Gas Gauge
 

my Z gas gauge is off, in the sense of that it won't go to a full tank. It lies about how much gas is in the tank, and sometimes even says that there is none when there is almost a full tank...any ideas of how to fix this?

If it's the same as the sender in the 280's (and I think it is, but somebody correct me if I'm mistaken), then your sender is a triangular piece with wire wound around it, and the triangle points downward into the tank. The float moves a piece up and down along that triangle, which generates a different potential because of it's different radius. Works great until all the wraps of wire around the triangle come loose after 30 years and slide down the triangle, and you get exactly the behavior you mentioned, including odd 'dead' spots in the tank readings.
To fix it, get under your interior/floor panels back in the hatch area. On the actual steel unibody "floor" of the hatch area, likely towards the right side a bit, should be a roughly 4 or 5 inch circular piece held in by two screws. Remove the screws, and (carefully) peel/pry up the circular piece. It's seam/sealed and/or foam taped to the unibody to help keep exhaust fumes out of the car. Under it, you'll see a brass circular, toothed fitting ring, in the center of which is the sensor, and the two wires going to it. Unplug the sensor. Before removing: You're directly accessing your gas tank, you should be doing this in a well-ventilated area, nowhere anywhere near flames, pilot lights, smoking, or anything burning. Carefully use a screw driver and a mallet to counter clockwise undo the toothed lockring fitting. Now the sensor can come up and out. Check out those coils. They're probably all unevenly distributed on the triangular piece. Straighten them out and make them snug, and you can re-install. Make sure the fittings/gaskets are in good shape on the tank, or just replace them. Also be sure to really seal that circular access piece, too. Exhaust fumes in the interior are of course dangerous, and besides, it makes it smell like "old car".
If it's just not repairable, you can get a new sender, but otherwise you can have your gauge working correctly again for basically free.
good luck!
Dave

I'll have to take a look again, but if I recall correctly, the last time I went to fiddle with it, the fuel sender is on the side of the gas tank, right next to the differential, but I could definitely be mistaken. :)

Oh, well, that could be quite different then. The mechanism might be the same, just arranged differently in which case, it might be a similar and still very easy repair (hopefully).
Dave

yeah, hopefully, I'm going to take a look at it tonight after work.

Try courtesy nissan, I was on their page and they have a new gas sender unit for the first gen z for $36 :D mine has finally crapped because when I fill it up it goes to full then 35 or so miles later it goes to a half tank and stays there for about 120-160 miles then drops off at about 2 gallons left and if you are sitting in traffic you panic, especially if you are going uphill :mad: I am going to buy the new sender and hopefully that will fix it.
the sender basically works on elecctrical resistance to the position of the float in the tank