76 300D cold start issue. - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 06-07-2015, 06:55 AM Thread Starter
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76 300D cold start issue.

First off I'd like to introduce myself, I'm Justin and it's nice to meet everyone.

I recently acquired a 1976 300D w115.
51,000 original miles
Very well taken care of.

When I purchased it the car ran great, started fine ran all day etc. Everything on it worked aside from the glow plug light and clock. I was told the light was out due to a blown bulb. Which I haven't yet replaced, I just count to 40 haha.

Then one day it was hard to Start, let it set and cranked away and it fired up. About a week later it wouldn't cold start for anything! I ran the battery dead and even melted the battery ground cable! =[. So I wrapped up the cable and charged the battery after two glow cycles it fired up and ran. But I think I now have a vacuum leek somewhere seeing as the cruise control has stopped working and you have to idle it up a little then turn off the key to stop the engine. That being said, after the engine is warmed up it fires right up without the glow plugs no problem and runs fine, shuts off etc.

I assume the glow plugs are working because the resistance rail gets glowing red hot after 30-40 seconds. I assume if there was a problem with them this wouldn't happen seeing as they run in series.

So, is it possible they are just fouled out? Causing them to not work properly on a cold start? Or is there some other problem I may be over looking?

Also I might add, I assume fuel delivery is not a issue seeing as it runs strong and normal after and if it fires up.

I also noted that while cranking the engine on a cold start it will try to catch and fire randomly. Some times it catches and starts, other times I just kill my battery lol.
Also you can see and smell diesel vapors coming from the exhaust pipe.

Also another thing I noticed about the above mentioned vacuum leak. Would this make cold starting the car difficult? Could I hook a vacuum meter to the vacuum pump to see if maybe its just not producing enough vacuum? If so where should it read?

Any thoughts or suggestions would be greatly appreciated.

Thanks, -Justin
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post #2 of 3 (permalink) Old 06-07-2015, 06:59 AM Thread Starter
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One thing I forgot to mention, please excuse my ignorance on this car, because I'm sure there will be plenty of it lol. This is the first diesel I've ever messed with. Up until now I've strictly been a gasoline mechanic.
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post #3 of 3 (permalink) Old 06-09-2015, 01:22 PM
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As cheap as they are, I would replace the glow plugs anyway, just to be sure.
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