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my 300sd is having trouble starting. at first i thought a glow plug was going out because the g/p light would flash. but when checking the glo plugs, they were all good. then the light quit working completely yet the plugs still checked out ok. when i do a continuity test on them though, there is power for around 25-30 seconds, is this normal? also, the car does not want to turn over very easy when cold and sometimes needs a jump to spin it fast enough to start. it is taking sometimes 15-20 min. to start it in the morning if it starts at all. before this started happening, the car when at idle felt sometimes almost like it would drop a cylinder. the idle would get real rough sometimes and purr like a kitten others, but it always smoothed right out when you started accelerating. my wife is very unhappy that her benz is not well, and since #[email protected]% rolls down hill, im starting to drown in it. if anyone has any ideas id be forever greatful, thanks
 

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You are familiar with the glow plug relay? It may be your problem..BUT before reaching that conclusion, I would check the fuse under the cover of the glow plug relay. It is a silvery looking fuse and gets very HOT (so I hear), so be careful..just do NOT have the key in the ignition when you touch that fuse. My fuse was actually burnt out about 5 or so years ago, so it acted like a GP Relay failure. It sounds to me like you are describing a glow plug relay failure or glow plug relay fuse burnup.

So, roughly two years ago I had symptoms very much like the ones you describe, though I did not feel like I was "dropping a cylinder." I changed the glow plug relay and that was the cure. I would stay away from a used GP relay. If u don't know where it is...under the hood on your right, and if my memory serves, the GP relay is behind and slightly to the right of the power steering pump. There are two screws holding the GP relay onto what I think is called "the apron." (Not the kind my girlfriend cooks with. :D) It has an electrical of course...unhook your battery. Hopefully it is a fuse and not a GP relay, but those relays do go bad after awhile. GL with it, hope it works out.
 
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