280SE MPG improvment - Mercedes-Benz Forum

 
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post #1 of 10 (permalink) Old 06-21-2011, 01:38 AM Thread Starter
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280SE MPG improvment

Hello ladies and gents, I quite recently became the proud owner of a 1971 280SE something which I've wanted for years and I dearly love in every way (running or not). The one drawback I can see (besides its lack of airbags, abs, rear seatbelts, etc) is the MPG which I've read is around 11 to 12 normally and 15 at best. It's not only expensive to drive but I feel guilty when I see the exhaust rising through the rear view mirror. Any thoughts on how to improve this? I've read all the usual advice (i.e. make the car lighter, don't accelerate quickly, plan your trips in advance, don't drive period...) but are there any other methods available. It seems that the fuel injectors are adjustable? Is this possible? I'm rather afraid to touch them because of their delicate and expensive nature however if someone else has tried this and succeeded I might be able to as well. any other technologies out there? I'd be grateful if nobody tells me it's impossible as most people used the same phrasing when I asked them if I should buy one in the first place. It's been done and I still don't regret it.
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post #2 of 10 (permalink) Old 06-21-2011, 10:48 AM
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The best solution is to remove the unplug the fuel sender in the trunk and remove the rear view mirror. That should solve most of your problems.

You can look into Megasquirt injection, that might improve your mileage a little, but I really doubt it. These are thirsty cars. I would definitely NOT mess with the mechanical fuel injection if it is working properly. You can find out if it is working properly by taking it to a garage that has an exhaust gas analyzer. The gas analyzer will sniff the exhaust and tell if it is running too rich. But I think that the mileage you are experiencing is consistent with the engine in the car. My 1971 250C has the non-fuel injected engine (same engine I think without fuel injection) and gets the same mileage you are reporting in a lighter car.

You can lighten the car if you go to alloy wheels, either Bundt wheels or W123 aluminum wheels that take the same full wheel cover that the standard wheel takes. Steel wheel = 23 pounds. Bundt wheel = 13 pounds. Aluminum = 11 pounds. Big reduction in unsprung weight, will help more with handling but also some benefit to MPG. I read somewhere that reducing the mass of the wheels by this much was about the same as removing 400 pounds of weight from car. Sort of like lightening a flywheel on an engine/transmission.

Oh, by the way... you should have rear lapbelts. If you don't and want originals, contact me. Are your front belts retracting belts or Kangol magnet belts? I have parts for those (Kangol) also if you need them. There is a decent chance you have rear lap belts that have been pushed under the seat. By 1971 you should have those.

Enjoy!
Scott

Quote:
Originally Posted by Langerboo View Post
Hello ladies and gents, I quite recently became the proud owner of a 1971 280SE something which I've wanted for years and I dearly love in every way (running or not). The one drawback I can see (besides its lack of airbags, abs, rear seatbelts, etc) is the MPG which I've read is around 11 to 12 normally and 15 at best. It's not only expensive to drive but I feel guilty when I see the exhaust rising through the rear view mirror. Any thoughts on how to improve this? I've read all the usual advice (i.e. make the car lighter, don't accelerate quickly, plan your trips in advance, don't drive period...) but are there any other methods available. It seems that the fuel injectors are adjustable? Is this possible? I'm rather afraid to touch them because of their delicate and expensive nature however if someone else has tried this and succeeded I might be able to as well. any other technologies out there? I'd be grateful if nobody tells me it's impossible as most people used the same phrasing when I asked them if I should buy one in the first place. It's been done and I still don't regret it.

