My 300SE Doesn't Like Mondays - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 12-23-2012, 08:30 AM Thread Starter
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Date registered: Dec 2012
Vehicle: 1985 190D 2.2, 1990 300SE, 2008 E350 wagon
Location: Los Angeles
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My 300SE Doesn't Like Mondays

I wanted to share a recent experience with my 1990 300SE with an M103
engine. Typically I drive it to work, then home, five days a week, and it
then sits over the weekend until Monday rolls around again. A few months
ago, I started having a strange symptom - only after the car sat all
weekend - in that after a brief uneventful warmup period of about ten
minutes, the car would begin to hesitate, stall, and generally behave badly
whenever a load was put onto the engine. And then, after ten minutes of
frustration, the car would then drive normally - until the following

I was unable to identify the source. Internet searches came up with very
little concrete suggestions, and without success I changed the o2 sensor
and the six fuel injectors. I ran more than one container of Chevron
Techron in hopes of freeing something up.

I left it with my mechanic for a couple of weeks so he could put his
testing equipment on the car when the problem surfaced. He strongly
suspected the coil, which he said could fire a weak spark during those
times, and we changed the coil and the symptoms went away. As I was
picking up the car, I asked if he had ever checked the EGR valve, and we
put a Mighty Vac onto the port, and indeed it was leaking. Before driving
away, he replaced it with another used non-leaking EGR, and I was on my
way. The real test will be on Monday, but I'm thinking it's good.

I would be curious to know if anyone else has had a similar problem and
what they did to fix it.
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post #2 of 3 (permalink) Old 12-23-2012, 09:36 AM
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Date registered: Dec 2005
Vehicle: W211 E320 Bluetec R129 SL500 - $1300 car ........ Ford F350 6l
Location: CA Bay Area
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I have similar problem with my Ford Powerstroke that I don't drive very often. Usually it starts right away, but occasionally when it sits over a week it will take lot of cranking to start and it will run rough for some time.
Those things are usually associated with fuels system loosing the prime. If your car is having mechanical fuel pump, you might want to replace check valve. On electrical pumps you can prime it 2-3 times by turning the ignition on/off.
Easy way to troubleshoot is installing pressure gauge on the fuel lane.
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post #3 of 3 (permalink) Old 02-28-2013, 03:02 PM Thread Starter
BenzWorld Junior Member
Date registered: Dec 2012
Vehicle: 1985 190D 2.2, 1990 300SE, 2008 E350 wagon
Location: Los Angeles
Posts: 8
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Quoted: 0 Post(s)
(Thread Starter)
An update on my original mechanic changed my coil as written above, which ultimately made the car run marginally better. I still experienced extreme hesitation though after a long weekend, and it deteriorated to the point where my car would die in heavy traffic.

So, back to the mechanic it went. After the coil, the next item up the wire is the EZL controller module. This part was changed with a used one for about $250 or so, and it has now been close to three months with no more stumbling problems. So, in summary, the spark was weak, and it took a different EZL (and maybe a new coil too) to solve it.

I still have the old EZL floating around in the back of my trunk. Someday I plan on opening it up and seeing if I can identify the failed part. I'm thinking it could be a capacitor, but won't know until I open it up. I fear it is sealed shut with epoxy, but if I make any headway I will post a reply to this post.
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