Hello Benz Friends,

I've owned my N/A 87' 300D for 5 years now. I've never had this problem. I've done a considerable amount of work on it, and am well versed in its history. This February, here in Alberta we had a really bad cold snap, and the 10 year old Group 49 battery died. I went to start the car after a few days of -40C weather, and even plugged in, it wouldn't go. It would chug, and then run out of juice. After charging it, same effect. I bought a brand new battery, hooked it up, used a big fast charge start aid, and struggled through 4 minutes of on/off cranking and eventually it fired up. After it started and warmed up a bit, it drove like a dream. For some reason after this point, it's been ruthlessly hard to start. If I don't plug it in, even in minor cold temps like +5C, it struggles for 45 seconds to start until it starts winding faster, and then fires altogether. This was never a problem, even in -20, it used to fire on the first crank.

When the car is warm, it starts really easily. I've replaced all the fuel return lines, replaced the fuel filter and pre-filter, there's no fuel leaks from the little pre-heater on the engine. All of the injectors were overhauled 2 years ago in may with new Monarch nozzles. All pretty much breaking within 50 psi of the 1668 psi recommended for the N/A OM603.912 engine. I know then engine is getting fuel, there's lots of exhaust smoke when it's trying to fire. Glow plugs were my thought. I replaced them all 3 years ago with Monarch glow plugs, reamed the ports, the whole shebang. I checked voltage at each of the plugs at its at about 11.3 - 11.6 volts. I'm not as good with electrics as I am with mechanics. The plugs light on the dash is working normally. It seems the relay too is working normally, I can hear it click on and off.

Does anyone have any ideas as to what to do?

Would be a great help. Thanks

 

Rough start:
Check to see if you have any signs of moisture inside your cap.
There is a large o-ring around the orange-looking insulator behind the rotor mount. Check it's condition.
The o-ring prevents moisture from getting into the distributor.

 

It's a diesel, and shouldn't have a distributor.

 

Have you checked the how much resistance there is on the glow plugs? You can measure it a multimeter by connecting one probe to a earth and the other probe on the glow plug. When they go bad they usually have no circuit or no resistance.

 

@W124Herman
Check that your idle control solenoid is functioning correctly?

 

Hi Habil,

Thanks to you, i figured it out. I didn't think to test the resistance of the plugs at first, just the voltage to each plug which seemed fine. 4 of the 6 plugs were blown. Thanks for your tip. It saved my bacon. I didn't think it could have been the plugs because I just replaced them and did the whole reaming service 3 years ago. But i guess things happen. Thanks again.

 

That's good.
Monark glow plugs seem to have a bad rep. I've got French made Bosch plugs, and they have lasted about 7 years so far. Beru are also suggested.