What causes firecracker smell and missing and shaking?

Hello, The Pacifica is not known for reliability in the least bit, and engine oil leaks under the hood are quite common. Look at the exhaust manifolds, as one of them is likely covered in oil from a leaky valve cover gasket. This is very common, and a valve cover gasket leak is also a vacuum leak, so the vehicle will not perform as intended. Let me know what you do/don't find, and if there is a sizzling sound when the vehicle is shut down after a normal drive. You will likely see smoke coming from the sizzle sound location.