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1976 450SL
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34 Posts
Discussion Starter #1
Starts and drives fine after you get up to speed. It has no power, runs like a 4 cyl asian car. Runs smooth, with a little rough idle. Ive replaced the cap, rotor, plugs, OEM spark plug wires, replaced all the vacuum lines under the hood, new pedal and all linkages (pedal does open throttle all the way), the cams and chains look brand new, burns no oil, newer exhaust, no noises or pinging, Ive set timeing per specs to 0* TDC and tried up to 12* BTDC with no change. Vacuum advance does go to 35* at 2500 rpm. Ive run several tanks of gas thru it and used Seafoam to clean lines and injectors. Plugs look excellent after 1000 miles. Anyone got any other ideas where the other 200hp is...:crybaby2:
 

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1976 450SL
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34 Posts
Discussion Starter #3
LOL, well maybe it dont have 250 hp, but close. But I know my other one, a 72 450sl, feels like a V8. I can outrun this 76 from a dead stop with my V6 astro camper van. The 72 will smoke the rear tires. The 76 only will chirp the tires for a second if you rev it to 5000 in neutral and drop it in gear. I know it has to have more than 75 hp even with the 1976 smog crap on it. The guys shop next door only works on American muscle cars and his dyno says this Mercedes is putting out 72 hp (peak) @ 4800 rpm/ 124 ft lbs @ 3000. The book says the 76 is rated at 225 hp, and 280 ft lbs so my numbers are 1/3-1/2 what it should be.
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
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7,166 Posts
...The book says the 76 is rated at 225 hp, and 280 ft lbs so my numbers are 1/3-1/2 what it should be.
I don't know what book your referring to , but you certainly do have a problem, and I don't mean to make light of that.

Smooth running but no power makes me think of timing first. In the case of these ole gals, cam timing would be a good suspect. Another "cause" would/could be low fuel volume.

Hope you get it sorted out...
 

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1976 450SL
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34 Posts
Discussion Starter #5 (Edited)
I hope so too. The cams and chains are perfect. The timing is exactly to specs. I even tried advancing it more since that generally gives more power, but detonation/pinging. The vacuum advance is also right on spec. Obviously, timing was my very first suspect too. The engine has been unopened since new. I bought it from the original owner who has had nothing major needed the whole time. I know a timing chain can also jump a tooth when worn, but like I said both the chains, gears and cams look brand new. My next step is going to be looking into the fuel distributor. That was my last call since its the most expensive parts. I dont believe its the injectors themselves because it runs smooth. I would think a few bad injectors would make it sputter and missfire at all speeds, especially higher ones. It doesnt have a miss except at idle. Injectors dont all fail at the same time as a rule.

Im going by my 1976 Factory Service Manual.
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
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7,166 Posts
...like I said both the chains, gears and cams look brand new....

Im going by my 1976 Factory Service Manual.
Looks can be deceiving... Pics are available here of cams worn down to nearly no lift, and a 107 with any age on it, ie 20plus years, is suspect to sudden destruction, unless guides (and often chains) have been changed.

On the fuel distributor, pressure and volume are everything... get a set of gauges and make the measurements, otherwise you are shooting in the dark. No user serviceable parts inside the distributor is the usual caveat.

take a stroll thru the egv107 stickied at the top of the page for countless articles that you will find helpful...

in 1975, HP reporting was changed to SAE net, which results in 180-190 in most articles I perused. Moot point, as that is plenty to get up and scoot!
 

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1976 450SL
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34 Posts
Discussion Starter #8
Thanks for the info. Thats my next checks. I had a Mercedes tech I know casually come by to look, but didnt have any time for some in depth work. He miced the cam lobes and found them good and put in new oilers. He says the chain and guides are excellent. Im going to have to have a shop do the checks on the fuel pressure because I lack the proper stuff.
 

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1976 450 slc
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422 Posts
k jet is far different from djet. Critical part in the k jet system is the ease of the sensor plate movement and that of the plunger inside the feul distributor. Since feul delivery is governed by air volume being sucked into the intake, forcing the sensor plate down thus pushing the plunger in the FD up exposing more of the slits to provide feul to the injectors, IMO as was the case in my 76 450 slc years of gummy varnish build up coated the plunger in the FD in a honey like substance and impeaded the travel of the plunger and that of the fulcrum like action of the sensor plate, meaning that my car accelerated like a slug, put simply more air, more feul, but in my case the honey like varnish impeded the amount of feul because of the resistance caused by the build up.
I think in your case if spark is present and timing is right ( ignition & cam ) and feul delivery & pressure to the FD is fine then i would be looking at ease of the sensor plate movement.
 

