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Irregular engine knock when started

Tiny
TOMBOIBOOGALOO
  • MEMBER
  • 1999 MERCURY MARQUIS
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 83,000 MILES
The engine is knocking when the car starts. The knocking quickens until about 30 or 40 mph then disappears. I'm thinking it could by the knock sensor or the rocker arms and/or push rods, but I'm at a loss. Any help would be greatly appreciated.
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Saturday, October 5th, 2019 AT 4:40 PM

1 Reply

Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

An engine knock is usually associated with connecting rod or main bearings that have started to fail and the knock is caused by the slop of the connecting rod rotating around the crankshaft or the crankshaft around the main bearings. This is the same engine I have in my vehicle, so I know it pretty well. It is an overhead cam design and does not employ push rods, and the valve lash is self adjusting, so if a knock is present it is going to be in the rotating assembly, and probably failed connecting rod, crankshaft. connecting rod bearings. The only way to know for sure is to disassemble the engine and fix the damage. Here is a link for you to go to below that explains it more in detail:

https://www.2carpros.com/articles/engine-noises

Please go through the guide at the link above and report back with how you want to proceed, please. We can offer step by step directions for any problem you would like fix on your vehicle.

Thanks,
Alex
2CarPros
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Saturday, October 5th, 2019 AT 5:10 PM

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