A 4-stroke engine turns fuel into rotational motion using four piston strokes per cycle. Almost every gasoline car engine on the road works this way.
Animated: how a 4-Stroke Engine actually works
🔧 How It Works, Step by Step
1
Intake stroke
The piston moves down and the intake valve opens, drawing a mix of air and fuel into the cylinder.
2
Compression stroke
Both valves close and the piston rises, squeezing the air-fuel mixture into a small, dense charge.
3
Power stroke
The spark plug ignites the compressed mixture and the explosion forces the piston down, producing power.
4
Exhaust stroke
The exhaust valve opens and the rising piston pushes spent gases out of the cylinder to start the cycle again.
🧩 The Key Parts
Piston
Slides in the cylinder to compress the mixture and capture the power stroke.
Valves
Open and close to let air-fuel in and exhaust out at the right moments.
Spark plug
Ignites the compressed air-fuel charge to start the power stroke.
Crankshaft
Converts the up-and-down piston motion into rotation that drives the car.
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The 50 most common check engine codes with likely cause and DIY fix cost. Sent once.
🩺 Signs of a Failing 4-Stroke Engine
Rough idle or stalling
Loss of power or poor acceleration
Misfires or hesitation
Poor fuel economy
Excessive exhaust smoke
⚠️ Common Problems
Low compression
Worn rings, valves, or a blown head gasket let cylinder pressure escape and rob the engine of power.
Ignition or fuel issues
Bad spark plugs, coils, or injectors upset the precise timing of combustion and cause misfires.
💰 Cost to Fix
$300-$4,500typical range to repair or replace, parts and labor
❓ FAQ
What are the four strokes?
Intake, compression, power, and exhaust. The piston makes two full up-and-down trips to complete one cycle.
How is a 4-stroke different from a 2-stroke?
A 2-stroke fires every crankshaft rotation and mixes oil with fuel, while a 4-stroke fires every other rotation and uses a separate oil system, making it cleaner and more efficient.
How long does a 4-stroke engine last?
With regular oil changes and maintenance, most modern 4-stroke car engines last 150,000 to 250,000 miles or more.