Hello, I have a low miler 300SE, and its got a misfire when warm.

When the engine is cold, the car starts and idles like normal, drives good and seems to have no issue, when it's warm, it runs slightly uneven and sometimes it misses, if you are driving at high speed and let go of the throttle to slow down, it will start to miss when accelerating again.
When at idle, it will run eneven, and miss after 5-10 seconds, it just misses a few strokes, but it varies. If you hold the brake and put it in D, it will run at about 550 rpm and miss even more. The exhaust smoke is too much grey too.
On rare occasions, it have not started when warm, I had to wait till the engine cooled down a bit. I have changed the coolant sensors, but I'm not sure if that solved the problem, it's cold weather outside these days.

I have changed all parts for the ignition, everything is correct to the m103. New EHA adjusted by MB too.
I think it can be one of these parts that can make it run like it does

-Injector is leaking (IR thermometer at cylinder 1 and 4 show lower temperature then the others)
-Fuel accumelator that can not adjust the pressure when lowering speed
-Plugged fuel filter (time for change)
-OVP relay starting for fail (mine is from 89)
-Voltage regulator (I heard they can cause issues like this)
-Running too rich (It did get Co adjustment when MB replaced the EHA, but the engine was missing still)
-Engine timing, the light showed at idle 1tdc, when at 3000rpm, I think it showed 30, can't remember.
I just recently changed the valve seals that were bad, I noticed the engine used oil, and the spark plugs were black. Although replacing them did not fix my problem, it did help allot. It solved my hesitation issue, and gave some freshness to the engine.

Any of you guys had this problem before? Any help would be much appreciated

Sondrusen, if the fuel filter has not been changed in the last 60,000 miles it's time to replace with a Bosch fuel filter.

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Fred Hoelzle

What plugs have you fitted to the engine? Must be none resister type .
Check all fuses ,replace if made of white metal for some made of copper .or brass .
Ceck all vacuum pipes , for splits , cracking .
Next check all earth points they will need cleaning and a little greas on the body ,fix them back on..
As for OVP relay look at the fuse or fuses as some did have 2 , remove it and give it a shake .If it makes a noise it shot .replacment or repair it .

From the thread title..."no start when warm".

My guess would be the accumulator.

New fuel filter is not a bad idea, since you need to pull the whole fuel pump/fuel filter/accumulator assembly in order to get to the accumulator.

http://s1377.photobucket.com/user/lesterl/media/Fuel%20Pump%20Misc%20020517A_zpscghizk54.jpg.html?o=0

I am very known with m117, m103 etc, so everything from plugs and so on is within spec. But yeah, i think the accumelator is one of the main culprits here. Going to replace filter and install a higher efficiency coil now(you can then run different plugs) Altough I don't think the coil has anything to do with this.

Out of curiosity, how is the overall health of the ignition system? Last time the cap/rotor were changed? Brand?

It could be worth your time to test your spark quality, get a spark tester and determine if you have good, consistent spark.

I'll offer a dissenting opinion on the fuel accumulator. While it can cause a difficult time starting when warm/hot, the car SHOULD start if you crank long enough and the fuel pumps rebuild pressure. Once started, the accumulator shouldn't have any real bearing on the engine's operation, especially at idle. You shouldn't be running rough or missing out if the accumulator is bad.

I bring up spark because I went through a similar saga in my SL. Was a PAIN to restart hot/warm, and always seemed to have a really crappy/lopey idle when hot, sometimes getting to the point that it acted like multiple cylinders missing.

I did replace the accumulator (it was definitely bad) and it did help with the hot starts, however it did nothing about the poor running. Eventually one day the car simply failed to start. Testing showed no spark at all. EZL failed. Replaced the EZL with a junkyard pull and the difference in how the engine ran was night and day from how it had been behaving before. The rough/lopey idle when hot disappeared and has been gone ever since.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)