I have a 2003 Manual Nissan 350z. So I was rewiring my 02 sensor pigtail attached to the test pipes on the driver side and as I was trying to take off the old sensor I heard a loud explosion and found this puddle on the ground right after. My car hasn’t actually ran in a year and I’m slowly fixing it so this is just another set back for me. I really need help on what this is. The smell isn’t fuel and I highly doubt it’s a fuel line because the car started right after. Someone please help!!!

 

Ignoring the explosion comment for the moment, was it on the passenger side and do you have the AC working? Could just be condensation off of the coils.

 

It seems to be on the passenger side and I don’t even know if the ac even worked.

 

Without hands on, it's anyone's (here) guess. Start by analyzing the fluid. Oil based? Water based? Look at the liquid spill again on the floor? Is it still there as liquid or did it evaporate? That should tell you a fair amount.

Also, if there was indeed an "explosion", there HAS to be a fluid trail on the car. Shouldn't be hard to find that much fluid leakage and trace to the source.