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1976 450SL, 1945 Willy's CJ2A, 2007 Dodge Nitro
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73 Posts
k jet is far different from djet. Critical part in the k jet system is the ease of the sensor plate movement and that of the plunger inside the feul distributor. Since feul delivery is governed by air volume being sucked into the intake, forcing the sensor plate down thus pushing the plunger in the FD up exposing more of the slits to provide feul to the injectors, IMO as was the case in my 76 450 slc years of gummy varnish build up coated the plunger in the FD in a honey like substance and impeaded the travel of the plunger and that of the fulcrum like action of the sensor plate, meaning that my car accelerated like a slug, put simply more air, more feul, but in my case the honey like varnish impeded the amount of feul because of the resistance caused by the build up.
I think in your case if spark is present and timing is right ( ignition & cam ) and feul delivery & pressure to the FD is fine then i would be looking at ease of the sensor plate movement.
My 76 450sl was having a similar issue after sitting for several years. The sensor plate was very hard to move and acted like it was held in place with tar. After spraying some cleaner in there and moving it up and down for a bit it freed up and made a world of difference.
 

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1976 450SL
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34 Posts
Discussion Starter #11
If the sensor plate is the disc in the intake plenum (like 7" in diameter) it appears to work freely, but i will spray it down good with a carb cleaner. This plunger in the fuel distributor....where is it and how does an amature (to Mercedes mechanicals) access it to clean. Ive built whole cars from scratch including engines...but all US muscle cars. I did just change the fuel filter at the fuel pump. That was a 2 hour job even with the manual. Even that is alien to me. I dont know what purpose the damper or reservoir serves that are mounted beside it. US cars just have a pump and inline filter :) Thanks for the info.
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
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7,166 Posts
If the sensor plate is the disc in the intake plenum (like 7" in diameter) it appears to work freely, but i will spray it down good with a carb cleaner. This plunger in the fuel distributor....where is it and how does an amature (to Mercedes mechanicals) access it to clean...
You can remove the dist. and then the plunger, without disassembling the fuel distributor itself (something you might want to research fully if you plan on cracking it open... caveat emptor). Remove the fuel lines and then the distributor itself. Turn it over and manipulate the retainer, then carefully extract the plunger. DO NOT POLISH OR OTHERWISE SCOUR the plunger... tight clearances therin... Now you can wash the fuel distributor out with any good carb cleaner and gentle, read 40psi air to blow it out thru the fuel line ports. Reassemble and test-run... VIOLA!

Oh, and beware of small parts throughout the disassemble (filter screens, pressure regulator parts, etc).

Attached is a reference which is comparable, but not exact... close enough for government work :)

If you decide to "crack" open your fuel distributor, don't come crying back here... Parts are not readily available to the consumer. Be forewarned.
 

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1976 450SL
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34 Posts
Discussion Starter #13
Many thanks again. It looks to me like Ill let my friend do this job for me. I dont feel comfortable with all the small parts Im not familiar with. Give me an AFB carb, lol. I will spray the sensor plate down good and let it set a few hours. At this point I wouldnt be too unhappy to pay the $500 for a new/rebuilt distributor ... if....they can verify mine is bad.
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
Joined
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7,166 Posts
Many thanks again. It looks to me like Ill let my friend do this job for me. I dont feel comfortable with all the small parts Im not familiar with. Give me an AFB carb, lol. I will spray the sensor plate down good and let it set a few hours. At this point I wouldnt be too unhappy to pay the $500 for a new/rebuilt distributor ... if....they can verify mine is bad.
Spraying down the sensor plate is a waste of time... The sticky part, if it is in fact sticky, is the plunger in the FD, which the sensor plate acts upon. It can't hurt, but it won't get into the real area needed.
Now, if the sensor plate is dragging on the side of the air horn, that's another thing entirely.

Simple test. Crank the car, then shut it down. Do this next step only once or twice, as you will be dispensing raw fuel into the manifold: press down the sensor plate slowly all the way thru its transit. Did you feel resistance? You should, as residual pressure is acting against the sensor plate as it is supposed to. Let it float back up on its own... did it return fairly quickly? If so, probably free. Now do it again... less pressure this time? Surely, as residual fuel pressure is bled off each time you raise the plunger.

Now crank the car and clear out the manifold...
 

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1976 450SL
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34 Posts
Discussion Starter #15
I just thought Id finish off the thread and hopefully help someone else. The fuel distributor and components worked fine. One thing throwing me off was all the brand new plugs came out dry and clean, no carbon. It turns out the cause of my miss was a completely clogged #4 fuel injector. The plug didnt foul or burn because it was just firing off in dead space with no fuel. Cleaned out the injector with carb cleaner and air, holding it open with my fingernail until it had a nice umbrella spray pattern. Reinstalled it and immediately ran smooth as a watch. Feels like power had doubled now and smooth from idle to 80mph. Thanks for all the tips.:thumbsup:
 
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