For all you w124 owners who havent already done this.... I upgraded my gas to super premium and now the car is driving like new...there is no low end hesitation...or engine rocking at idle...and acceleration and torque are much better.... It cost me almost 50$ to fill the tank...but the car sure was happy....

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***SAMI*****
1986 300E 240K
1999 Mitsubishi Spyder GS 60K

I have a 103 motor as do you. My owners manual calls for 91 octane. In my area super is 93, mid-grade is 89; the low end grade is 87. I've always used the 93 octane super.

Some posts here have claimed that you can use the 89 mid-grade octane.

If MB wanted 89 octane in the car, the owners manual would say 89; not 91.

My 2 cents.

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'91 300-SEL

If you are going to always run premium anyway, you should remove the ignition advance setting resistor near the master cylinder for maximum ignition advance.

On Euro cars there is a dial that is used to adjust ignition advance to accomodate the fuel octane. On US cars a fixed resistance is connected in its place. By removing this resistor and taping off the connector to prevent the entry of dirt, you are setting ignition to the max octane setting.

I did this some time ago and it does make a difference in power and will slightly increase fuel mileage AS LONG AS YOU BURN PREMIUM. Don't pull the resistor and then run low octane fuel, you will risk engine killing spark knock.

Have a great day,

Larry:

Is this on the M103 or does the M104 have the resistor too?

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Nooooo! The resistor trick does not work as advertised... I tried that on my 300E and promptly lost 10% in fuel economy over two tanks, it went back to normal when I re-installed the resistor. There was ZERO power gain. Pulling the resistor doesn't max out the advance, it puts the system into sort of a limp mode, but there's no real power loss either. Results seem to vary from car to car though, but I definitely don't recommend this particular mod. BTW - I was running premium at that time. With the resistor back in place I can run 89 octane with no adverse affects... no power loss, no knock, no loss in MPG. I don't recommend that either, as individual cars may react differently...

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Dave
Boise, ID
Check out my website photos, documents, and movies!

I had the same situation. When I posted my MPG loss, people thought I was lying. When I pulled that resistor, my car got worse gas mileage. I never even drove the car any harder, and I used 93 octane all the time. I put the resistor in and the MPG went back up. That R16 mod does not work on all M103's.

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1987 mercedes 300E
1995 e320 conversion(hated the 300e grill)
HID/Xenon (D2S)
Keyless Entry
Monochromatic Paint (Custom Blue)
Smoked Tails
Flat Badged (front)
Debadged (rear)
custom "carbon fiber" console
18 inch HP EVO rims
Sold! Now I drive a Monte Carlo SS
http://memimage.cardomain.net/member.../352975_67.jpg
http://memimage.cardomain.net/member.../748335_24.jpg

Seemed to work better for my CE than E. I can keep it pulled and still use mid-grade.

Some may be the placebo effect. I may put the resistor back and see what happens.

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1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus

1994 e320 Cabriolet 108k



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


[/SIGPIC]

Here in sunny So. Cal. I can only get 91 octane for my 86 300E, often blended with God know what these days. On hot days especially, I notice a fair amount of pinging, particularly when accelerating from a stop in 2nd gear going uphill. Sound like a can full of rocks under the hood. Is there a resistor value I can switch to that will allow me to retard the timing slightly overall? I'll put up with the loss of a little power or fuel mileage to prevent holing a piston.

Gary

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I am surprised that any improvement would be noticed running an M103 on higher octane fuel. Unlike the M104 which had a knock sensor and would benefit from higher octane fuel, the M103 did not. Possibly additives in the higher octane fuel cleaned the fuel system which resulted in the smoother running you mention in turn resulting in better performance. An M103 in good running order theoretically will not benefit from fuel of any higher octane from that which will allow it to run without knocking (pinging or pinking).

As Larry suggests, the ignition timing can be altered (advanced) by way of the R16 programming resistor which will result in slightly improved performance when used with higer octane fuel (mandatory). In some markets R16 was an adjustment accessible to the owner but in other markets (eg. USA and Australia) it was a single resistor in a plug in the wiring harness. Larry mentions as many have found that removing the R16 resistor plug programs the timing for greater ignition advance. Just be aware that this is not necessarily the case with all models fitted with the R16 resistor. I have found that for both my Australian delivery '90 190E and '90 300TE that removing R16 caused the ignition timing to default to a "limp mode" giving maximum retarded ignition timing. To achieve maximum timing advance I needed to fit a higher value resistor for R16 to each of my cars (a different value for each as well). This has previously been covered in these threads:
http://www.peachparts.com/shopforum/showthread.php?threadid=67772
http://www.peachparts.com/shopforum/showthread.php?threadid=67773

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

Greg, thanks for clearing that up!

Gary - if you are pinging with 91 octane, something is wrong! I'm not sure what but an M103 should be ping-free with 91 and probably 89 (at least mine is fine with 89 even when it's 100F+ outside and the engine is at 105C...) Yes you could put in a different resistor (higher does not mean more retard, btw) but you shouldn't need to change the resistor in the first place, assuming you have the original one installed.

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Dave
Boise, ID
Check out my website photos, documents, and movies!

Any ideas on what to check? It's been a problem since I've owned the car. I've tried every different brand of gas I can find, all with the same result; pinging under heavy load, mostly at low rpm but sometimes even at mid-range rpm (3000 - 4000). On one occasion I can recall, I had 3 passengers in the car on the freeway and accelerating up an incline from about 55 mph it started pinging.

I've pulled the plugs and inspected the combustion chambers as best I could but did not see any abnormal or excessive carbon buildup that might cause preignition. I've also checked the timing with a strobe and it seems to be within spec. I did have to replace the Engine Control Module at one point because it died, but the problem was there both before and after replacing the ECM.

As I recall, it calls for either 92 or 93 octane fuel, so 91 might be enough to make it ping, especially with the reformulated Calif. gas.

Is there a possiblilty that the fuel mixture may be too lean? Is there an accurate DIY way to check it?

Gary