If you have a 5.4 Triton engine, there are several places where the vacuum can leak. One of the most common places is at the intake manifold gasket. This gasket can develop leaks over time and cause the engine to lose power and run rough. Another place that vacuum leaks can occur is at the PCV valve. This valve is responsible for recirculating exhaust gases back into the engine, and if it's not functioning properly, it can cause a vacuum leak. Finally, vacuum leaks can also occur in the hoses that connect to various components in the engine bay. These hoses can become cracked or damaged over time, which will cause a loss of pressure and result in a vacuum leak.