300ZX (Z31) Forums Dedicated to 84-89 ZCars otherwize known as the Z31's

Fuel Level Off By Alot

Old 04-27-2014, 07:31 PM
Registered User
Thread Starter
Join Date: Nov 2013
Posts: 3
Fuel Level Off By Alot

was always getting half a tank off with old fuel sender so went to pick and pull to grab another. put the second one in and it read no gas and gas light on. while i was up front buddy plugged in the old one and played with my fuel gauge and gave me a free full tank of gas.

unfortunately when i put the old one back on, it gave me a full read with low gas light on bright. is there a grace period for the gas to settle? i noticed that if i sit there the red line on the bottom of the analog gauge for gas goes down but not the big one. any ideas? did i skip a step in taking everything down?
JosephGiancarlo is offline  
Old 04-27-2014, 08:43 PM
Registered User
zxguy1986's Avatar
Join Date: Aug 2013
Posts: 1,103
I guess it depends on what replacement sender you used. My orig '86na sender worked perfectly for 20 years as long as I cleaned it every 5 or 6 yrs or so. It was a tower with a set of wires with floating resistors that sent the gas level to the gauge based on resistance in the wires, I guess. The wires themselves would get covered with black stuff, looked like carbon grit, and I cleaned them with cotton swabs and alcohol. Worked fine for 20 years.

Then it gave up about 8 yrs ago. Bought a 'replacement' and it fit in the tank fine but reads exactly 4 gallons too low. Still does. I think it was adjustable but I never took it back out of the tank to find out. When Betty nags me now, I know I have another 80-100 miles to go. Both whole-tank and 1/4 tank readouts work OK at the gauge, so the aftermarket sender works OK.

I'm gonna buy a recycled OEM sender from a junker here, only 90K on it. Try that. The replacement I have now would be fine if I can adjust it to read 4 gals higher.

So I can recommend a replacement sender if it's adjustable at the sender. If you can find an OEM sender with low miles on it you're probably better off. As long as you are reading low, you won't get stranded. Reading high: fix it or replace it.

Oh, yeah, there should be no 'grace period' for the readouts if they are reading 'resistance' to current flow - which is standard, I think. If you install with power off, it should read correctly with power on. Give the floater(s) a minute to find their level. Drive around the block. If it isn't correct at the gauge, you need to switch it out. And don't forget to disconnect, clean and reconnect every connector you find between the sender, the harness and your dash. A dirty connection can screw up anything.

Last edited by zxguy1986; 04-27-2014 at 09:24 PM.
zxguy1986 is offline  
Old 04-27-2014, 10:34 PM
Grumpy & Helpful
Join Date: Sep 2006
Location: Mill Creek WA
Posts: 1,415
I've replaced the sender on an 85T and my present 86T. Courtesy Nissan. no problem with either one. the old style with the iron bar with carbon traces inside an aluminum can not too good over 20 years. the new style have floats. be sure you get the one for the analog dash. the digi dash is slightly different. zxguy was lucky cleaning it off that he didn't erase the carbon trace.
rogerz is offline  
Old 04-28-2014, 10:01 AM
Registered User
zxguy1986's Avatar
Join Date: Aug 2013
Posts: 1,103
Hey, maybe that's what happened the last time I cleaned it. It completely failed to work after that. And the new one did have a float. Works fine except for the low read. It works both the full-tank and 1/4-tank indicators.
zxguy1986 is offline  
Old 05-05-2014, 05:19 PM
Registered User
zxguy1986's Avatar
Join Date: Aug 2013
Posts: 1,103
Fixed my '86na replacement gas gauge today - the Nissan one with the floats. It was reading 4 gals too low. I calculated that the floats were signaling from a position approx 1-3/8" too far from the bottom of the tank (i.e., too high in the tank) So I bent the arm of each float to extend 1-3/8" farther into the tank than before. Will get a fill-up tomorrow and watch what happens. Betty can save herself some wasted warnings if I figured it right She's been bitchin' non-stop for 28 years and never coughs or sneezes...
zxguy1986 is offline  
Old 05-05-2014, 06:18 PM
Registered User
PredatorZ's Avatar
Join Date: Apr 2011
Location: A Shady Tree in Boise
Posts: 1,032

brilliant,great idea bending the float, makes sense that some adjustment/calibration would be needed to get it spot on. I do love the dual gauges, really a simple but innovative idea, all mine have always worked (knock on wood).
PredatorZ is offline  
Old 08-10-2016, 08:09 AM
Registered User
Join Date: Jun 2016
Location: Livermore, CA
Posts: 16
Interesting read! In just over a month of owning my 87 NA Z31, I've never had the sub-gauge come down, but have managed to get about 360 miles before the gas light came on.

The main gauge never reads quite right. Always seems a little lower than I really have. When I full up, it's taken between 14.5 and 15.5 gallons (so I presume I still have about 4 gallons left in there with the gas light on).

I'm sure there's stuff I can do to clean the connections at the tank, but if I can at least consistently get 330-360 miles on a tank, I'm happy just using the trip odometer to eyeball things.

Should the gas light really come on with, like, 3-4 gallons left in the tank?
apexbuddha is offline  
Related Topics
Thread Starter
Last Post
300ZX (Z31) Forums
08-06-2013 02:02 PM
Vegas 350Z Club
05-02-2007 09:15 AM
280ZX Performance / Technical
05-03-2005 08:26 PM
81 Black L28E
280ZX (S130) Forums
04-13-2005 01:00 PM
240Z, 260Z, 280Z (S30) Forums
11-06-2002 07:38 PM

Thread Tools
Search this Thread
Quick Reply: Fuel Level Off By Alot

Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.