I have some XP with EMD engine,though it was a V20.
White smoke in outlet is unburned fuel.A sencitive component on this engine is the turbine clutch.
At low load, the turbine is coupled to the crank shaft using a clutch, which at high load (enough exhaust gas pressure to drive the turbine)will unclutch.
If this clutch fails to engage, you will have a very rich combustion (not enough air)on low load operation.