Fuel Gauge Reading Issues

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09-11-2020, 06:44 PM
RedCarsGoFaster

Fuel Gauge Reading Issues

My NSX has been out of action for about six months of this year, but on recommissioning it (with a new battery), the fuel gauge is behaving oddly.

When I fill the tank up to the brim, the fuel gauge needle doesn't seem to want to move above about 2/3rds full. I did briefly glance down on the motorway and see it indicating full, but very shortly afterwards the needle was pointing back to 1/2 full. After about 200 miles it showed a little below 1/2 full (plausible), and after a refuel to the brim again it's now currently showing just above 1/2 full. At this point I've lost faith in the gauge . . .

What's the most likely diagnosis? If it's likely to be a dodgy fuel sender I'll live with it for a bit and just refuel based on the trip meter, but if there's a possibility of electrical issues (gauge cluster caps? :eek:) then I might have to accelerate corrective action.

Google says total failures of the sender will manifest as the gauge reading totally full or totally empty . . . are there other sender failure modes that might match the behaviour I'm seeing?
10-11-2020, 09:08 AM
goldnsx

Quote:

Originally Posted by RedCarsGoFaster

...but if there's a possibility of electrical issues (gauge cluster caps? :eek:) then I might have to accelerate corrective action.

Unlikely that the caps are used in the circuit of the fuel gauge. But anyway, if not done already I'd recommend to change the caps on the gauge cluster.
Maybe a bad connector?
10-11-2020, 12:06 PM
Kaz-kzukNA1

If you didn't drive the car regularly and parked it for months with fuel level not close to full, most likely, the fuel level unit inside the tank.
Happened on several NSX.

Unlike the fuel pump, you can replace it without dropping the tank.
Surprisingly, no NSX name tax and the new parts is not that expensive (if ordered from Japan).

You can also check the sensor reading from the access cover behind the left side seat.
Despite the complicated structure of the level unit, the sensor itself is very simple.
Just a float at the end of a swing arm changing the resistance of the sensor unit.

Next time when you filled up the car to full or if you can estimate the actual tank level from the trip meter, try measuring the resistance.
At full, should be just a few ohm depending on the temperature.

When inspected the removed faulty unit, some of them showed correct resistance at first when the float was positioned at the full level.
Then, if you gently move the float arm up and down, the resistance fluctuated and showed much higher resistance at full level.

Inside the tank, when fuel level is not full, the unit/arm/linkage are exposed and not covered by the liquid fuel so can cause this issue.

Kaz
10-11-2020, 01:43 PM
goldnsx

Quote:

Originally Posted by Kaz-kzukNA1

If you didn't drive the car regularly and parked it for months with fuel level not close to full, most likely, the fuel level unit inside the tank.
Happened on several NSX.

Inside the tank, when fuel level is not full, the unit/arm/linkage are exposed and not covered by the liquid fuel so can cause this issue.

Kaz

Thanks for the info, Kaz. So I should fill it up asap...:)
Does it cure when filled up or is it kaputti?
10-11-2020, 07:22 PM
RedCarsGoFaster

Thanks Kaz!

Yes, the car was parked for several months with not much fuel in the tank, so it sounds like the sender is most likely to be my problem.

goldnsx - I have one of Heineken's gauge test units sitting on the shelf and am planning the gauge capacitor service for the New Year. I will probably replace the fuel tank sender at the same time.