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  #1  
Old 01-27-2009, 12:38 AM
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Hello! Looking for some info(W126)

Hi! I just purchased a 1986 560SEC from a friend of mine and need a little bit of help diagnosing somethings with the car.

First off, could someone link me too a good source of reading pertaining the fuel system on the car? I would like to familiarize myself with the fuel injection and emission system of the car!

And which leads into my current problem. I'll give you a little background info. I bought the car in LA, and drove it back to the bay area, which was a bit more than 300 miles. It got great economy getting back, easily over 200 miles to the tank(the speedometer does not read so I couldn't calculate the mileage heh). But when I did return home that night, during some street driving, i noticed the 02 sensor light on the dash became illuminated.

Throughout the next couple days driving the car, the fuel economy has been way less than stellar(and I definitely don't think its due to the huge V8 under the hood) and the light keeps coming back after 5 minutes or so on the road, and sometimes will turn off, and re-appear in the same trip. I have driven less than 160 miles and from a full tank on saturday, to today I have around a quarter tank. I don't think that is normal, and I did not hoon it around either, drove it like a grandma. So I believe the possible super rich condition and this 02 sensor light are hand in hand. The car did have its 02 sensor replaced and tuned according to my knowledge previous to my purchase.

Anyone have any insight? Thanks!
-Kyle

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  #2  
Old 01-27-2009, 01:05 AM
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The FI system on these cars is basically CIS with some electronics wrapped around it. The ECU is fused at the OVP, OVervoltage Protection relay which is mounted between the two firewalls and has a red top and a clear hinged top and a fuse or two. The ABS computer is also mounted between the firewalls and is not to be confused with the ECU behind the passenger kickpanel.

This page will give you a start on the CIS-E system

http://www.landiss.com/mixture.htm

There are many posts on this system. Be aware that the CIS fuel distributor and the feedback pot are getting long in the tooth and are prone to failure/wear.

560sec.com is now under construction and the buyers guide is N/A.

There are lots of good posts on what to check including the DIY section. Check benzworld.com and the MBCA forums as well.

http://en.wikipedia.org/wiki/Mercedes-Benz_W126

The CE light is really just for an alert to change the O2 sensor. I really suggest you get the service CD's usually available on Ebay.

http://www.classictechlit.mbusa.com/MB/cstmsearch.asp?MYID=1040&SDID=1332&MDID=1237&ENID=1069&catalog_name=Retail

the technical data book is also good.
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Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

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  #3  
Old 01-27-2009, 02:01 AM
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The gasser W126 has a 23-24 gallon tank I believe. 200ish miles to the tank is BAD. Thats hovering around 10mpg or less!

However, the 560 is a VERY hungry engine, and will likely not do much better than 12 city 14-15 highway (on a good day driven gently)
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  #4  
Old 01-27-2009, 02:54 AM
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I'm pretty sure it may have to do with the fuel mixture, its the best lead I have so far. Is that something designed to be commonly adjusted at set service intervals? The car does give off an unburnt fuel smell at times, usually noticeable at slower in town cruise speeds.

Or am I taking this the complete wrong way? I think the best way would be to replace the speedometer sensor on the trans and get that speedo working again and start calculating!

Edit, Also, how does the lambda circuit affect the engines fuel mixture on this engine?
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  #5  
Old 01-27-2009, 09:35 AM
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There's another website you might find helpful: MBcoupes.com. There are some very nice SECs in their gallery.
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  #6  
Old 01-27-2009, 12:16 PM
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Oh goodness, what a neat website.I wish I had a camera to show off my car, I'm so proud of it!
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  #7  
Old 01-27-2009, 07:30 PM
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You might find it worthwhile to join the MB Coupes mailing list.

There is an archive, but it gets convoluted to try to dig through it in web form.
If you end up with a question that you can't find in the forums here, there are a number of people who will chime in on the mailing list as well.

That being said, many of us are lurking in the forums too, just who knows if we ever see all the interesting questions!
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  #8  
Old 01-27-2009, 09:14 PM
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It would REALLY!!!! help to know the year of your SEC. I have both a 560 SEC and a Euro 500 SEC and they both will do approx 400. miles or darn close per tank of gas.
I think you need to take the car to a trusted Indy and do a Post Purchase Inspection. Money well spent. instead of GUESSING what it wrong and then throwing dollars at it. You will end up spending way more that the hour or so fee for the PPI, and besides you will have a solid baseline to base the car on.
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Last edited by Chadahar; 01-27-2009 at 09:19 PM. Reason: Speeling..oops! Spelling
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  #9  
Old 01-27-2009, 10:30 PM
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I would love to find some good reasonable mechanics in the Bar Area! There are so many German mechanics around here it makes it difficult.

Anybody in the Bay Area looking to maybe give an enthusiastic learner/enthusiast a helping hand!

Tomorrow I'm going to receive the manuals on CD, so its time to start reading and doing some self diagnosing.
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  #10  
Old 01-28-2009, 12:24 AM
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Quote:
Originally Posted by pawoSD View Post
The gasser W126 has a 23-24 gallon tank I believe. 200ish miles to the tank is BAD. Thats hovering around 10mpg or less!

However, the 560 is a VERY hungry engine, and will likely not do much better than 12 city 14-15 highway (on a good day driven gently)


Nah 560s can and do get better than that, mine does. I got low 17s freeway only from Dallas to Houston. Avg speed was 65-70mph area.

City is usually mid 13s.
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  #11  
Old 01-28-2009, 12:49 AM
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I could totally figure it all out if my speedometer worked haha, Johnathan said he thinks the sender from the transmission is shot, so I need to run to a junkyard and see if I can find one. I assume that part in question could be interchangeable between the coupe and sedan? Also, how many different types of transmissions were used in the W126 chassis? Would a 420SEL use the same transmission as my 560SEC?
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  #12  
Old 01-28-2009, 08:08 AM
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Both the SECs and SELs of model years 1986-1991 used the 722.3 AT in several variants. Not sure if that would affect interchangeability. BTW, it's too bad you didn't take the time while you were in So Cal to take the SEC to Mr MB in Tarzana for a thorough inspection. There's no better MBz technician anywhere.
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  #13  
Old 01-28-2009, 12:40 PM
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Quote:
Originally Posted by Hit Man X View Post
Nah 560s can and do get better than that, mine does. I got low 17s freeway only from Dallas to Houston. Avg speed was 65-70mph area.

City is usually mid 13s.
What fun is 65mph in a 560?
__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 102k - mine - (OC-104,600)
'17 Metris(VITO!) - 26k - wifes (OC-25k)
'09 Sprinter 3500 Winnebago View - 57k (OC - 63k)
'13 ML350 Bluetec - 73k - dad's (OC-75k)
'01 SL500 - 92k(km) - dad's (OC-94,000km)
'16 E400 4matic Sedan - 122k - Brothers (OC-125k)
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  #14  
Old 01-28-2009, 02:35 PM
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JimB has an SEC and used to live in SF. He's all over this forum. e could give you all the information you want about resources in your area.

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" We have nothing to fear but the main stream media itself . . . ."- Adapted from Franklin D Roosevelt for the 21st century

OBK #55

1998 Lincoln Continental - Sold
Max 1984 300TD 285,000 miles - Sold
The Dee8gonator 1987 560SEC 196,000 miles - Sold
Orgasmatron - 2006 CLS500 90,000 miles
2002 C320 Wagon 122,000 miles
2016 AMG GTS 12,000 miles
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