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hi, I just got this 84 300D, and as everyone knows, whenever you get a new-to-you one of these, all kinds of weirdo problems present themselves!

this week's mystery is the rough start. it only happens in the morning, after the car has been sitting for a time. all lights come on (glow plugs, seat belt etc) at warm up and then it chugs and chugs for 10-15 sec before starting. it does not do this for the rest of the day after I have driven it, and even when I'm at work, when I start it again to leave, no problem. even after a short trip, it will start without a problem.

I thought it might be a slow drain on the battery, but last night I disconnected the battery and still this morning, rough start. the alternator has new brushes and seems fine. battery has water in it.

so now what? could it be the glow plugs? the light still comes on, but I don't know if they've been changed recently. vacuum system? fuel injection? (please God, not that!) it does have new fuel filters and if it was a sludge issue, I would think it would happen all the time. any suggestions are appreciated. I do have a multi meter, but I'm not sure how to set it up to read anything, my dad mostly took care of voltage/electrical testing.
tia
 

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[sounds very much like bad glow plugs!! you also need special tool to ream out the hole when replacing them!
 

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If the Fuel Supply/Lift Pump is not holding overnight fuel can migrate back to the Fuel Tank causing it to sort of loose prime. A small Air leak in the hoses can cause the same thing.
If you have the old style hand primer with the shiny aluminum body and the hard plastic know you need to push it down all the way and turn it and snug it down.

Back to the hand primer. After it has sat all night instead of trying to start unscrew the hand primer (if you have the newer style that is rubber coated you just push down on it and let the spring bring it back up no screwing or unscrewing needed) and start pumping a lot on the hand primer. If you start OK like that the fuel migrating back to the fuel tank is likely the issue.
If you still have that old style hand primer and you pump and it leaks you need a new hand primer and the hand primer can become a source of air leaks.

If the Fuel Supply/Lift Pump needs to be rebuilt (there is generic kids for around $20, the real borsch kits cost more).
If dedide on a kit be sure to get a kit with the little 5mm O-ring shown in post 6.

Rebuild those lift pumps! OM616 OM617 - PeachParts Mercedes-Benz Forum
 
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