Author Topic: W111 280 se 3.5L - Injection experience  (Read 2753 times)


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W111 280 se 3.5L - Injection experience
« on: March 11, 2020, 08:17:17 »
Hello All,

As some of you know me on the forum, I'm based in France/Besançon and I own one Pagoda 280sl 1970 Silver.
My medium term project is to buy one W111 280 SE Coupé.
My first intention was to buy one 2.8 L in order to make all maintenance easier : My Pagoda and the Coupé 2.8L share most of the same mechanical components.
But after reading some posts on internet forums, it seems that the 3.5L is more smooth and seems to offer more pleasure !
I was not aware that the 3.5 L was fitted with the electronic Kjetronic injection system.
I'm always reluctant to original electronic components in old cars : this is more difficult to maintain in  case of problem.
My question is : do some of you got real big problem/troubles with this Kjectronic injection : calculator, feeding pump, injectors, etc,...?

Thank you in advance for your feedback.

Best regards.
280 SL 1970
France / Besançon


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Re: W111 280 se 3.5L - Injection experience
« Reply #1 on: March 11, 2020, 08:51:26 »
here you'll find some information:
- Wiki W111:
280 SE Coupé          11/1967–05/1971    111.024    M 130.980 / 984    R6    Bosch Mech. Injection Pump
280 SE 3.5 Coupé    11/1969–07/1971    111.026    M 116.980 / 990    V8    Bosch D-Jetronic

- Wiki M116-Engine:

- Buyers guide from German Mercecedes Club vdh:
Conclusion: "Even if evil tongues claim the 3.5s are mummies with pacemakers, these are the models in the buyer favor at number 1 because they offer it by far most powerful and most melodious drive, who is also the most undemanding."

I hope this helps a little bit.

Aaron h

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Re: W111 280 se 3.5L - Injection experience
« Reply #2 on: March 11, 2020, 14:30:04 »
Well, first of all, K-Jetronic didn't come about until late 1974, so a W111 coupe` or cabriolet with the M-116 3.5 liter V-8 will not have K-Jetronic.  These have D-Jetronic.  D-Jetronic is all electric, and K-Jetronic is a mechanical continuous fuel injection. 

Even so, I wouldn't worry too much.  If the car you buy has been maintained well enough you won't have too much to worry about.  I have been driving D-Jetronic cars as daily drivers for 25 years.  The most expensive thing I've had to replace over the years is when my manifold pressure sensor went bad.  It was $500 USD (5 years ago).  Yes, the injectors are expensive, but they can be cleaned and brought back to life at minimal cost.  Obviously, if the electromagnet inside of the injector goes open then you have to buy another. 

The V-8 engines are more costly on upkeep all around.  They hold more oil, 8 of everything instead of 6 (pistons, plugs, wires, valves, etc), and they are very thirsty engines in that they drink a lot of gas. 

These early V-8 engines were bad about wearing their valve stem guides causing a lot of smoke from the exhaust.  A lot of people try to cheat this by replacing just the valve stem seals.  They quickly find out that doesn't take care of the smoking problem.  The original guides were too soft, but the ones made today are harder and longer lived.  Removing the cylinder heads to do this job is a $4,000-$5,000 job if you pay someone to do it, but it's worth it. 

The timing chains in these V-8 engines stretch prematurely, and the chain rails in the cylinder heads are bad about becoming brittle and breaking......which will cause catastrophic damage when the timing chain comes off or slips a tooth or two.  The rule of thumb regarding timing chains is to replace them at 100,000 mile intervals.  On the V-8 an 80,000 interval is necessary. 

The only other noteworthy issue with the 3.5 engine is all of the fuel lines/hoses going to the fuel rails and between the fuel injectors and fuel rails.  These start leaking fuel, and it happens quickly and without warning.  If the leak is bad enough it can contact the exhaust and start a fire.  Many W111 coupe` and cabriolet, as well as W108/W109 cars, have met an early death due to fire.  But don't let this turn you away from ownership.  These hoses must be checked often and/or replaced at 8-10 year intervals.  Too many people don't do this, and the resulting consequence is their own fault.  Remember that rubber has a shelf life of only 18 years.  Add in a lot of high temperatures from engine heat and the life span decreases.  The same goes with something like a windshield seal.  They have to be replaced every +/- 10 years.  Nothing rubber is ever good for the life of the car. 

