240zip Posted January 24, 2011 Share Posted January 24, 2011 My 240Z sat a while (year) while being restored. The fuel gauge seems to go from correctly showing the tank fuel level to zero. It was stuck at 3/4 full then I went over a bump and it dropped to zero, then it slowly moved up and then seems to drop down (quickly) and then slowing move up. What is likely wrong. Sending unit, wiring, fuel gauge? I'm tempted to replace the sending unit, but it will be a serious pain to drop the tank. Are there other likely culprits I can check first? Thanks in advance. Quote Link to comment Share on other sites More sharing options...
spitsnaugle Posted January 24, 2011 Share Posted January 24, 2011 My 240Z sat a while (year) while being restored. The fuel gauge seems to go from correctly showing the tank fuel level to zero. It was stuck at 3/4 full then I went over a bump and it dropped to zero, then it slowly moved up and then seems to drop down (quickly) and then slowing move up. What is likely wrong. Sending unit, wiring, fuel gauge? I'm tempted to replace the sending unit, but it will be a serious pain to drop the tank. Are there other likely culprits I can check first? Thanks in advance. *subscribed to see a solution.* I'm having a similar issue, but my fuel gauge stays on full till I turn the key off, then it moves down to E, in a jittery motion. The previous owner of my car "upgraded" the fuse box, so I'm not sure if thats the culprit in my instance. Quote Link to comment Share on other sites More sharing options...
Pharaohabq Posted January 24, 2011 Share Posted January 24, 2011 Sounds like a short(open)to me. I'd check the fuse box and the connections to it. the 240Z stock fuse box is notorious for having bad connections. The Fuel gauge operates on the amount of current flowing through the gauge, this is tempered by the adjustible resistor in the fuel sender. I don't remember if it's open that's empty, or fully closed that's empty, but likely it's open circuit that's supposed to show empty. So If you have a bad connection somewhere or your sender is bad it would drop to empty when you hit a bump and slowly go back up to the proper fuel level when the connection is re-established. As for poster#2 Spitsnaugle: It sounds like a shorted connection or bad sender to me, as above, your gauge is getting full current all the time. One way of testing this is to find the fuse that runs the fuel gauge, pull it and wire a temporary adjustible resistor (rhiastat)across the fuse slot, (CAUTION HERE: DO NOT SHORT THE WIRES TOGETHER WITHOUT A FUSE OR RESISTOR IN PLACE - Too much current could cause damage to your harness/gauge It should work that When you turn the resistor down, the fuel gauge should go up. if it doesn't then there's likely something wrong with the gauge. At least this is how I would expect it to work, since the gauge should be a circuit. Separately you could take the leads free from the tank and put the adjustible resistor there. (it would be wired in series with the fuse). Again changing the resistance to affect the gauge reading. this will tell you if your sender is dead or what... Phar Quote Link to comment Share on other sites More sharing options...
ThatGuyFromGates Posted January 27, 2011 Share Posted January 27, 2011 Just wanted to throw this out there as well- I had the issue of the gauge showing zero, with a full tank or empty. My car sat in the PO's garage for about 10 years before I acquired it, and I ended up dropping the tank to clean it out and found the sending unit "arm" attached to the float had rusted in the lower/empty position. Didn't take much to break it free, just that the new fuel in the tank wasn't strong enough sloshing around to break it on its own. Used some light sandpaper to clean the contacts and cleaned it with electrical contact cleaner, lubed up the pivot/joint and put it back in. Not sure if it is related to your problem or not- mine was just stuck all the time, but I just wanted to give my experience with that similar problem. Good luck, JK Quote Link to comment Share on other sites More sharing options...
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