GL Class (X164) 2007-2012: GL320CDI, GL420CDI, GL450, GL550

Adaptation to regular gas

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Old Apr 17, 2023 | 11:32 PM
  #26  
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Mercedes Benz 2007 GL450 , 2012 BMW 528i
I have been running sam's club 87 for last 3 years. Approximately 25K local miles. I don't have the tool to check fuel quality flag in system, but no performance issues. I run a bottle of gum out twice a year.
At max highway mileage has been about 19-20/gallon. Everyday mileage computed by ECU is about 12.5mpg.
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Old Apr 18, 2023 | 09:25 AM
  #27  
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From: Emmett, ID, USA
2007 GL450
Originally Posted by Max Blast
Yeah, maybe I can hook up the tool and see what mine still set at at… I’ve been driving regular for well over a year, about 12 K and I have never heard a ping out of the motor. Just a re-cage everybody’s brains, the day I switched to 87 octane on an almost empty tank; from the drive home from the station the ECU had sensed and automatically set the low octane flag so I didn’t have to do anything in star to make this happen.
So I would be very shocked, appalled and surprised if that flag were now set to no.
And no way in heck am I going to set it to yes with 87 in the system.

I am still a little fuzzy on how the actual adaptation occurs, whether it’s a set number of pings over a certain amount of time that automatically retards everything and sets the low octane flag. And then, conversely, in order for the ECU to set the low octane flag to no?
Speculating: The system does not have a way to set the flag to "No". After all, that would be inspired by the absence of symptom: no knocking. The system could continually test by advancing the spark, but that would mean it would be continually risking knocking. Which wouldn't be the end of the world; diesel engines "knock" on every compression stroke - but I'm pretty sure the engineers would not approve.

IF you were interested in doing the experiment, I would put a tank of premium in, along with cleaner, and set the flag back to No. Then resume the regular after that tank is dry.

I am curious to peek inside my own motor's cylinders again to check whether the carbon deposits are still present.
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