Engine knocks loudly when starting/stopping

ford

#1

I have a 2002 Crown Victoria LX. The engine runs great with the exception of a loud knocking sound sometimes when starting or stopping the engine.



When starting, it’s a single loud knock after the engine turns over. When stopping, it’s anywhere from one to several as the engine motion comes to a stop. When it’s several (probably 4 or 5) they are quick but it’s apparent that the rate slows down slightly over time, as if it’s a moving part inside the engine coming to a stop.



It is worth noting that about one-third of the time when turning the car on or off, there is no noticeable knocking sound whatsoever. Maybe something is loose inside?



Thanks for any suggestions!


#2

Has anyone checked the motor mounts?


#3

It’s a timing problem.


#4

Some car parts stores will scan the car for free and this should be your first step.
It’s possible that you’re hearing a severe spark knock on startup and dieseling during shut-off.

This could be caused by an ECM controlled fault with the ignition timing, heavily carboned up engine top end, oil consumption problem, or possibly a MAF sensor fault/air leak.

This car should run fine on 87 octane but if 87 is being used in conjunction with a known problem (oil use for instance) it’s possible the gasoline could be contributing to this.