Gasoline
MBWorld Fanatic!
Joined: Jun 2010
Posts: 2,762
Likes: 630
From: Emmett, ID, USA
2007 GL450
It has been around 18 months on regular gas now, and my ECU's adaptations haven't even noticed. I almost wonder if something is wrong, but the engine runs fine and there is no audible knocking. This imperviousness may be due to my occasional use of high-strength PEA fuel additive (FYI Gumout Regane is best PEA/$ I found), cleaning carbon off the intake valves. Given the price difference between premium and regular, I could use a bottle every other tank and still come out ahead.
@Pmanc If you have a respectable scan tool, you can peek at your ECU adaptations.
One strategy would be to peek at the fuel adaptation every so often, and run Regane when it flips.
@Pmanc If you have a respectable scan tool, you can peek at your ECU adaptations.
One strategy would be to peek at the fuel adaptation every so often, and run Regane when it flips.
Out Of Control!!
Joined: Nov 2018
Posts: 11,463
Likes: 5,354
From: San Francisco Bay Area
2019 C63CS
For normal driving with the engine barely needing to make any power you'll be fine with lower octane fuel. Knocking/pre-ignition becomes an issue at high engine loads, like when you are towing or running the engine at WOT to redline. While the ECU will retard timing when knock is detected, the engine will still knock, because the ECU will continue to try to advance the timing again. Knocking over time will damage the engine. So the general advise is to take it easy and avoid high engine loads while running on octane that's lower than the recommended octane level. But for the daily grunt and stop&go traffic premium fuel makes no difference. The engine isn't working hard enough for knocking to become an issue. Just keep in mind that premium fuel tends to have higher grade and more detergents to clean fuel injectors and such.
MBWorld Fanatic!
Joined: Jun 2010
Posts: 2,762
Likes: 630
From: Emmett, ID, USA
2007 GL450
For normal driving with the engine barely needing to make any power you'll be fine with lower octane fuel. Knocking/pre-ignition becomes an issue at high engine loads, like when you are towing or running the engine at WOT to redline. While the ECU will retard timing when knock is detected, the engine will still knock, because the ECU will continue to try to advance the timing again. Knocking over time will damage the engine. So the general advise is to take it easy and avoid high engine loads while running on octane that's lower than the recommended octane level. But for the daily grunt and stop&go traffic premium fuel makes no difference. The engine isn't working hard enough for knocking to become an issue. Just keep in mind that premium fuel tends to have higher grade and more detergents to clean fuel injectors and such.
Reiterating the points from my post above:
The ME9.7 ECU adapts ignition timing to "low quality fuel". It appears to have two maps, although it could learn a large number. The ECU Variant Coding for this is "Low Quality Fuel" No/Yes.
The key engine cleaning ingredients can be found on the auto parts store shelf. The most important ingredient, polyethyl amine, or PEA, is found at the best price point in Gumout Regane Complete. About $8bux a bottle at Auto Zone.
Possibly the most "intelligent" approach to the gas quality choice would be to monitor the ECU adaptation, and when it switches to "Yes", run a tank of Regane gas and then reset the switch back to No.
Or put an endoscope in to see how carboned the intake valves are. In one period, I had such bad carbon that it disabled the engine; I repaired it by rigging water injection for the worst cylinders. The problem has not recurred, but I have also avoided doing repeated short trips in the winter, and have been periodically running tanks with Regane. If I had more initiative, I'd pull the plugs and take a look at the valves - but the fuel timing adaptation has not reset to Yes.
Senior Member
Joined: Aug 2018
Posts: 412
Likes: 122
From: Kelowna, BC
08 GL320 CDI
But these are direct injection engine, this trick wont really work as nothing is getting sprayed onto the intake valves.
Trending Topics
MB World Stories
The Best of Mercedes & AMG
6 Mercedes Models That Did NOT Age Well (But Are Somehow Still Cool)
Verdad Gallardo
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping
Verdad Gallardo
MBWorld Fanatic!
Joined: Jan 2016
Posts: 2,749
Likes: 881
From: In the Shadow of the Tetons
2013 ML350 Bluetec
Would I be wrong to mention that knocking (pre-ignition, AKA dieseling) is not as much of an issue at higher altitudes? At sea level it is more prevalent due to cylinder pressures being higher just because of atmospheric pressure.
Obviously if you've got a turbocharged engine the above doesn't apply.
Obviously if you've got a turbocharged engine the above doesn't apply.
Out Of Control!!
Joined: Nov 2018
Posts: 11,463
Likes: 5,354
From: San Francisco Bay Area
2019 C63CS
Would I be wrong to mention that knocking (pre-ignition, AKA dieseling) is not as much of an issue at higher altitudes? At sea level it is more prevalent due to cylinder pressures being higher just because of atmospheric pressure.
Obviously if you've got a turbocharged engine the above doesn't apply.
Obviously if you've got a turbocharged engine the above doesn't apply.
MBWorld Fanatic!
Joined: Jun 2010
Posts: 2,762
Likes: 630
From: Emmett, ID, USA
2007 GL450
People also get confused by direct gasoline injection's tendency to accumulate carbon from crankcase vapors on the manifold side of the intake valves.
My valve carbon was on the bottom, combustion chamber side, likely due in part to oil leakage past the valve stem seals. But all the intake valves had some carbon on them, and the owner's manual even points out that such carbon buildup is a known problem. Something about the valve stem seals on this motor? Or how the fuel droplets swirl in the combustion chamber before ignition?
