When you were changing the oil in your Mazda rx 8 cranked it with cap off now check engine light is ondid i hurt engine?

It is unlikely that you have hurt your engine by cranking it with the oil cap off. While it is not ideal, it is not typically a cause for major concern. The oil cap is there to prevent oil from splashing out of the engine, but it does not create a seal that is critical to the engine's operation.

When you cranked the engine with the oil cap off, some oil may have splashed out, but it is unlikely that enough oil was lost to cause any damage. The engine's oil pump will continue to circulate oil throughout the engine, even if the oil cap is off, so the engine will still be lubricated.

The check engine light is likely on because the engine's computer detected a drop in oil pressure when you cranked the engine with the oil cap off. This is a normal safety feature that is designed to protect the engine from damage in the event of an oil leak.

You can reset the check engine light by disconnecting the negative terminal of the battery for a few minutes. This will clear the computer's memory and turn off the check engine light.

If you are concerned about the engine, you can take it to a mechanic for an inspection. The mechanic can check the oil level and pressure, and look for any signs of damage.