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HomeTips & GuidesEngine Cranks But Won’t Start: Find The Reasons

Engine Cranks But Won’t Start: Find The Reasons

About Engine Cranks But Won’t Start, In a single lifetime, your car is bound to suffer several problems. Most of the problems are associated with electric circuits and the engine. 

You’ll hear a cranking sound when you turn on your car before the engine starts. However, if you hear a cranking sound, but the engine fails to start, your battery is fine, and the problem will likely be with the engine.

The article below discusses why the engine cranks but won’t start.

Table of Contents

The Principle Behind Any Reciprocating Internal Combustion Engine

Most people would define a car as a machine you fill with gas to move you from one point to another. However, have you ever thought of how exactly it works? 

Internal combustion engine understanding

Unless you already moved to an electric vehicle, you’ll be pleased to know it all happens thanks to the internal combustion engine. 

If you ignite a small amount of fuel in an enclosed space, it’ll release much energy as expanding gas

If one can make a cycle allowing themselves to continuously set off such an explosion and find a way to harness the energy, you have an engine’s core.

Most cars with gasoline engines use a four-stroke cycle to change gasoline to motion.

Four strokes

  • Exhaust stroke
  • Combustion stroke
  • Intake stroke
  • Compression stroke

A piston connects to your crankshaft via a connecting rod. Therefore, when your crankshaft is revolving, it resets the cannon. 

Follow the steps regarding what happens when the engine goes through a cycle.

  1. The piston begins above opening an intake valve. Then, the piston closes, allowing the engine to take in gasoline and air. Remember that only a drop of gas must mix with air to work.
  2. Now, the piston goes back to compress the air/fuel mixture. Compression helps the explosion become more powerful.
  3. Once the piston reaches the top, your spark plug sparks, igniting the gas. Inside the cylinder, the gas charge explodes and drives down the piston.
  4. Lastly, the piston strikes its stroke at the bottom, opening your exhaust valve. The exhaust then exits the cylinder and moves to the exit through the tailpipe.

After the process, the engine is ready for another cycle. Therefore, it takes in another charge of gas and air. Inside the engine, the crankshaft converts the piston’s linear and rotational motions. The rotational motion is a plus since it plans on rotating the vehicle wheels anyway. 

Car engine mechanics concept

Car engine mechanics concept

Basic Engine Parts

Now, let’s discuss the various parts of the engine that band up to make it all possible.


The cylinder is your engine’s core, with the piston shifting up and down inside. Single-cylinder engines are generally lawnmowers, as cars typically have eight, six, or four cylinders.

In a multi-cylinder engine, the arrangement of the cylinders is flat (boxer or horizontally opposed) or V.

Different setups have various merits and demerits regarding manufacturing cost, shape characteristics, and smoothness. These merits and demerits make them ideal for specific vehicles.

Spark Plug

A spark plug creates the spark, igniting the fuel/air mixture to allow combustion. The spark has to ignite at the right time to work properly.


The exhaust and intake valves open perfectly to allow fuel and air inside to allow the exhaust to exit. Remember that both valves close as combustion occurs to keep the chamber sealed.


The piston is a metal cylindrical piece moving up and down in the cylinder.

Piston rings seal your cylinder’s inner edge and the piston’s outer edge. The ring has two functions;

  • To prevent the exhaust and combustion chamber’s air/fuel mixture from leaking to the sump as combustion and compression occur.
  • To prevent oil inside the sump from leaking into the combustion area, where it would burn and go to waste.

If your car burns oil and you must add a quart every thousand miles, it’s because your engine is aged and your piston rings don’t properly seal everything. Luckily, most modern cars use more durable materials for the piston rings, so modern engines are more durable and go longer without needing an oil change.


Caption: Piston

Connecting Rod

A connecting rod attaches the crankshaft and piston. It can rotate on either end to ensure the angle can adjust as the crankshaft rotates and the piston moves.


The crankshaft aims to turn the piston’s up-and-down motion into a circuit motion.


A sump surrounds your crankshaft. It has some oil that collects at the oil pan’s (sump) bottom.

Troubleshooting the problem when engine cranks but won’t start

Since you now understand how your engine functions, you can now comprehend the small components that can prevent it from functioning.

Bad Fuel Mixtures Can Happen in Different Ways:

  • You’re out of fuel; therefore, your engine only gets air and no fuel.
  • With a clog in your air intake, your engine gets fuel but insufficient air.
  • Your fuel system could supply minimal or excessive fuel, causing improper combustion.
  • An impurity in the fuel (water in the tank) could hinder combustion from occurring.

Lack of Compression

If your fuel and air charge isn’t properly compressed, combustion won’t occur as expected. That could be as a result of the following reasons.

  • The exhaust and intake valves aren’t properly sealing, allowing a leak as combustion occurs.
  • Worn-out piston rings that allow the fuel/air mixture to leak as compression occurs.
  • A hole in the cylinder.

Commonly, holes in the cylinder occur where the cylinder head attaches to your cylinder.

Normally, the cylinder head and cylinder attach with a slim gasket pressed between the two to ensure they seal properly.

If your gasket wears out, small holes form between the cylinder head and cylinder, causing leaks. 

Lack of Spark:

A spark could be weak or nonexistent due to several reasons.

  • The spark might be weak if the spark wire or plug is old.
  • If the spark wire is missing or cut.
  • If the system sending the spark to the wire isn’t functioning.
  • If the spark happens too late or too early during the cycle, the fuel fails to ignite at the right moment.

Many Different Things Could Go Wrong.

  • If the bearings allowing the crankshaft to turn freely are old, it can’t turn, and therefore the engine can’t start.
  • If the valves don’t close and open at the right moment or are completely nonfunctional, neither air nor exhaust enters and exits as expected, causing the engine to fail.
  • If the oil runs out, the piston can’t freely move inside the cylinder, causing the engine to seize.
Mechanic Changing Engine Oil

Caption: Mechanic Changing Engine Oil


All the above components should be fully functional for your engine to run properly. However, if your car doesn’t even crank, there may be a battery failure.

The battery makes 12-volt power available to everything in the car needing electricity, including the ignition system, through the vehicle’s wiring. Need help with wiring harnesses, contact Cloom.

Hi I am Christa, sales manager of Cloom.

I have extensive expertise and experience in wiring harnesses and I believe I can help you.

And we have a very professional technical team who can clearly understand the customer’s needs and give professional suggestions and solutions after receiving the drawings.

If you also have wiring harness needs, please send me the drawing so that we can give you our quote and start our business.

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