The cold advance switch on the back end of the right cylinder head by the #8 injector can cause excessive smoke if it's bad. Below about 90 degrees it's normally closed and tells the injector pump to squirt extra fuel into the engine. This can cause excessive smoke for a few minutes until the engine begins to warm up. These switches have a bad habit of breaking but are pretty easy to replace. It lives in the engines water jacket so have your new switch ready to jam in the hole when you take out the old one. That way you won't lose too much coolant.
From the HMMWV Diagnostics Guide:
4. Housing Pressure Cold Advance System:
This system consists of a housing pressure
cold advance solenoid (23), a housing
pressure regulator (22), and a housing
pressure cold advance switch mounted on
the rear of the right head assembly.
When the engine is cold, (below 90°F), the
housing pressure cold advance switch is
closed. With the switch closed, current flows
across the switch to the housing pressure
cold advance solenoid (23), activating and
opening the housing pressure regulator
valve (22).
The HPCA solenoid (23) is activated through
a temperature switch located at the rear of
the right cylinder head assembly. The HPCA
solenoid is located in the governor housing
cover. For cold starts ,when engine coolant
temperature is low , (below 90°F), the solenoid
plunger lifts the check ball off its seat. This
reduces housing pressure to almost zero.
With no housing pressure in the advance
mechanism (20), the fuel at transfer
pressure can advance the cam ring (21),
more easily when the engine is cranking.
Injection timing is advanced about 3° to
reduce white smoke and improve cold-idle
smoothness. Now that the engine is warmed
up, it will run smoothly. The switch operates
similar to an automatic choke on
automobiles.
