Car smells like fuel? Leaks, stuck injectors and when to stop

What it means

Fuel reaches the engine under pressure, through lines, a rail and the injectors, sealed with O-rings. An injector that sticks open lets fuel flow continuously, so the engine runs rich: black smoke, a fouled plug and oil thinned with fuel.

An injector tip that leaks makes the engine rich at idle. A failed O-ring between the injector and the rail or manifold lets fuel out on the outside, where you may see wetness and smell it. Near a hot engine, escaping fuel is a fire waiting for a hot surface.

Common causes

• An injector stuck open, with black smoke, a fouled plug or oil thinned with fuel
• A leaking injector tip, which makes the engine run rich at idle
• A failed injector O-ring, with visible wetness around the injector
• Fuel pressure that is too high
• An external leak from a fuel line or fitting

What to do now

1. Stop driving as soon as it is safe, and switch the engine off.
2. Keep flames, sparks and cigarettes away from the car.
3. Do not loosen any pipe, rail, pump or injector to look for the leak.
4. Note what you saw: black smoke, a wet patch, or only the smell, and tell the workshop.
5. Have the car checked before it is driven again.

What the smell comes with

• A fuel smell with black smoke: rich running, so a stuck-open or leaking injector, or over-pressure.
• A fuel smell with visible wetness near the engine: an external leak, such as an injector seal. Stop, because it is a fire risk.
• Rich running without a visible leak: also a biased sensor or a purge valve stuck open.

What people often get wrong

That loosening a fitting is a quick way to check for fuel. A fuel system holds pressure after the engine is off, and on direct injection a jet at that pressure can penetrate skin. Leave every fitting alone.

When the car must go to a workshop

All work on fuel lines, rails, pumps and injectors: the manufacturer's procedure for releasing pressure, eye and skin protection, and a fire extinguisher within reach. None of it is an owner job.

Read next

• Exhaust smoke color: white, blue or black explained
• Clogged fuel injector symptoms, and the faults that look the same
• Flashing check engine light: slow down, this one is urgent

This page is general information and does not replace a professional assessment. Symbols, codes and behaviour vary between makes. Always check the handbook for your own car.