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Old 05-21-2012, 08:48 AM   #9
Scooby Specialist
Member#: 118500
Join Date: Jun 2006
Chapter/Region: MWSOC
Location: Michigan
02 Silver Wagon
"Stage 2"


Originally Posted by meebs View Post
I like checking in on my Fine Learning Knock Correction table every once in a while just out of curiosity (my wife attributes it to paranoia).

Normally I fill up with 76 as they are the only station left in my neighborhood that doesn't have the "May contain up to 10% Ethanol" stickers.

On my way out of town I filled up with Chevron, I don't recall ever having an issue with them. However, after our trip, I checked the table and hmm... there's one cell starting to show a correction. Normally my car is all zero's across the table and IAM is always at 1. I'm on a stock tune apart from lowering the values for the OL/CL delay, which the car has always been happy with.

So then after the tank of Chevron, I filled up with Shell on my way home...Maybe the marketing got to me.

My question then is does 20% more "Nitrogen" in their new formulation = 20% more knock? I think the numbers speak for themselves. Could this have just been a bad batch? I don't really want to ever try again to find out.

Here is my log of condensed Learning View readouts. Ever since I switched back to 76, my FLKC table has stayed at 0 in all cells.

04/18 Chevron
04/24 Chevron -1.05 @ 2.0-5.0 @ 4400-5600
04/26 Chevron -1.05 @ 2.0-5.0 @ 4400-5600
04/29 Chevron -1.05 @ 2.0-5.0 @ 4400-5600
04/30 Chevron -0.70 @ 2.0-5.0 @ 4400-5600
04/30 Chevron -0.70 @ 2.0-5.0 @ 4400-5600

Fill up with Shell

05/02 Shell -0.70 @ 2.0-5.0 @ 4400-5600
05/03 Shell -0.70 @ 2.0-5.0 @ 4400-5600
05/04 Shell -0.70 @ 2.0-5.0 @ 4400-5600

05/07 Shell
-1.05 @ 1.3-1.6 @ 3200-4400
-2.10 @ 2.0-5.0 @ 4400-5600

05/08 Shell
-1.05 @ 1.3-1.6 @ 3200-4400
-2.10 @ 2.0-5.0 @ 4400-5600

Mileage on car readout is 19.2.
Normal for me is 22.5

05/08 Shell - RESET ECU after 1/4 tank.
05/08 Shell 0 FLKC after 2 drives.
05/09 Shell 0 FLKC
05/10 Shell -1.40 @ 2.0-5.0 @ 4400-5600

05/10 76 Reset ECU add Gumout Fuel Injector cleaner and fill up on 1/8th of a tank with 76.

05/11 76 0 FLKC
05/17 76 0 FLKC 3/4 tank through.
05/19 76 0 FLKC

Does anyone else see this kind of fuel sensitivity between brands? Chevron, Shell and 76 are all considered "top-teir". While 76 does contain cleaning additives, my car appears happier with them. It seems to me like the less additives, the better. I'm almost considering trying Safeway or Arco (no additives) as a test, but I'm pretty sure they are all using 10% Ethanol as well, which could be unrelated though. Ethanol is supposedly what they use to control octane anyway.
I wouldn't worry so much. A lot of it comes down to the Ethanol content. Stoich for ethanol is 8.x:1, while E0, or gasoline is 14.7, so the more ethanol you have, the more fuel will have to be pumped into the engine to maintain stoich.

Knock correction is affected by so much, ambient air temp, fuel octane level, ambient humidity, and how many leaves or dead birds are on your TMIC. The corrections, short and long term are there for this very reason. I would have a hard time concluding that one fuel is better than the rest simply from the corrections in the ECU. There are SO many other variables that are changing, it's impossible to say it's all in the fuel.

If you hear knock, and the knock corrections are maxed out, then I would worry. You should get a CEL if this happens.
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