So I have done my research about faulty old fuel gauges on z31s, I Had problems with my old cylindrical one falling to empty once it reached the halfway mark on the gauge..

last week I replaced the fuel sending unit with the new, updated, float type from here:

http://www.courtesyparts.com/25060-a...318_2340_2344&

this is the picture:



Initially the gauge read correctly or so I believe, since when I installed it, the tank had about 10 gallons in it.. of course, this is just a guess because I've never had an accurate gauge to begin with!
to make this short, the gauge rises and falls when I make turns, normal since the floats are installed sideways, but it seems that the level of gas doesn't drop below halfway! additionally, the quarter gauge drops to the halfway point as well when the car warms up but if left overnight, it goes up until the car has been driven and then goes back down to the middle.
the main gauge has sometimes also dropped all the way down but always comes back up to the middle....
when I add gas/ fill up, the gauge rises but again, never marks below the middle.

If anyone has any input, it would be very helpful. At this point, I think that the instrument cluster might have loose wiring or the fuel sending unit I bought is malfunctioning

couple things here. do you know how to use a multimeter? if you do, take the sensor back out and measure the resistance through the fuel pump module connector as you sweep the arm.
other thing is, with the sensor out and still electrically connected to the car, if you sweep it all the way does it move the gauge?
What you will need to is first with the sensor out measure the amount of resistance in ohms while sweeping the sensor. There should be no breaks in continuity and should steadilly increase or decrease depending on which way you move the lever. If that tests GOOD, measure the same thing at the back of the cluster. If your readings are good at your gauge you need a gauge, if there is a problem in between the sensor and the gauge run new wires, or if the sensor is acting screwy just change that. ... or just swap parts until you get it right :-)


http://www.motoralldata.com/alldata/...6495/145233316

I have no idea if that link is going to work for you, but it's a schematic of your fuel level sensor

OmEgA: Posting links to pay sites that require a login isn't very helpful. Especially since you can get the FSM free from several different sources. One of them being xenonz31.com

AmpedSilence: I would see if the floats are getting caught on something in the tank. Perhaps resting on the fuel pump?

the link didn't work but I ran these tests this past weekend on the FSU and it works fine... in fact, I turned the ignition switch to the on position, moved the floats while it was connected and the guage would work fine... I'll have to check the cluster soon. if I had another car, I could check it sooner

I didn't think to check for this. I guess I figured they would engineer the parts so it wouldn't interfere with other parts but it is worth checking out next time I have the chance. I have the floats facing to the left (driver) side of the car. The FSU would not turn to the right, it would get caught on something; perhaps the fuel tank's inlet tube?

I feel that maybe it could be the cluster at this point because it still has sudden drops in the gauge level reading but seems to still read the floats movements when going into turns.

AmpedSilence, I have the same problem with my fuel gauges.
When I fill the the tank, and drove it till a quarter of tank is gone, the fuel gauge start to shake and drop significantly all the way until the last quarter left of fuel it work OK. But I'm going to try to check to see if I could fix it.

You fix it by buying a new fuel level sending unit.

I have a analog fuel gauge on my instrumental cluster, and I have a broken fuel level sending unit. My question is would a digital dash fuel sending unit work on my car?
Thanks guys.
http://vintagezinc.com/images/300zxf...der_resize.JPG

i have a analog fuel guage on my 1987 nissan 300zx instramental cluster and my fuel sending unit is broken, and I want to asked if the digital dash fuel level sending unit work for my car?

This is the website that I was talking about Vintage Z Inc.
http://vintagezinc.com/images/300zxf...der_resize.JPG

Digital dash fuel level sender

DIGITAL DASH FUEL LEVEL SENDER

would it work on a analog instramental cluster.

Cuz my fuel guage is not digital its analog.

Thanks for the help.