So I went to fill my car up with gas for the first time since I put the engine into the car. The gas gauge only shows about 3/4 full, but the tank seems to be overflowing. Looking at the top of the fuel pump it appears to just be gushing out on the side pointing towards the rear. I left an absolutely massive puddle and trail of gas while leaving the gas station. This happened once before when I first started the car up. Is there a fix for this?

 

Pull the tank and fix it, or replace it.

 

Turns out I missed putting the blue o-ring in. With this in, then, should the gas station pump reach a stopping point? It seemed like it would pump forever before and just continue to overflow.

 

I have no idea what you are talking about with the o-ring but if the gas tank and vapor recovery is functioning properly the gas pump will stop when the tank is full.

 

There is a fuel cutoff safety feature that should be functioning on your Z. If the fuel tank and venting is properly attached, you normally pump fuel into the tank through a large tube until it rises enough to choke off a small venturi in the return line. Once this happens, air pressure rises and activates a cutoff built into the pump handle.

WARNING: if this isn't happening, you need to get your car inspected ASAP. Having fuel spilled in an uncontrolled manner is a serious fire hazard and should never be taken lightly.

From your previous threads, you are resurrecting two salvage Zs into one car. There's a myriad number of reasons why your gas tank could be overflowing and one blue o-ring may, or may not, be the reason. From what you're describing, this could be a disaster waiting to happen and none of us can help you from behind a keyboard. Get a qualified tech to inspect your car ASAP!!