cminzey

A friend of mine has a 03 cummins ram 160k miles and we live in MI, Now that it's been real cold when the truck starts it really runs rough until it warms, they don't plug it in but if it's above 50 deg it's starts and runs fine any ideas what this could be ?

Hummin Cummins

Well...

...at about 50 degrees and below is when the engine generally starts on the grid heater

Is he waiting to start the truck until the yellow illuminated pig tail light in the dash turns off

Under 30 degrees I generally cycle the grid heater 3 times (wait 10-15 seconds between the yellow pig tail going out and turning on key); after 3rd time the pig tail light in dash goes out I kick in the starter.

Some times the grid heater relay goes bad. Mine never has. But generally it cycles with a click for the first few minutes after startup. It will dim the headlights as the grid heater cycles on off. Volt gauge will read about 12v at start, 13.5v during grid cycling, 14.8v after grid cycling stops on normal operation.

Also check fuel quality and oil viscosity. Makes a difference in cold temps.

Finally confirm the 03(/early 04) engine control module (ECM) has the most recent flash for 'low power'; it fixes a number 6 injector supply timing issues which causes a very rough idle. My rough idle problem occurred around the same mileage and it was this software issue. My truck is bone stock (except exhaust) so the DC flash worked wonders.

FMB

Hopefully it's his batteries going south for the winter. Have them load tested and replace as a pair if necessary. If the batteries are good, it is about time to check the injectors. How much of a mechanic is he?

cdennyb

I'd make sure the grid heaters are working. If you don't see any voltage drop, and you know the terminals at the grids are getting power, pull the intake horn off and look at them close, sometimes vibration can fatigue the ends where they bolt thru to the battery power cables and that creates an "open" and they never heat up. Just a thought to think about.
I'm with the Hummin Cummins on his thoughts.

soulezoo

This sounds exactly like grid heater problem. Those of us that have done the grid delete *ahem* experience those symtoms as a matter of routine.

Especially these last few mornings in the 20's it's been a bear to start.

1-2-3

i would check all battery termini connections and the other ends of those cable too. A bad connection is free and easy to fix and have a big impact when alot of juice is needed.