Fuel Level Issue

[FANTOM P38]

Hi guys, hopefully someone can assist with this problem!
Since I purchased this car I have had a faulty fuel gauge reading. in that it would not show a full level or empty level?????, so in my wisdom I first replaced the fuel pump/sender unit in tank which seemed to improve situation a little, showing a slightly higher reading but it does not go to completely full or empty??????
So then I changed the fuel gauge, but problem persists.
Is there something I have missed or should look for?
Hoping someone else may have had similar issue & can offer advice where to look next.
I am also wondering if this may be affecting performance / economy, as I know as part of GEMS system the BECM takes into account fuel levels etc to adjust mixtues etc. Hope someone can throw some light on this as it has me puzzled & I would like to be able to trust gauge reading & range estimates etc!

[Fitzy2011]

All I can suggest is a bad earth somewhere, because both full an empty readings use only one thing in common, earth connection. If you can,t find it, try running a temporary lead back to a good earth location and see if that changes the Guage readings.

[davidsonsm]

Can you record the voltage signal at full and empty? I'll try to compare my readings.

Suggesting the obvious but, could the float be restricted in its movement. Probably not. Bad contact top and bottom of the potentiometer? Unlikely I'd say, especially if new. But probably worth checking the arm on the float. I've a spare float/pump unit if you want to try it? Let me know.

Don't know what else it could be.

[redandy3575]

I've got a similar issue in that I don't get a maximum reading most of the time, but do get a fairly accurate lower half reading. I'm guessing sensor reader playing up, I've had the occasional fuel gauge fault come up on the on display with a ignition off & on again reset.

Must be the P38 way of life. Never ran out of fuel as yet!!

[benji]

Found last easter if I stand there for 5minutes and dribble the last 10litres in it goes right up to full.

The gems ecu only uses the fuel guage to calculate km to empty, not the actuall fueling of the motor, so it won't be effecting economy.

[FANTOM P38]

Thanks for comments / suggestions guys, bad earth sounds like good place to start as it was similar thing with old sender so I may have changed it for nothing. Well at least I have spare now.
having taken tank out and put back in dont think it would be at that end so maybe an earth issue at gauges !! when I get time I will investigate further & update post.