Q: Replaced the starter, it's spinning correctly but not turning the engine over

The starter requires a proper amount of voltage and amperage to engage the starter to the engine and turn it so the engine can be started. If you have a weak or bad battery or one of the battery cables is bad causing the slow starter turning speed.

In order to properly diagnose the cause the battery and the cables will need to be checked. The battery will need to be load tested to see if it can take a full load on it. Replace the battery if it will not hold a load. If the battery is checked okay then the cables will need to be checked using a multimeter to measure a voltage drop of each cable from the battery to the starter. Clean or replace any bad connection or cables.

If you need any help with this, consider YourMechanic, as they can run the necessary tests to pinpoint the electrical issue and make the necessary repairs to your car.