I hope thos acceptable in this forum.

Recently purchased DP. Has Cummins M-11 400 hp, 25000 mi on it.

Today the first morn that I had started it when temp was about 45 degrees.

It started OK, but the idle was unsteady, pulsing probably 600-900 rpm about one cycle per second. idle was steady after driving off and warming a little.

Do not know what behaviour a diesel might have when starting as the weather gets cooler. Is this symptom terribly abnormal? If so, what is a likely cause?

Thanks for any comments/advice/hints

 

I've heard many diesels do this when started cold. I think it's because they aren't hitting on all six every time around and the governor is adding fuel to compensate for the RPM drop from the misfires, then cutting fuel when RPM goes up, causing misfires. This cycle repeats until the combustion chambers get hot enough to light the fire every time. Engines I've heard do this: IH DT408 and DT466, Cummins 6BTA (not in a Dodge) and 6CTA. I don't think it's uncommon.

BTW, welcome to DTR.

 

It might have a small air leak in the fuel system but probably is just cold and "hunting". There may be an adjustment screw on the governor that stops the rack from going down past idle. It's probably an easy adjustment but won't hurt to leave it alone. It's just talkin to ya. You woke it up early and want to put it to work.
John

 

i'd agree with wannadiesel. my truck does it too, especially with the marine pump on it (still did it for a couple seconds with the stock pump on a cold day but cleared up quick).

Tom

 

There is no adjustment for idle hunting on this electronic engine. At least not that is accessible to us in the field. Your engine should have a steady idle down to 32F or below. If it doesn't, a few places to look are: air in the fuel, plugged fuel filter, or a failing engine position sensor. Hope that helps, and PM me if you need more assistance.