Thanks to everybody for this great thread, and the cutaway views. Where did you get those? They are not in the 3.2 workshop manuals that I have.
Here is what I have gathered after reading the thread, and working with my tensioners:
Failure Modes
Clogged restrictor orifices. The restrictor orifices are pretty small, so they could get clogged by debris from some sort of post-filter internal situation. This would prevent oil from getting into either the supply chamber or the piston chamber, or both even. The result would be a collapsed tensioner.
Broken main spring. If the main spring is broken, the piston can collapse when the engine is shut down. On startup, it will take a longer time to pump up, or it may never pump up.
Internal check valve stuck open. - The tensioner will not pump up. This will exhibit the symptoms of a collapsed tensioner.
External check valve stuck open. - The supply chamber will not pressurize. This will exhibit the symptoms of a collapsed tensioner.
Engine operating modes:
Brand new engine or brand new tensioners. - Engine oil pressure fills up the supply chamber. The external check valve vents out the air as it fills. The supply chamber inlet orifice is sized so that, once it is filled with oil, the oil pressure is not great enough to pop open the external check valve, so it closes. Oil flows into the piston chamber, past the internal check valve. Air is forced out the spiral leakdown passage. Once the piston chamber is full of oil, the pressure from the chain presses on the piston and closes the internal check valve. The tensioner is now ready for normal operation.
Normal operation. - As the engine warms up, the spacing between the cams increases. If the tensioner did not have some leakdown, the tension would become too tight. As the chain pushed harder on the plunger, oil is forced out the spiral groove. The spiral groove acts as an orifice. Once the force on the chain is in equilibrium with the rate of oil loss through the spiral groove, the normal operating condition is achieved. The internal check valve and the cylinder orifice work together with the spiral groove to set the operating tension just right.
Shutting down. - The oil supply pressure dwindles down to zero, but the supply chamber should still be full. The chain is still pressing down on the plunger, so oil will still leak out of the spiral groove. This lets the plunger collapse a small amount, until equilibrium is reestablished.
Subsequent starts. - The system stays filled with oil. If the engine has cooled down completely, the chain will be a little slack again, but the plunger spring will keep things tight until engine oil pressure refills the tiny amount of oil lost at shutdown.
Other notes. - I would say pressurizing the tensioner with air is not a good idea. The orifices are not sized for air, so you could get too much force on the internal check valve, and maybe blow it loose. I think priming it with oil, even just partially, is a good idea, but not mandatory. It shaves a few seconds off the time to achieve tension. The tensioner and its internal spring do not quickly adjust tension. It is a gradual thing done only to compensate for the expansion of the engine. The damping of dynamic motion of the chain is handled by the ramps.
