Driving with Missing Spark Plug – Is it Possible?

Can I drive my car with a missing spark plug?

Yes, theoretically a car could run with one or even two missing spark plugs. Would the vehicle run with fewer than two missing spark plugs? I would say, not a chance.

Even though the engine could run without a spark plug, that does not mean you should! Here’s why

An engine needs 3 important things to run.

  • Air
  • Fuel
  • Spark

Spark plugs ignite the fuel that is sprayed into your cylinder. Without a spark, fuel will dump into the cylinder.

If the spark plug is removed from the vehicle the fuel will likely be shot out of the block. If the spark plug is still in the block, the fuel will instead leak past the piston rings and into your oil pan. In either case, it is important your spark plug should be replaced as soon as possible.

Will a missing spark plug damage an engine?

If left untreated long enough, a faulty, broken, or missing spark plug will cause damage to your engine.

Missing spark plug:

Engines require compression to run efficiently, with a missing spark plug the engine will have a major loss of compression. The engine will run rough, oil can cover the engine bay, and fuel can leak into the oil pan. All of which can be unsafe and damage the vehicle.

Broken spark plug:

In extremely rare cases, the spark plug can break inside the cylinder. If this is not addressed immediately the chunks of metal from the spark plug will damage the cylinder wall, piston, valves, and piston rings; All extremely expensive repairs.

Faulty spark plug:

A faulty spark plug will not effectively ignite fuel. When fuel does not ignite completely, it will drain past the piston rings and into your oil pan. The fuel inside an oil pan will mix with engine oil.

While both the engine oil and fuel are oil-based, each is completely different. fuel alongside oil does not play nice, fuel will begin breaking down oil on the molecular level.

If left untread, the engine oil will lose all lubricating properties, allowing engine parts to wear at an accelerated rate. Often causing major engine damage!

How much do spark plugs cost?

Depending on the vehicle, spark plugs prices range from $3-$20 each. A small price to pay for a well-running vehicle.

how much does it cost to replace spark plugs?

Replacing spark plugs can be quite easy with most vehicles, I suggest learning how to replace them at home. If you need to buy tools the repair can cost about $60-$300 depending on the vehicle.

If the vehicle you drive has spark plugs that are much harder to replace, you may need to bring the vehicle to a mechanic. The repair bill will range between $200-$600 depending on the car and where you take it.

Faulty spark plug symptoms:

A faulty spark plug can be identified easily with the right know-how. You could simply bring the vehicle to an auto parts store so they can look at the current engine repair codes the ECM is triggering. You could also see if your vehicle has these symptoms:

  • Engine code
  • Rough idle
  • Sluggish acceleration
  • Backfires
  • Hardstarts

How can I test a vehicle’s spark plugs?

Engine code:

The easiest way to test for a faulty spark plug is a scan tool. Your local auto parts store may have one for rent, or they will test the engine codes for you. The next best thing is to buy a scan tool.

Some are extremely expensive, but for our purposes, a cheap scan tool will get the job done now. It will also help with future diagnosis later!

Spark plug tester:

A spark plug tester like the one in the picture above is an inexpensive method of testing your spark plugs. Make sure to test all spark plugs on the vehicle. It is always best practice to replace all spark plugs if one is malfunctioning.

What should a spark plug look like?

When you remove a spark plug from an engine it is normal to see some brown/black carbon build-up. It is not normal to see extreme amounts of carbon build-up. The spark plug should not be wet or have oil on it.

Why is my spark plug covered in oil?

Oil on the spark plug is likely due to valve seals that are dry rotted or broken. Oil from the engine is squirted on top of the rockers that have pushrods connected to them from the camshaft. If you have oil on your spark plug, the valve is leaking into the cylinder. You may also see white smoke or a burning oil smell.

Why is my spark plug wet?

Your head gasket may be blown, the head has coolant running through it to keep the engine cool. When you have a blown head gasket, the coolant now how the ability to make it into the cylidner. This could cause many issues, like wet spark plugs. Sometimes, it will cause a hydro-locked motor if enough coolant goes into the cylinder.

See this guide for checking head gaskets.

What happens if you unplug a spark plug with the engine running?

Spark to that cylinder will stop, likely throwing an engine code, and running rough. For short periods this will not damage the engine.

How long do spark plugs last?

Spark plugs last anywhere between 20,000-80,000 miles depending on the make, model, and year of the vehicle. It is also recommended to replace spark plugs at certain year intervals. See your vehicle’s manual for the correct milage and intervals.

Does changing spark plug increase performance?

Yes, replacing spark plugs that are underperforming or not functioning at all will increase the performance of an engine. It will likely resolve hard starts, sluggish acceleration, backfires, and rough idle issues. Along with this, you will see a power increase from the vehicle.

Will replacing spark plug wires increase performace?

Not necessarily, If you have a broken spark plug connection or broken spark plug wire, replacing that wire or connection will increase performance. Otherwise, replacing functioning spark plug wires is good for aesthetics or maintenance if they are starting to rot away.

Recent Posts