I have a 2003 F150 5.4L that I bought new. Several years ago it began to randomly experience a serious problem when running between 1600-1900rpm. It happens in all gears and in park, and has never happened at any other rpm range. It seems the computer shuts the engine off and instantaneously turns it back on. The tach drops and immediately pops back up - accompanied by a serious thud that shakes the truck. It first created no code, then for a while gave a "crank sensor" code, and now is again sending no code. I have changed the crank sensor and cam sensor (both Motorcraft), but it has not helped. Ford says they can't find a problem and have never heard of anything similar. Hard to believe with millions of F150s on the road. Anyone have any ideas, suggestions, or solutions? Thanks

 

Working from the effects only take you just so far.
The next step is looking at the issue with a Scanner to see what live data shows.
A crank senor fault code is a pretty good indicator.
The crank sensor is the reference for all that goes on.
My bet is it is vibration sensitive.
Somewhere in the crank sensor cable harness it may be grounding out or an open is occurring.
When the crank sensor signal goes missing everything stops.
At least move the harnesses around to see if the fault returns.
Good luck.

 

I had the Sam issue in my 2004, After reading many posts last year found out it was the VCT
The screens broke and they were stuck and unable to adjust the timing.

I replaced both and it runs as good as new.
in the link below he reviews it, I was able to to it without removing the valve covers with a long extension. You will see in the video below that the screws are locked in. but be careful as the guy in the video says.

 

No VCT in 2003 - that's a 2 valve engine.