Q: Engine shaking and knocking after spark plug replacement.

asked by on December 22, 2015

I had a spark plug and ignition coil burn up. When I went to replace it the spark plug hole threads were stripped. Tapped and rethreaded and waited 24 hours before installing a new ignition coil and 4 new iridium spark plugs. When I started it, the engine was shaking badly and it sounded like something was knocking around inside.

This sounds to me like the cylinder head has been severely damaged. If the burn of the coil and spark plug started on the plug end this would mean that combustion chamber temperatures from inside the engine were allowed past the electrode surface of the spark plug. The explosions from the fuel being ignited inside the engine must have caused the spark plug to burn up. I would first recommend having a qualified engine technician come and do an inspection of your engine. You may have a crack in your cylinder head. As for the knocking sound, a piece of metal from the cylinder head may have broken off during the rethreading process and fallen on to the piston. When the engine was started again the piece of metal must have been getting smashed between the valves and the piston itself. I would not run the engine anymore until the inspection is done to prevent any further damage.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing


Experienced Mechanic?

Earn up to $70/hr

What others are asking

How do I adjust the electronic range select (ERS) system?
The electronic range select (ERS) system limits the highest gear that your vehicle can be using. When in ERS mode, tap the shift lever right, towards the +, to add an extra gear to the ERS. Tap the lever left,...
How does the rear window defroster work?
Your car is equipped with both a front and rear defroster. While the front defrost is tied into your air conditioning system and uses the fan, the rear defrost is different. Here’s what you need to know to work it:...
Car dead
Hi there. A slightly open car door will leave your dome light on causing your battery to drain. If your battery drains completely it will need to be charged by a battery charger. A jump will only work if your...
Vacuum leak
Hi. This is a very common failure on vehicles like yours. So common, in fact, that there is a technical service bulletin (TSB) on it. The TSB is XT303-13 and it addressed the hissing sound from under the hood, as...
Engine rumbles and vibrates while idling
You might want to try watching my video "How to Fix a Car That Idles Poorly (https://www.youtube.com/watch?v=eQpPcdvSBks)." You just take the plastic plenum that goes from the air filter to the intake and get some throttle body cleaner. Spray the...
Check engine light on.
The testing you did using the CIL may not have been done correctly. During these tests you will need to cycle the clutch and accelerate the engine when the separator codes were received. This is done with a superstar 2...
Ac compressor fuse blows 2004 Ford Taurus
Hi there - from your symptoms, it sounds like your AC compressor clutch (https://www.yourmechanic.com/question/i-want-to-replace-my-ac-compressor-clutch-by-eric-r) has locked up, or the clutch bearing has seized, such that the serpentine belt tries to turn the compressor whenever you start the engine. (REALLY problematic...
I have a 2013 Acura Ilx. When I push button on handle on drivers side it no longer beeps and locks.
Hello. This is a programming issue within the door locking system. The programming can become corrupted and cause this. You will need to take the vehicle to the dealer in order to get it reprogrammed.

Related articles

How Does a Distributor Work?
In In older cars, a distributor is one of the central parts of the ignition system. Since the early 1990's, many automakers have moved to using ignition systems without distributors. Though the number of cars with distributors has declined over...
Symptoms of a Bad or Failing Ball Joint (Front)
Common signs include clunking noises and excessive vibration from the front, and you may start steering to the right or left unintentionally.
How to Read Your Spark Plugs
Car spark plugs create the spark necessary in the combustion cycle. Check your spark plugs to improve your engine efficiency and performance.