NC Fuel Gauge misbehaving

  1. My model of MX-5 is: __NC1
  2. I’m based near: __Kent
  3. I’m looking for technical help or recommendations on: __fuel gauge / sender

I have a 2007 model year NC1 2.0 Sport with the following symptoms:
Fill tank - drive 200miles, fuel gauge slowly drops to 50%.
I think wow my new ECU/remap is efficient.
Car runs out of fuel.
Gauge still at 50%
Take battery negative off
Put battery negative on
Fuel gauge now correctly showing empty with warning light on

Refil car - drive it for 4 days watching the mileage , same thing gauge stops a little higher this time at 195miles

Car still has a little fuel so before I run out I do the negative on/off trick again. Fuel gauge now shows empty with light on.

Feels electrical - I have just changed from standard ECU to ME442 and this didn’t happen in the last year I owned the car before this change but I didnt think the fuel gauge / sendor routes through the ecu ?

Suspect bad earth somewhere?


In line with most cars your fuel tank holds the pump and fuel gauge sender. The sender operates via a float which in turn rotates a potentiometer (pot), the pots are normally wire wound and can become dirty/worn over time and become unreliable.

Equally a bad connection on the pump/sender assembly could also cause unreliability.

I’ve not removed my NC fuel pump/sender so can’t help with how to get to it, suffice to say my wife’s Fiesta pump assembly (similar arrangement) needed replacing and it required the tank to be removed under the car. :-1::-1:

Refer your maintenance manual for how to get to it, on your car.

Others my have other failure options too.

Good luck


Thanks Roy - I guess I will have to take a peek at the process if cleaning all the earths today doesn’t help it. Another full tank gone in so will find out in approx 200miles!

Disconnect the battery and maybe pull the fuses systematically clean and replace.
Check for water ingress, usual suspect for dodgy electricals if you know below the windscreen, the grommets. Just something worth looking at although it usually affects more than the fuel gauge if you are unlucky to get any water near that fuse board on the A pillar.

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