, try some octane boosters.
Frequently I travel to the east coast of the US (Vermont, NY, NH, Mass). The 93 octane available in this region runs fine as well. But every time I go back to the 91 octane for a couple of tanks the car performs lousy around town when accelerating. My suggestion, try some octane boosters.