To fix an object (usually mechanical) to a working condition in a haphazard way. Also known as doing a MacGyver on it. This can apply to any non working thing, to fix it in a nonconventional way. This term was created during WW2, in reference to the Germans who were referred to as "Jerries" as slang. Allies often came across hastily repaired objects left by the Germans hence the term Jerry-Rig came to be.
Tom Jerry-Rigged that engine so that it burns more fuel than it was designed to.