Magical Fuel Gauge

[Zyzym]

I had a funny thing happen with my fuel gauge in the last couple of days.
On Sunday night I had about 3/8ths of a tank of fuel and the computer advised that I had about 160 miles before I had to refuel.
On the Monday morning I had 5/8th of a tank and about 300 miles before needing to refuel.
The car has been locked up overnight and not used so I am at a loss to explain the change in the reading.
I had suspicions about someone getting caught short and relieving themselves but the fuel flap is intact and if they could pee that much they would be in the Guinness Book of Records.
I talked to the previous owner and he reckoned he had something unusual happen with the gauge a couple of times but was vague as to exactly what.
My other theory was that as I normally only travel in the car on my own but had a couple of friends in the vehicle that evening, whether or not this caused the car to sit slightly differently on the road which may have caused the float on the sender to move on a slightly different plane.
Has anyone any ideas as to how I can get this to keep happening?

[mjb]

If the car's facing uphill, it will under-read
If the car's facing downhill, it will over-read

Well known 406 flaw

[swiss]

The fuel computer on her indoors' Omega is pretty, um, fickle in its guesstimates. I don't set any more store by it than I do the ole' fashioned gauge on my 406. Rather, I reset the counter when I fill up then take 500 and subtract the miles shown to give the remaining range ^^

Speaking of which, got a tankful of the Morrison's biodiesel. 375 miles, tank still over half full. And that's with me driving like an idiot

[Zyzym]

If the car's facing uphill, it will under-read
If the car's facing downhill, it will over-read

I live in Peterborough. We don't do hills.
Car was parked in exactly the same spot as usual.
The gauge had been reading under ½ full for a few days prior. It now still reads above ½ since Sunday/Monday despite commuting to work.

[swiss]

Oh, and since my system started sucking air the fuel gauge has discovered a new trick. When you first start up it reads about 25% of what you actually have, then creeps up to the alleged correct reading over 20 minutes or so

Is there/has any one ever created any mods to obtain an accurate tank reading on a D8? If not it's something I'll consult with my instrumentation lecturer about...

[alladdin]

mine seems to discover an extra 1/4 tank now and then , it must be accurate at the fuller level as ive never ran out

[swiss]

Yes, absolutely. This last week and a bit the fuel light's come on every morning, sometimes with the needle actually below the orange square, yet I've managed to squeeze another hundred miles out of it.

[Doggy]

Yes, absolutely. This last week and a bit the fuel light's come on every morning, sometimes with the needle actually below the orange square, yet I've managed to squeeze another hundred miles out of it.

Costs that much to dispose of waste oil these days... maybe someone's giving you the odd top-up

[bangernom1cs]

These are notoriously unreliable.
I used to have to tap the gauge with my hand to get the correct reading. Caused by faulty soldering on clusters the PCB usually.
There was a friend of mine whose gauge always stopped halfway even when the tank was empty.
He got around it by filling the tank every shift and learnt to live with it.

T

[Johnny]

sorry to dig up an old thread, but i have the same issue. My fuel gauge generally won't work unless i hit the top of the dash or poke the glass covering the fuel gauge needle.

The PCB part which has been mentioned as being a flaw, does anyone have a link to images or threads relating to this, as its becoming a pest, and i've nearly caught myself short, trying to guess how many miles i have left

Thanks

[swiss]

Yes, there is a thread or two further down the board somewhere. It's a relatively simple job. You just remove the dash cluster then start taking bits off it until you have the PCB out. Then re-solder each and every joint, being careful not to solder in any short circuits.