Quote: Originally posted by LarryBible Because of the knock sensors in all MB gas engines since the mid eighties, regular will not DAMAGE the engine, but it is false economy. Once the knock sensor detects knock the system will automatically retard ignition timing reducing power and efficiency. Put Premium in it. Good luck, A QUESTION? when you fill up again after you have run regular with premium .. how does the computer detect this and advance the system??

Looks like Joe was right.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Pretty simple. The computer advances ignition timing until it " hears " knock.
Then it retards the timing in small increments until knock is gone.
I.e., you cheap out on octane rating, you will end up with less timing advance & slightly less torque/hp/snap, balls, whatever you want to call it.
The difference would be hard to notice for some people.

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2007 C 230 Sport.

M103s don't have knock sensors, and will rattle, ditto for M117/M119 early with K-jet.

Play it safe, use premium. Detonation at high speed, when you cannot hear it, will roast the piston crowns and valves, not cheap.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Right on psfred! I once purchased an off-lease vehicle that required premium unleaded, and shortly after owning it the check engine light came on. The car ran fine, but I brought it to the dealer to have it checked out and they discovered that one valve was dead and the others looked pretty lousy. The tech offered that the previous owner didn't use premium. Thankfully the work was covered under warranty, otherwise it would have been a $2,000 lesson on why you should pay the extra pennies at the pump. Of course, the lessee didn't care.

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2004 E320 Wagon
1989 300SE
1998 Range Rover 4.0 SE

I know this is heading off-topic, but if the
M103 has no knock sensor, what effect is there to removing the
'retard resistor'?
Will it advance the timing beyond safe levels or just a little bit?
Thanks, Bob

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Bob Roe
Lehigh Valley PA USA
73 Olds 88, 72 MB 280SE, 78 Datsun 280Z, 71 T-Bird, 72 Olds 88, 83 Nissan Sentra, 85 Sentra, 73 230.6, 91 Integra, 83 300SD, 91 Volvo 940GLE wagon, 84 300SD, 95 Subaru Legacy L wagon, 02 Mountaineer, 91 300TE, 08 Murano, 2007 R320CDI 4Matic 52K, some Hyundai, 2008 BMW 535xi wagon all gone... currently
2007 Honda Odyssey Touring, 2011 Honda Odyssey Touring

The ignition timing/mixture program for the M103 is fairly complex, but I've heard that the resistor is there for certain modes, I think low speed low rpm high load or some such. removing it may cause knock (and may also get you some small amount of power at certain rpm).

I'd leave it alone, MB ain't gonna cheat you out of performance just to make the car slower (drive a C280 for proof).

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Yeah, I haven't been too tempted to unplug it. It's pretty well plastic-tied to a hose in an inacessible location, probably to preclude the casual tinkerer, like me.
Also I do notice a difference in throttle response with different fuel brands; my 300TE seems to be favoring Texaco premium, at least in this part of eastern Pennsylvania.
Now I need to remember to carry Techron and/or the Progard Fuel System Cleaner with me when I might be refueling.

One of the not so obvious benefits of using premium grade fuel is, that it contains a lot more detergent than cheapy gas.

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2007 C 230 Sport.

thanks manny.

HFM fuel injection systems, like that on the 1993 and later M104 engines, are designed so that idle speed can't be adjusted. Idle speed is completely controlled electronically. This HFM injection system also has adaptive technology that compensates for conditions such as engine wear and unmeasured intake air and is designed to maintain driveability as the engine ages.

HFM-SFI can retard engine knocking to just the knocking cylinders, unlike EZL technology, which retards spark timing across the entire engine. This keeps the ignition timing point as advanced as possible for maximum power output.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".