# Engine knocks loudly when starting/stopping

**URL:** <https://community.cartalk.com/t/engine-knocks-loudly-when-starting-stopping/63460>\
**Category:** Maintenance/Repairs\
**Tags:** ford\
**Created:** [April 7, 2011, 8:37pm UTC](https://community.cartalk.com/t/engine-knocks-loudly-when-starting-stopping/63460 "2011-04-07T20:37:04Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![dudevideo](https://avatars.discourse-cdn.com/v4/letter/d/f6c823/32.png) [@dudevideo](https://community.cartalk.com/u/dudevideo)\
**Post date:** [April 7, 2011, 8:37pm UTC](https://community.cartalk.com/t/engine-knocks-loudly-when-starting-stopping/63460/1 "2011-04-07T20:37:04Z")

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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!

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**Author:** ![VDCdriver](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/vdcdriver/32/30_2.png) [@VDCdriver](https://community.cartalk.com/u/VDCdriver)\
**Post date:** [April 7, 2011, 8:47pm UTC](https://community.cartalk.com/t/engine-knocks-loudly-when-starting-stopping/63460/2 "2011-04-07T20:47:35Z")

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Has anyone checked the motor mounts?

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**Author:** ![kizwiki](https://avatars.discourse-cdn.com/v4/letter/k/7cd45c/32.png) [@kizwiki](https://community.cartalk.com/u/kizwiki)\
**Post date:** [April 8, 2011, 5:02am UTC](https://community.cartalk.com/t/engine-knocks-loudly-when-starting-stopping/63460/3 "2011-04-08T05:02:01Z")

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It’s a timing problem.

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**Author:** ![ok4450](https://avatars.discourse-cdn.com/v4/letter/o/e9bcb4/32.png) [@ok4450](https://community.cartalk.com/u/ok4450)\
**Post date:** [April 8, 2011, 5:57am UTC](https://community.cartalk.com/t/engine-knocks-loudly-when-starting-stopping/63460/4 "2011-04-08T05:57:57Z")

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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.