Problem Investigation:  I took the Fiero to a master mechanic and we have deduced that the knock in the engine is being caused by a broken cam bearing that is blocking oil flow to the top half of the engine.  It's not an easy job to replace because the Fiero's design makes you have to take the entire engine out of the bottom of the car in order to replace the part.  The engine in a Fiero is in the rear of the car, behind the driver and passenger but also in front of the rear tire, making the Fiero a Mid-Engine rear wheel drive car.  The front of the car under the hood is reserved for the radiator, fans, spare tire, jack, and a place to slide in the tinted moon roof glass at the top of the car under the hood making it a mock "T" top.  The official trunk of the car is located in the rear of the car just behind the engine and rear tires.

The Broken Part:

Picture courtesy of: www.summitracing.com