when i'm going downhill usually in 3rd gear my 97 cummins likes to blow white smoke anyone know the cause of this? only does it when cold or going downhill

 

Sounds like a faulty injector.

 

was the truck recently overhauled?

 

mine does the same thing when you cold start it and you rev it a lil... idk why

 

mine does it when you really get in to it in park or neutral then it clears out no clue why?

 

once i hit 4th gear and get on it it stops...i have no clue.

 

a combination between 370 marine injectors, marine head gasket, new engine and style of pistons is why mine does it

 

might have some one check the timing of ur pump. mine smoked like a low compression diesel at idle. mine was set at 11 degrees. bumped it up to around 16 degrees, starts and idles alot better, hardly any white smoke. just a sugesstion on a possibility.

 

Valve stem seals also cause smoke a idle.

 

How about air getting in the fuel system somewhere?.Its a known cause for white smoke on all 12v trucks.Not saying its what your experiencing but I would certainly look the fuel system over for bad lines.