Car Won’t Start After Spark Plug Change ( Why & How To Fix)

The reason your car is not starting after a spark plug change is because of a number of reasons.

The most common and likely is that you have not installed the new spark plugs correctly.

If the mounting process was wrong, it becomes hard to get the car to fire on all the cylinders. 

So, the best thing to do is to diagnose and find where you made the mistake and have it corrected before the car can start once more. 

Potential mistakes while removing the old spark plugs

Several things might happen when removing the old spark plugs. This would definitely lead to a problem while trying to start the car later. Here are a few ideas to keep in mind. 

  • Sometimes the old spark plugs might have jammed into the cylinder. If you end up using a lot of force to remove the spark plugs, you might end up damaging the input’s torque spirals. This means the new sparkplugs would not fit as well. 
  • Having bad ignition in your car leads to carbon build-up on the plugs. So you have to clean the inputs first before installing the new plugs or else they would get covered in carbon or oil and still not start. 
  • You may have forgotten to disconnect the coil connectors first. This is key in ensuring you do not damage some of the wires and vital in ensuring a proper supply of power to the spark plugs. 
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Here is a video on how to remove spark plugs

YouTube video

Potential mistakes while installing the new spark plugs

It is still possible that at times you make mistakes while installing the new spark plugs. It could be that you are new to this. Not to worry as we discuss some of the potential mistakes you might do so that you can avoid them. 

  • If the spark plugs are loosely fitted, then it would be hard for them to ignite, thus the reason the car won’t start. You are supposed to use the right socket or torque wrench to tighten the spark plugs correctly. 
  • Sometimes the problem can be with the way you have reconnected the coils. Remember that each connector has a specific coil to be attached to. If you reconnect incorrectly, then the ignition system route might be incomplete or short-circuited. 
  • Forceful installation sometimes breaks the firing pins or the plug’s ceramic coating. Here now you have a broken spark plug already that would not do the job. 
  • Some novice DIYers often install the wrong spark plug for the engine type. For this issue, the engine might fire, but sometimes it might not. Or, even if it runs, it will be rough. Check your engine type and only use the correct spark plugs for that engine. 

Here are tips to know when it is time to replace the spark plugs

YouTube video


What are the other reasons the car won’t start?

It could be that you have a dead starter, a low or dead battery, the timing belt broken or skipped, no spark coming from the ignition coil, and a bad fuel pump. 

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Should you reset the ECU once you change spark plugs?

It might not be necessary. Changing spark plugs has nothing to do with the ECU. Just ensure the plugs are installed correctly and you should be fine. 

Will new spark plugs lead to a rough idle?

It is highly unlikely but yes, they can cause rough idle. This is mostly if you use the wrong spark plugs for the engine. 

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