I read a few previous posts on the topic but they didn't quite cover this. I just bought an '87 420SEL from a friend (I've been eyeing it for about 5 years) who said she's been using nothing but regular unleaded in it for the 100,000 miles or so she's owned it (2nd owner). It's at 257,000 now and seem to run okay (rough idle but I'm told it's something that needs replacing in the injection system) at speed.
Since there is a very clear note on the speedometer to use premium unleaded, that's what I'm doing now. The question is, what effect would all those miles of regular have been? Am I helping it at all by using premium or is it likely carboned/gunked up from the low grade so that it makes no difference?
Well your car is actually ruined. It will never work properly so you may as well dismantle it and send each one of us here on this forum whatever parts we ask for.
Kidding aside, I think you need to tend to the rough idle as soon as you can. Search the forum for remedies, you will find a wealth of information here.
Oh, welcome newb
Some number of years ago the federal government passed a law requiring that any car sold in the US market is required to run on 87 octane and suffer no ill effects. I don't remember what year it was however it was prior to 1987.
That's why MB installed the damn resistor in the first place. So the engine would run on low-octane because of cheap-ass people who just can't afford (???) premium gasoline for their very expensive car.
Not poking fun at anyone. I never understood the whole "oh, I can't afford premium gas" spiel. What's the max difference in regular to premium, like $4 a tank? A shitload of people blow way more money than that on cigarettes or coffee, in one day!
IMO, start using premium. And get that rough idle looked at soon.
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"Imagination is more important than knowledge"
yeah well it's a bitch when i ONLY use premium regardless of requirments, and smoke a pack every 24 hours, aswell as startbucks at night and rockstars in the day...
premium is a must, not only for limitations of detonation but also because it's a bit more pure and therefore, cleaner..
Vehicle: 1985 500SEC, 1991 190E 2.6 (50k original miles)
Location: Los Angeles
Posts: 9,947
Quote:
Originally Posted by Bill Tubbs
I read a few previous posts on the topic but they didn't quite cover this. I just bought an '87 420SEL from a friend (I've been eyeing it for about 5 years) who said she's been using nothing but regular unleaded in it for the 100,000 miles or so she's owned it (2nd owner). It's at 257,000 now and seem to run okay (rough idle but I'm told it's something that needs replacing in the injection system) at speed.
Since there is a very clear note on the speedometer to use premium unleaded, that's what I'm doing now. The question is, what effect would all those miles of regular have been? Am I helping it at all by using premium or is it likely carboned/gunked up from the low grade so that it makes no difference?
Welcome to the forum. To include your car mod. and location makes it easier for members to offer advise. If you don't have one yet, Mercedes Benz at www.mbusa.com has the official 2 CD service manual for $ 20. Outside the US the thing costs up to five or six times that. Check out MBL87560SEC's post in the DIY thread above. It has the link/information how to order, and how/with which free Steve Nervig index to download to HD. You can also type your question into the 'search this forum' box on the top right. It will get you all archived post re. your problem. You might try the Russian MB site. Don't put in a mod. or vin, click on cars and scroll down, until you get to yours. Good luck. http://www.detali.ru/cat/oem_mb.asp
ok, here is the newbie question. What's up with the resistor R16/1? Since I use premium gas anyway (1984 500 SEL grey market, 184,000 mi, idle ok, a little shaky at stop lights (motor mounts/). Should I remove thie resistor for better performance? Was it added to my car for us compliance (has passed emissions test in FL after failure?) if added jjust for cheaper gas, I'll ger rid of it if there is a reason to do so.
I'm lucky, my car only requires 81 octane (not a Mercedes) but I wonder if it would do ANY good at all to run 91? I was told it's not worth it, if the car only requires 81... i guess the only outcome is a little bit more horsepower?
no power increase. higher octane will only benefit you with raised compression or more aggresive ignition advance. aside from that, it's just throwing money away. the only potential benefit is keeping the fuel system a bit cleaner, but the price difference doesn't justify it. oh yeah, do you work today? i was thinking about going down to German Car Service or whatever that place is called on scottsdale road.
Thanks all, for the support. I'll have to ask the PO why on earth she was running regular all this time. I'll bet her local Mercedes mechanic (former dealer mechanic) told her it could. My SAAB Turbos have a computer chip that automatically adjusts timing/retard, etc. for lower grade fuel that is found in various parts of the world. I didn't know if the Mercedes did the same thing or not. Apparently not.
I have several 'fun' cars, including my vintage SAABs and an '88 BMW 528e, so I tend to drive them on a day-to-day basis and run the 420SEL as a treat every other day or so. That way I don't sweat the fuel cost so much
The problem I have with the idle is that it's a little rough and feels like it's missing. Sometimes it doesn't start right up and needs a little finesse on the accelerator to get it going. But anything above idle speed if just fine and it rides like the battlecruiser it is ... very nice!
I never understood the whole "oh, I can't afford premium gas" spiel. What's the max difference in regular to premium, like $4 a tank? A shitload of people blow way more money than that on cigarettes or coffee, in one day!
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