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Old 09-25-2003, 09:29 AM
Posts: n/a
Fuel enrichment adjuster?

This was a bit od so I thought I'd share it. My 1988 300e
has been a having a bit of a starting problem. When I turn the
key, it takes about six or seven cranks to before the engine
turns over. Spark plugs, wires, cap and rotor are new and OEM.
Fuel is top grade, from new gas stations only. Fuel filter
is new also.

My tech said it may be the fuel accumulator, but before we go
that route, he adjusted the fuel enrichment because it sounded
a bit lean. First he tried doing it by inserting a long thin screw
driver down through a hole in the air filter housing. But then
he removed the housing because he could not reach it.

Now here's were it gets a bit wierd. My tech has worked on
MB for 25 years, so I assume he knows what he's doing. After
he removed the air filter housing, he took a grinder and grinded
off the top of a small pyramid like structure. He then inserted a
screw driver and ever so slightly turned (or bearly put pressure
on) the screw mechanism inside the decapitated pyramid.
The car has smoothed out. Starts are no more than three cranks
and the idle is smoother too.

Not that I'm complaining, but I just found it odd that the small
sealed pyramid structure contained the fuel enrichment
adjustment that had to be grinded off. Has anyone else had to
do this or has this guy just made my car into a FrankenBenz?

BTW - my tech also said not to fanagle (actually I think
he used another 'F' word') with the adjustment. After what I
saw him do, fanagling is not part of the equation anymore.

Any thoughs on this?


Last edited by bluebenz; 09-25-2003 at 01:10 PM.
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Old 09-25-2003, 12:55 PM
sixto's Avatar
smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 18,745
The mixture asjustment screw is sealed from the factory. An experienced person can tweek it by feel. The rest of us need at least an ammeter, duty cycle meter and specs to set mixture properly.

I've never done this but from what I read there's a part that replaces what you have to break off to get to the adustment screw. It's available in FastLane, I think.

95 S420
91 300SE
87 300SDL
83 300SD
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Old 09-25-2003, 01:12 PM
Posts: n/a
Thanks Sixto,

I appreciate your reply.


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Old 09-25-2003, 02:45 PM
Registered User
Join Date: Mar 2003
Location: Southern California
Posts: 2,010
I would not trust ANYONE to diddle with the idle mixture screw unless they were observing the duty cycle to be sure it is in the proper range. This procedure has been thoroughly outlined on this forum and many, including me, have run the test, so a pro should be able to do it too.

The 103 engine is known to require what some might consider to be excessive cranking to cold start or start and quit, requiring a second try. This is particularly noticeable in the summer when
"cold" starts are done at or near room temperature. The cold fuel calibration is lean at about 70F, because this is the cold start temp for emission certification. At colder temps, say 50 or below, the cold start behavior is usually much better.

The acculumator can be checked by installing a pressure gage and observing the behavior of the fuel pressure after shutdown. Assuming no external leaks, a rapid fall of pressure could be an indication of a malfunctioning fuel accumulator or an internal check valve.

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