Why does my 2007 Crown Victoria Police Interceptor vibrate when I get to 40 miles an hour and then die off back to normal by the time it reaches 50

a ha moment interceptor uses the highest out put available if not custom

did u check ur passin gear cable

check for bad ground open circuit

Notorious for intake leaks, the composite plastic intakes crack and leak coolant-as to the lack of power, you mght have overheated it and done some damage to the engine. There was a recall (information below) for the 4.6 for the intake-the overheating and lack of power means you should at least have compression checked and go from there-you may have bad head gaskets or worse. Do a compression test before you do anything else.

Ford Motor Company will extend the recall (01M02) on 4.6L V8 equipped vehicles with plastic intake manifolds. Some of the composite intake manifolds used on 4.6L SOHC engines may develop fatigue cracks at the coolant crossover duct. This condition could result in engine coolant leakage which, if not serviced, may cause engine overheating. Complete loss of coolant may result in engine damage or engine failure.
The updated recall now includes:
• Certain 1996 through 2001 Model Year Crown Victoria Police Interceptor
• Certain 1998 through 2001 Model Year Crown Victoria with Taxi
• Certain 1998 through 2001 Lincoln Town Car Limousine and Livery Prep Package
• Certain 1996-2001 Crown Victoria Taxis, Police cars and Lincoln Town Car Limousine and Livery cars.
• Certain 1996 through 1997 Crown Victoria Police Interceptor Vehicles with 4.6L SOHC engines built at the St. Thomas Assembly Plant from the beginning of production for the 1996 Model Year through January 28, 1997.
• Certain 1998 through 2001 Crown Victoria Police Interceptor Vehicles with 4.6L SOHC engines built at the St. Thomas Assembly Plant from November 22, 1997 through December 15, 2000.
• Certain 1998 through 2001 Crown Victoria Taxi Vehicles with 4.6L SOHC engines built at the St. Thomas Assembly Plant from November 22, 1997 through December 15, 2000.
• Certain 1998 through 2001 Lincoln Town Car Limousine Prep Package and Livery Vehicles with 4.6L SOHC engines built at the Wixom Assembly Plant from November 22, 1997 through December 15, 2000.

which fuse?

I would try to replace your spark plugs, and spark plug wires, My 88 Vic did the same thing...now it runs like a champ....you could also try fuel injector cleaner.

get it scanned before doing anything else

Depends on whether or not you are going with Brand new or are Going to Machine the Old ones. Which way you goin????

it is DOHC

Have you checked the fuel filter. Fuel pump will pressure up, but fuel filter could be clogged and not work without the pressure of the fuel pump.