1999 E300 Rough Cold Start
 

Well, my 1999 E300 has 90583 miles on it. It is parked in a garage, but lately when you start the engine when it is cold it runs rough for a few seconds and blows some smoke out the back in the process. After a few seconds it is fine and starting it when the engine is warm is no problem. I have no check engine light or glow plug light, but I wonder if there is a weak glow plug. On on had I hope that it something as simple as that, but on the other hand I changed the glow plugs less than three years ago at about 52000 miles. Could this be anything else?

I have never had a glow plug fail without any other electronic reminders on the dash. However, your symptoms are exactly those of one or two bad plugs. I would pull the plug at the relay and check the resistance of each glow plug to ground. Jim

Glow plugs.......replace them. A $700.00 job @ your friendly MB dealer.

Glow plugs HAVE been known to go bad without giving the user any indication other than rough cold starts...it's 99% sure to be one or two bad ones causing your problem since your rough starts are accompanied by smoke.

If you DIY it I'd say test them with an ohm meter, determine which plug(s) is(are) bad and replace only those and not risk breaking one off that is still good.

Could be the clear plastic fuel lines leaking. If air is building up in the system overnight it could start poorly.

I have had that happen so I also checked for it, but not sign of any air in the fuel lines. Also to perhaps clarify is that the engine starts right up, but it is rough for 10-20 seconds.

I have changed the glow plugs before. What would torque me off is that these glow plugs are less than three years old.

Age is not what "wears them out" but the frequency of use. Your car is very low miles so I would assume you don't use it too much so I would think you got a bad one from the factory. Did you use OE plugs or aftermarket when you did yours? Test them with an ohm meter...I'd bet you'll find one is out. If you are lucky it is the front one which you can get to without pulling the IM off.

Look at the bright side. Even if you locate a bad plug they were all out three years ago so hopefully it will spin out now. At least make sure to put anti seize compound on the threads of the replacement.
.Age or milage alone does not define the life of a glow plug. Just like light bulbs one can fail earlier than the average.

I do not know the OE from aftermarket glow plugs. I installed Bosch glow plugs. I see that there is another supplier named Beru. I do not know if one is 'better' than the other.

OE means you bought them from the dealer...anything else would be aftermarket, though they could be identical (OEM) to that which the dealer sells. Frankly I'm not sure if MB uses Bosch or Beru as their supplier for the OM606 engines...but if you used Bosch they should give you a decent life. Sometimes, not reaming out the carbon from the chamber has been known to cause shortened plug life...did you clean out the chambers with the proper reamer before installing the new plugs?

I've bought two sets of glowplugs for an OM606 from the dealer - and they were all Beru.

One bad glow plug throws the check engine light on my '99. Not sure if the '96 is the same, but I would guess that it is.

The OM plugs on my 99 were Beru's.

Not so on mine........ But it indicates glow plugs, nonetheless..

Is there a thread on how to check the GP resistance on a 606?