What Causes Leaking Injectors?

Updated April 17, 2017

Fuel pumps create pressure in fuel lines. The pressurised fuel is forced into the head of the fuel injector held in place by O-rings. A solenoid in the injector charges and triggers a brief opening of the fuel injector valve. The fuel passes through the injector valve and is pushed through nozzles into a fine mist that is ignited during combustion. Leaking injectors create fire hazards, degrade performance and potentially damage engines.

O-Ring Damage

Fuel injector replacement and removal may damage O-rings. Installation of the injector into the fuel rail requires pushing the O-ring through a constricted space to properly seat the injector head in the rail. Improper seating and lack of lubrication on the O-ring causes damage to the O-ring material. Small cuts and cracks leak fuel under pressure. Always replace O-rings during fuel injector maintenance. Lubricate O-rings with a coat of new motor oil prior to installation.

Heat Damage

Overheated engines may cause O-rings to deform. Superheated rings expand beyond specification, then contract leaving gaps through which fuel passes. Replace O-rings on fuel injectors showing fuel leaks at the head of the injector.


Over time, fuel injector O-rings lose their capacity to expand and contract with the heating and cooling of the engine. O-ring material gradually hardens, reducing the capacity to resist pressurised fuel. Leaks developing at the connection to the fuel rail indicate O-ring failure.

Injector Valve Failure

Fuel injectors failing to close the internal valve will bathe the combustion chamber with a steady stream of fuel. Investigate engine codes indicating rich air-to-fuel ratios in specific combustion chambers. Rich ratios may indicate failed injectors. Fuel-bathed cylinders have reduced lubrication, causing premature wear and engine failure. Rich combustion may damage catalytic converters when non-combusted fuel burns in contact with the high-temperature catalyst.

Fuel Pressure

Fuel pressure beyond specification causes leaks at the O-ring connection of fuel injectors. Test the fuel pressure to determine if the leak is a result of too much pressure or general failure of seals.

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About the Author

Skip Shelton has been writing since 2001, having authored and co-authored numerous articles for "Disclose Journal." He holds a Bachelor in Science in education and a Master of Business Administration with an emphasis in management from Northwest Nazarene University. Shelton also operates a small automotive maintenance and part-replacement shop.