When a catalytic converter is not working properly will it cause the engine to run properly?

A malfunctioning catalytic converter won't directly *prevent* the engine from running, but it can significantly affect how well it runs and may lead to further problems. It won't stop the engine from starting and idling, but you'll likely experience problems like:

* Reduced engine power: The exhaust system is restricted, making it harder for the engine to expel exhaust gases.

* Poor fuel economy: The engine has to work harder to overcome the restriction, using more fuel.

* Rough idling or stalling: The backpressure from the blocked converter can disrupt the engine's timing and performance.

* Illuminated check engine light: The car's onboard diagnostics (OBD-II) will detect the problem and illuminate the light.

* Exhaust smells stronger: Unconverted pollutants will pass through the exhaust system.

In short, while the engine might still run, it won't run *properly*. A faulty catalytic converter is a serious issue that should be addressed promptly to prevent more damage to the engine and other components.