W108 - idle/warm start problem - Page 2 - Mercedes-Benz Forum

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post #11 of 13 (permalink) Old 03-30-2014, 12:06 PM
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Date registered: Feb 2012
Vehicle: 2006 C230 Sprots V6, 1972 280 SEL 4.5
Location: San Francisco, Ca
Posts: 39
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Originally Posted by Oskar View Post
well, as promised - here is the update

pulled out slide, checked it in hot water - closing at 70 deg C. - works
new fuel filter - fixed a leak in the return line as well
- problem still exists
replaced vacuum line from distributor via AC valve to throttle
- no change
replaced lower seals on the injectors
measured fuel pressure - too low just 1.2 bar instead of 2. adjusted fuel pressure. Pressure holds.
car is way too rich now. the adjuster for idle emission is on left(lowest) setting
Lambda reads .75 to 0.8 at 75 mph cruising ( I used a innovate LC1 at the tailpipe )
the manifold pressure sensor comes to my mind - replaced it with one from a parts car.
Bingo!
idle (air) adjust nice now, idle speed emission adjusts nice.
Lambda when accelerating is around 1. Even fuel cut off works ....
Engine is running now like a MB V8 should run

Thanks for all suggestions - got me on the right track

I bought the car as an restoration object, half a year ago. Seems to me someone tried to compensate running too rich by lowering the fuel pressure

Thx again
Oskar
Hi Oskar,

Would you happen to have a photo of your M117 engine? I'm trying to determine if my problem is the vacuum lines from throttle body to the distributor diaphragm. If all else fails I will consider replacing my MAP sensor. The photo of your engine will help me determine if I have my vacuum lines installed wrong. Thanks in advance
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post #12 of 13 (permalink) Old 03-31-2014, 08:51 AM
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Date registered: Nov 2012
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common problem , when you shut the engine off hot , if you watch the temp gauge , after a few minutes , the temp goes higher in engine .since this efi system is temp controled , the temp sensor on top of intake manifold send a lean signal , so if the fuel mix is on the lean side to start with , you end up with a over lean condition .the fix is to set the mix richer , like 3 % HOT at 2500 rpm .if you unplug the air filter temp sensor [ to test ] , this will richen the mix , the engine should start up better .
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post #13 of 13 (permalink) Old 03-31-2014, 10:09 AM
BenzWorld Junior Member
 
Date registered: Feb 2012
Vehicle: 2006 C230 Sprots V6, 1972 280 SEL 4.5
Location: San Francisco, Ca
Posts: 39
Mentioned: 0 Post(s)
Quoted: 1 Post(s)
Quote:
Originally Posted by agillot View Post
common problem , when you shut the engine off hot , if you watch the temp gauge , after a few minutes , the temp goes higher in engine .since this efi system is temp controled , the temp sensor on top of intake manifold send a lean signal , so if the fuel mix is on the lean side to start with , you end up with a over lean condition .the fix is to set the mix richer , like 3 % HOT at 2500 rpm .if you unplug the air filter temp sensor [ to test ] , this will richen the mix , the engine should start up better .
Unfortunately for me, my engine is running rich. Way too rich that I just blew out my muffler. I definitely need to further adjust the air/fuel ratio to run leaner. Prior to blowing the muffler, my W108 was running extremely well. Aside from the slight fuel smell (from rich exhaust fumes), the engine was performing flawlessly with strong acceleration. As soon as I replace the muffler I'll work on the a/f mixture. Lucky for me I have access to a gas analyzer.

Thanks for the advice.
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