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  #1  
Old 05-04-2001, 10:42 PM
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Location: Bridgetown, Nova Scotia
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I have a 300 Sel that I run Sunoco 94 octane gas in. Sometimes I can only get 91 or 92 octane when I am out of town where there are no Sunoco's. When I burn the lower octanes (91 or 92) My car works bad. Skips when I first start up for a second or two. I have tried putting in a bottle of octane boost but does not make a differance. As soon as I fill with 94 it works perfect. This is not making sense to me. There has to be another reason for this. Any ideas? I know everone that has a Mercedes does not run Sunoco gas. The car is a low miler 60k 1990, all new plugs wires cap and so forth. Could it be timing or wrong plugs? Any help would be great, I know someone out there has the answer. Thanks
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  #2  
Old 05-04-2001, 11:38 PM
Clauser1
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Youre not the only one.Last year on my way to Washington
D.C.I filled up my car w/ Sunoco 94 in Pennsylvania.
What a difference.I thought,my mind is just playing games w/ me because of the long drive and its 3:00 A.M.But my butt
is telling me something else.The engine run smoother and I
cant even hear a discordant note in my exhaust.
Its an exellent gas.Wish we have it here in Chicago.

Clauser1



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  #3  
Old 05-05-2001, 12:25 AM
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Join Date: Mar 2001
Posts: 326
I use 93 octane in most cases. There is no difference if I use 92 or 91 either. Runs like crap if I use 89 octane. The station I use buys whatever brand they can get cheap. They usually beat everyone else by as much as 10 cents/gal. With gas prices the way they are this is my main concern.We don't have Sunoco here either so I wouldn't have means to do a comparison. We do have Ammoco which is supposed to be very good.
Oh, I just remembered I do have access to 103 octane if the place still carries it.

Hey Clauser, what part of Chicago do live?
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  #4  
Old 05-05-2001, 05:10 AM
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Join Date: Jun 1999
Location: Surrey, Beautiful British Columbia, Canada
Posts: 750
here in the vancouver, canada, area chevron
and petro-canada are the only gas stations
that sells 94 octane reading.

i couldn't tell the difference in performance
when i use 91 to 94 octane gas. it's your choice,
and it's your money. cheers!!
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  #5  
Old 05-05-2001, 05:25 AM
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Join Date: Feb 2001
Location: Northumberland, UK
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I don't find a difference in smoothness, but I get much better fuel consumption on 97 Octane fuel as against 95 Octane. 97 is about 5 to 8 pence a litre dearer than 95 for me. They have 98 in continental Europe and it's pretty much the same price as 95 (unless I'm being dumb with the currency change, not unknown).

My manual warns me to go gently if using anything less than 95 and not to use less than 91.
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  #6  
Old 05-05-2001, 08:39 AM
Clauser1
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Scott,
I,live in the northside of Chicago.Western and
Peterson.Do you live in Chicago too?

Clauser1
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  #7  
Old 05-05-2001, 10:05 AM
Robert W. Roe's Avatar
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Location: Lehigh Valley PA
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C Holmes: Are you comparing oxygenated, and non-oxygenated fuels? Most pumps will tell you. I had a 91 Volvo 940GLE that wouldn't run happily on oxygenated Amoco premium. This was the only kind of gas available in Northern Virginia. As soon as I filled up a couple tanks in Pennsylvania, again with Amoco premium, the idle cleared up.

Perhaps you have carbon build-up in your engine? Maybe try to run a couple bottles of Techron through it and try an "Italian Tune-up"...
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  #8  
Old 05-05-2001, 01:13 PM
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regarding the cost difference in fuels the difference between cheap fuel and the best fuel is about $.25 a gallon. So at 15 gallons thats about $3.75 per fill up. If you fill up once a week thats $195.00 per year. That is not much money for good driving performance for a year and plus your repair bills in the long run for using cheap fuel could far far exceed your savings by using the cheap fuel..

I always use the best possible fuel I can find, its worth it. My 2 cents...
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  #9  
Old 05-05-2001, 10:33 PM
mattsuzie
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I am glad that someone brought up this topic. 95% of the time I burn 93 Amoco with great results, however, if I put in 87, 89 and other cheap gases in there is no notible difference perfomance difference other than I get a few miles less per gallon gas mileage.

I drive conservatively. Even though it saus on the fuel gause (Premium Gas Only), do I really have to fill up with 93 Octane. I once heard that was for only if you beat on the engine quite often. I don't know, will 87 and 89 damage the engine?

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  #10  
Old 05-05-2001, 11:22 PM
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Location: New Bedford, MA USA
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ACHTUNG Octane

This is always an interesting topic to discuss. in reality, the higher octane numbered fuels are not as combustible as the lower numbers. This is to prevent pinging knocking and engine damage associated with same. The lower numbers burn better, but can produce detonation. A lot of this is very scientific, but for me, I have used regular unleaded 89 RON for quite some time in my 300E, w/o any ill effects and excellent emission numbers. Also seems to run smoother. I think the effect will be different for each car, but I am happy and have saved a few pennys over the years.
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  #11  
Old 05-05-2001, 11:38 PM
Jason M.
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For those of you who dont run Hi-test

For those of you who dont run high-test, you could seriously damage your engine through long term preignition(also called detonation). This means that the fuel ignites completely before the cylinder has reached full compression. It can and does cause engine damage, deposits, and other harmful effects. Consider this, The MB owners manual says that 87 octane is only for extreme emergencies, and that when filled with 87 octane, the throttle must not be more than 2/3 open. MB does not have any residual income from mandating usage of High octane fuels, so you should probably trust them in this case.

Jason M.
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  #12  
Old 05-06-2001, 11:37 AM
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Well thanks for the input, but what I am saying is I cannot run anything less than 94 octane! I have found 92 or 93 runs the same as 90 or 89. Could be "MOM and POP" gas stations are selling 89 for 92 and pocketing the differance. I saw a 20/20 special on this and it appears to be quite common. But my question is could there be another reason for the performance at a 1 or 2 octane lower? I am moving soon and there is not a sunoco in my new area. There are MB in the area and they must be running on the lower grade fuels.
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  #13  
Old 05-06-2001, 12:28 PM
mattsuzie
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Jeff,

Just so I understand correctly, are you using 89 on your 300 E when the manual/fuel guage states "Premium Gas Only"? or does your manual allow for 89.

ANother interesting thing is that when MB says premium, what does that really mean? In some countries 89 might be premium, I don't know.

The important question is what is the octance acceptability range for my 300 and 420???
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  #14  
Old 05-06-2001, 12:59 PM
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C Holmes,
Maybe the timing is off..techs out there, does this happen when the timing chain "strethes" a bit, what are the other causes? maybe the distrubuter is offset
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  #15  
Old 05-06-2001, 02:08 PM
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Ignition timing is computor determined off the crankshaft on the 103 motor. The timing chain wouldn't be involved.

What kind of plugs are you using. I have seen platinum plugs cause some weird performance problems. Plug gap too close can cause idle problems that fuel could affect.

As to the general performance issue. I find no difference in performance with different octane fuel until pre ignition occurs. Where this really matters is the new motors with knock sensors. Modern ignition systems have the ability to retime each cylinder up to 15 degrees (maybe more on some models)to accomodate the individual and combined needs. In other words if you put low test gas in the car will retard the timing three degrees, each time there is a knock on that cylinder up to fifteen degrees. By driving hard (under load)with low test gas the timing in effect can wind up fifteen degrees retarded over the same car with high test. (within 5 ignition cycles. At 600rpms that would take about one second.) BTW the timing only advances one degree per ignition cycle if there isn't a knock.
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