Currently: 1967 250 SL, 1963 220Sb, 1965 300SE Lang, 1971 280SE parts car, 1972 Alfa GTV, 1965 Alfa Duetto, 1993 BMW R100R
Past: 1971 250 C, 1985 300 TD, 1967 250 S, 1968 280 S,1981 300 D, 1982 280CE, 3 Facel Vegas, Borgward Isabella Coupe, Alfa 2600 Sprint, Volvo P1900 (yes), numerous less interesting Volvos, ...
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post #3 of 10 (permalink) Old 06-21-2011, 11:39 AM
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langerboo congrats on your (new to you) rig. You have a buautiful car. i assume this is a second car and not a daily driver because she is more of a garage queen, sunday drive, special occasion / show off special car. If i am in error and you are using the 280 SE as a daily driver Then i would go get a 123 diesel sedan they are failrly inexpensive have an abundence of avaliable parts and with moderate care will run damn near forever (they used 123 diesels as taxi cabs in europe and other countries back in the day.
The 280 SE should be a drive it for fun and dont wory about the fuel mileage kind of car. The better she loks the more compliments you will get. You own a legend. If I remember correctly the 108 / 109 were still hand built cars.
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post #4 of 10 (permalink) Old 06-21-2011, 09:40 PM
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SCoot, I am interested in getting new belts for my 72 280SE 4.5. The front ones are frayed badly, inbox me if you can.
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post #5 of 10 (permalink) Old 06-23-2011, 06:00 PM
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Great way to improve the gas mileage is to stare at it in the garage and make car running sounds...jk. Enjoy the car and car a siphon pump...lol.
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post #6 of 10 (permalink) Old 06-28-2011, 01:52 AM
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If your 280 is K-Jet (mechanical injection), which I fairly doubt, first thing you should do is to check for damaged vacuum hoses. K-Jet relies on vacuum levels to control amount of fuel injected. I used silicone tubing to join fractured plastic hoses and some cases to replace them.
Unmetered air leaks are common around injectors on all Mercs of this age and reseal is cheap.
There is always a possibility for PO or PO's mixing up the engine management things.

IMO, 15mpg should be usual city/freeway mixed mpg value but you should be able to achieve, with gentle driving on freeway, much better than that, like 20mpg. Unless the engine internals are worn (like blue or white smoke) you have fuel management issue.

To summarise, if you have some elbow grease, you can be directed. More replies you will achieve on W116 forum. Otherwise search whole forum for recommended trustworthy Merc grease monkey.

.
Vitamin C for SL... the SLC
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post #7 of 10 (permalink) Old 06-28-2011, 04:05 AM
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With the help of a forum member we discovered a disconnected vacuum hose and running rich. this helped get the car running in better tune. timing was also adjusted. I also had a new exhaust fitted to replace my loud old non-stock one that was not even bolted at the manifold.

I went from 12/13mpg to 16mpg. a big difference to me

i have a '68 280se straight 6. you should have rear seat lap belts also, mine does. yours should be under the seat hiding
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post #8 of 10 (permalink) Old 07-02-2011, 12:06 AM Thread Starter
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Thank you for these replies! The best I was expecting was Dylan1471's answer which I'm currently using until I can install the new water pump. I did check under the rear seats and found the seat belts! Needless to say it felt liek a mid-june Christmas. The Fuel injector is electronic not mechanical but I'll certainly look over them anyway. Thanks!
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post #9 of 10 (permalink) Old 07-13-2011, 04:24 AM
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Quote:
Originally Posted by Langerboo View Post
Hello ladies and gents, I quite recently became the proud owner of a 1971 280SE something which I've wanted for years and I dearly love in every way (running or not). The one drawback I can see (besides its lack of airbags, abs, rear seatbelts, etc) is the MPG which I've read is around 11 to 12 normally and 15 at best. It's not only expensive to drive but I feel guilty when I see the exhaust rising through the rear view mirror. Any thoughts on how to improve this? I've read all the usual advice (i.e. make the car lighter, don't accelerate quickly, plan your trips in advance, don't drive period...) but are there any other methods available. It seems that the fuel injectors are adjustable? Is this possible? I'm rather afraid to touch them because of their delicate and expensive nature however if someone else has tried this and succeeded I might be able to as well. any other technologies out there? I'd be grateful if nobody tells me it's impossible as most people used the same phrasing when I asked them if I should buy one in the first place. It's been done and I still don't regret it.
congrats dude, please post the pictures of your 1971 280SE I will be eagerly waiting for your next post.
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post #10 of 10 (permalink) Old 07-13-2011, 03:46 PM
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You should have the Bosch D-Jetronic fuel injection system (D-Jet). These things are mainly controlled by vacuum and two temperature sensors. One on the air cleaner provides the 'fine tuning' of the fuel/air mix, and one or around the water pump provides the main input to the ECU.

There are a few other components that are involved, but these are the inexpensive (for Mercedes values thereof) places to look. Vacuum lines, and temp sensors and associated wiring. The pulse generator (injector points) and MAP (Manifold Absolute Pressure) sensor are two that get REALLY pricey.

Google Bosch D-Jet and look around for an article or two on the theory. you might just see something that will help you out.

Good Luck
Scott

Remember: It's not just a car. It's an Adventure.
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