Another issue that people never address is the intake manifold seals.  Not necessarily the gaskets that go between the heads and the intake itself, but the round rubber seals between the upper and lower  plenums.  Again, they're rubber.  They have to be replaced at +/- 10 year intervals.  Otherwise you'll always have fuel mixture issues. 

When all is right on a 3.5 engine they are an absolute blast to drive.  They're very quick off the line (thanks to the 4 speed automatics that start off in 1st gear), and if paired with a standard shift the experience is even better.  The fuel computers are solid state and rarely go bad, even 50+ years later.  The most important things to remember are to keep the fuel system in check, and keep the engine cool.  A 50 year old radiator may not be leaking, but the insides of them will usually be clogged. 

For your knowledge, and to simplify things, from 1969 through the end of 1974 all 3.5 and 4.5 V-8 engines used D-Jetronic, but remember that the M-110 and M-114 were also offered with D-Jetronic, too.  Volkswagen and Porsche also used D-Jetronic for a short time, as well.

In short, buy the best that you can find and afford.  You won't be sorry, and don't give much thought to the electronics being 50+ years old.  These electronics will outlast us. 


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Re: W111 280 se 3.5L - Injection experience
« Reply #3 on: March 11, 2020, 21:41:35 »
Well said AAron!
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1982 300TD Wagon turbo 4spd.
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback


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Re: W111 280 se 3.5L - Injection experience
« Reply #4 on: March 11, 2020, 22:41:58 »
Well said AAron!

Couldn't be summarized any better.
A wealth of info.
Chapeau !


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Re: W111 280 se 3.5L - Injection experience
« Reply #5 on: March 12, 2020, 02:34:20 »
Instead of asking what you do know, maybe easier to ask what you don't know.
'68 280SE W111 coupe
'60 220SE W128 coupe
'70 Plymouth Roadrunner 440+6


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Re: W111 280 se 3.5L - Injection experience
« Reply #6 on: March 13, 2020, 09:11:42 »
Hello WRe and Aaron,

Thank you very much for your information.
As I wrote in my message it would be easier for me (to standardize maintenance) to choose one W111 Coupe 2.8L instead of 3.5L. But, like some of you, I'm attracted by the power of V8.
I'll keep you informed as soon as I find the good compromise !
Thank you again for the time you spent to answer me !
Have a nice week-end !

Best regards.
280 SL 1970

Aaron h

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Re: W111 280 se 3.5L - Injection experience
« Reply #7 on: March 13, 2020, 10:25:44 »
Instead of asking what you do know, maybe easier to ask what you don't know.

Oh goodness.....there is PLENTY I don't know.  I screw things up on a daily basis, and I make mistakes every day.  My motto is "If you're not screwing something up or making mistakes on a daily basis, then you're not doing it right, and you're not trying hard enough". 

Nobody really taught me what I know.  Over the years I've been fortunate enough to have seen/owned/worked on many original low mileage examples, and in doing so my obsessive compulsiveness and annoying photographic memory filed so much away in my mind.  (believe me when I say it's a curse)  I've also amassed a very extensive collection of factory literature.  The pictures are worth every penny I've paid.  I do a lot of reading, and I guess I have the ability to easily figure things out.  It seems that no one else around me will do anything right, so I try to make things right when I can.  Though, we all know that's very time consuming and costly to make things right, and too many people in the Southeastern U.S. are far too conservative with their money to pay to have things done right.  The majority seem to want everything done cheaply.  It's sooooo annoying.  Yet, they'll go out and buy a brand new $100,000 Cadillac or GM SUV.....but when their 280SL, 600, or W108/W109 need a $1,000 or more repair they're appalled, and refuse to pay that kind of money on a +/- 50 year old car regardless of make.  I don't get their mentality.  I really wish I lived in another area of the country that have people that are excited to spend good money to restore their cars. 

Regardless, thank ALL of you for the kind words and votes of confidence.  Kindness goes a long way, and it costs nothing! 

Vincent, looking forward to seeing what you end up with.  Even if it's not a 3.5 feel free to ask about whatever it is that you find.