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Perlmuttgrau 300SEL
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Discussion Starter #1
I still, after much umming and ahhing have a hot start problem. Am thinking it could be leaking injectors. The car starts *almost* perfectly in the morning, doesn't need throttle but has a second or two of roughness; but after shut down,

1-2mins, starts totally right, no rough idle, no nothing starts like a BRAND NEW CAR

5-10mins, starts to get a little rough for one second, but doesnt need throttle

12-15mins, becoming a bastard, needs throttle, splutters and chucks, but starts.

20mins plus: total ass clown, Needs three or for goes for 5 seconds at a time, splutters for yonks, runs on 4/5 out of 6 cylinders for 4-5 seconds, then comes goodand idles like it never had a problem for as long as i drive it.

Stop the engine, and its the same cycle all over again, unless you leave it till tomorrow morning and then its back to slight little rough idle at start, no throttle needed and so on as the day goes.

300SEL euro, New O2 sensor, New Cap/rotor/plugs. New EHA, tuned on a bosch scope, new fuel pump/filters/relays and within service specs/ 98 octane fuel only....

*******H E L P************

Could it be the injectors slowly leaking under pressure after shutdown? causing the fuel to vaporise at it contacts the hot piston/pools in the dish of the piston as it cools...Im assuming that as time goes by, more and more fuel (until the pressure behind the injectors eases up) is leaking into and vaporising in the chamber, with no where to go (I once took a spark plug out of the engine when it was still quite warm and heard gas hissing out,)? and is the fuel returning to a liquid state as the ambient temperature inside the cylinder/combustion chamber comes down?

Thanks for any input. Cheers.

Im stuck, my mechanic reckons its the heat (38degrees cesius up here EVERY DAY), but have met other guys with m103s and 5 litre motors who dont have this problem at all......interesting one eh?
 

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560sel
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Aaron I have a 560sel. With the V8 the problem you describe is almost always caused by a bad fuel accumulator. If you have a fuel accumulator it's #1 to check.
 

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Depends on the day!
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It does sound accumulator ish.. When the car is being particularly hard starting try holding your foot to the floor. If the injectors are leaking down the addition of air will help bring the a/f ratio back in order quicker.

Let us know:)

Jonathan
 

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Perlmuttgrau 300SEL
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Discussion Starter #4
okay.... so we pulled the injectors, pressurized em, no leeks. What we did find is the plugs in cylinders 3 and 6 are splattered in oil. Severely coked up, almost bridged, although cylinder three was three times as bad as six. The others all showed appropriate wear for plugs with less than 1000miles on them. Yes, only 1000miles

Why i hadn't noticed this? only changed plugs once before, all plugs look pretty filthy, so I just changed em (this is last year some time by the way!)and continued on my way.

So it would appear that there is a valve stem seal problem in those two cylinders at least, and after replacing the plugs, we idled the engine enough to get hot plugs, pulled the ones from three and six, and they they showed signs of oil.

So, through the power of deduction, i figure that:

The engine is a little dificult to start in the morning because the oil had time to drain off the plug, but has left enough behind to cause the SLIGHT roughness at start up.

When I start the engine immediately after shut down, it runs fine because the oil has been burnt of the plug and there is nothing there to cause a lack of sparking.

As time goes on (20/30 mins plus) the oil from the hot engine continually drips down onto the plug and causes the misfiring????

Also noticed that after driving the engine friom the mechanix to a mates place (1 mile), and leaving the engine for about 1/2hr, it started up quite a bit easier than normal....didnt need throttle, but still only ran on 4/5 cylinders for a few seconds, then came good again.

Talk about jumping to conclusions eh? I know I know, just that we've tried everything else (including the accumulator!!) so I am really hoping that this solves it...really hoping!!
 

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Do you have a test bench for the injectors? How long did you leave them under pressure?

I Hope that works for you! I'm not at all surprised that you are seeing oil on the plugs, the valve guides in MB heads are quite soft.

Jonathan
 
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