Hi there,

I am reasonably good at electronics and working on cars, but i have a fault with my vauxhall corsa.

The fuel gauge is bouncing when driving along.

I have shorted two wires together, and this makes the gauge go right up to full, and then i disconnect this jumper wire the gauge falls to nothing.

Once connected the wiring must be supply a resistance to the fuel gauge as it moves the needle, it is only once driving that this fault occurs.

I have read on the internet this seems to be a reoccuring fault with this model of vehicle.

I have also read changing the sender unit doesn't always cure the fault.

So I am wondering is there a circuit i can make, or a circuit that already exists that would:
Take the resistance over a period of seconds / minutes, and then put out an average resistance rather than a constantly changing one?

This is something which i am guessing would have to be computed by a microcontroller or some such?

Has anyone got any advice?

Cheers
Paul

I thought it was being computed and averaged already by the engine management system for the onboard trip computer stuff...perhaps not in your case. Check all the connections, wiring et all from the sender to the dashboard at least, one of em will most likely prove to be dodgy.

Modern cars are very poorly wired in my opinion, it really is a case of where what's cheaper, is not necessarily better now. I think in the last 10 years or so virtually every electrical fault I have looked for in a car for a friend, has turned out to be either bad wiring, or dodgy connectors. When I say bad wiring, I mean actually broken internally, sometimes due to corrosion, sometimes due to not being properly dressed. Only a few times has it actually been a faulty transducer, sender or sensor at fault. While modular wiring is great in it's concept, the rough environment that a car presents is not the place where I would consider it a great idea, the manufacturers see it as a revenue gravy train for their dealers service departments...

yeah i will do the wiring checks but have a feeling the wiring is going to be ok, like i said when i put a wire between two pins on the sender connector it makes the dial gauge go to max, then when i take it off it drops, and i imagine if i put a resistor between the two it would read X amount of fuel..

i actually dont think this vehicle has a computer averaging the signal at all. it's a shame really.

Originally Posted by drage

i actually dont think this vehicle has a computer averaging the signal at all. it's a shame really.

I have a Corsa, and a Haynes manual.

According to the manual, there's just two wires from the sender, a ground wire and a single wire to the instrument panel. The instrument panel has the fuel gauge and a circuit to light the warning lamp.

I'd bet that you have a poor earth connection somewhere by the tank.

that being the case, i.e his corsa not having the fancy trinkets on it...then his fault could well lie within the dashboard panel as well as the body earth for the tank...
If it is an analog gauge on the panel, it is possible, I have seen it before, but not on a Vauxhall, that the winding for the meter movement had one end broken off...but still touching the wiring post on the meter. The winding terminations had no slack in them, and just being bumped about snapped it clean at the wiring post. So if the wiring shows up nothing, maybe a careful inspection of the actual meter movement, and perhaps the shunt resistor that goes with it might be in order...

cheers, never thought about the tanks earth, this sender has 4 wires, two for the low pressure fuel pump and two for fuel gauge but will investigate further..

ta