I have had white smoke on startup for some time but it normally dissapeared after a few minutes when the engine warmed. The problem is now eratic and appears to be tied to the electrical device that is mounted directly above the injector pump output ports. I would like to know what this device is, and also if there are any tests associated with it.

 

That's the shutoff solenoid, it has nothing to do with white smoke. The piece you want is the KSB solenoid, it's on the side of the pump.

Is your truck intercooled or non-intercooled?

 

Thanks for the info.
The truck is an intercooled '91 W350 - everything is standard on it.

 

OK, you should have voltage to the KSB solenoid on the side of the pump when the engine is cold (intake manifold temp under 90 degrees). If you don't, check the switch on top of the manifold (it's the one towards the back). That switch gets power from the shutoff solenoid.

 

It seems there were two problems - a loose/faulty terminal on the shutoff solenoid and a faulty temperature switch. The terminal was easy to fix. The temp switch was confirmed by shorting out the plug (switch opened after about 1 min with an ambient temp of about 50F).

 

Glad I could help.