Some symptoms of a problematic 6.7 liter Powerstroke diesel engine include stalling, overheating and engine failure. Stalling usually relates to issues in regards to air leaks, while overheating and engine failure usually occur at the same time.
An air leak is often referred to as a vacuum leak. These occur when hoses, which are used to seal the airflow from one end of an engine to another, are broken. The air seeps out and causes an engine to stall.
Overheating results in the engine blowing its head gasket. The head gasket seals the head with the block. Blowing it can also result in the engine failing completing, requiring a complete rebuild, in order to be repaired.