Fuel Gauge

[RobMoore]

My fuel gauge is reading just over 1/2 when my tank is full, I removed the wire from the sender unit and earthed it reads same. Just got a new one (NOS) and it is pretty much the reading the same.
I have no idea now as I ruled the sender unit out and can't think what else could cause this.
Bad earth somewhere perhaps?

[nigelr2000]

Funny you should say that, when I have the lights on my fuel guage reads half when its full so I assume its a bad earth at the speedo end just not had time to check it out yet, mine is the old pre voltage stabiliser type. I will post if I get it sorted but I keep forgetting about it until its dark !!!! doh

[RobMoore]

hehe yes it is getting dark early now, I am going to have to get some lighting set up for my garage so I can still play in the winter.

[bmcecosse]

Couple of 500 watt floods works well - and provide good radiant heat too!

[RobMoore]

lol roy that would play havoc with my electric bill

[DAVIDMCCULLOUGH]

Have you had the sender unit out to check it? I had one were the plastic float had developed a wee hole and was weighted down with the petrol inside it, making it read less full!

[RobMoore]

Aye David I have examined the sender unit.

[MColes]

My fuel gauge only seems to update itself if you stop, turn the ignition off and back on again. Which could end up being a bit of a problem on a long trip

[Alec]

Hello Rob,

the next step is to get to the back of the fuel gauge, check, if you can, the supply, it should be about 10v then earth the instrument sender terminal to a good earth. If both those are good and the instrument still reads half, it's the gauge itself.
If you get full scale then it's a poor earth at the tank end or the sender terminals are suspect, it's matter of elimination.

Alec

[MarkyB]

My fuel gauge only seems to update itself if you stop, turn the ignition off and back on again.

You must have the early computerised version.

[polo2k]

no one has mentioned the tank to earth connection. maybe try earthing the signal wire on the boot floor instead of the tank its self

[RobMoore]

been out again this evening (Dark stops play again hehe)
I removed all wires from regulator and gave the spades a good clean then connected back up.
removed wire from sender unit and earthed it to body using the wing bolts as contact point gauge now reads 3/4
fitted new gauge and that also reads 3/4 with sender wire earthed to body.
So either I have 2 faulty fuel gauges or I need to look elsewhere

Earthing the gauge case? I am guessing this is provided by the 2 screws that hold the speedo in place?

1 thing I do know is that it aint the sender unit.

Im trying to think back to what I have done recently and I did change my fuel tank last month.
How is the fuel tank end earthed? its mounting bolts?

[Alec]

Hello Rob,

two different gauges reading the same seems to eliminate the gauge. Earthing of the instrument itself is irrelevant. Either your regulator or its supply is defective, or the sender cable is. From your post you don't mention earthing the instrument sender terminal directly, as this eliminates the sender cable ?

Alec

[RobMoore]

I'm not sure exactly where on the instrument sender terminal do you mean the spade on the back of the gauge?

[charlie_morris_minor]

Is the needle of the gauge free to move to the full mark? I seem to recall I bumped the gauge once putting the speedo back in and the needle would happily move most of the way across the gauge before it became "stuck".

[Alec]

Hello Rob,

yes that's exactly it. You just need a short piece of wire to touch that spade to earth.

Alec

[RobMoore]

Tested both of my fuel gauges earthing the sender wire terminal to earth and both are reading 3/4 full..
Both have full movement on the needle so does this mean it is my voltage regulator?

I have alternator fitted so perhaps I can even by pass this?

[PSL184]

The voltage reg supplys 10 volts to the gauge - you still need it even with an alternator (the voltage reg we are talking about is the small metal can bolted to the back of the speedo BTW not the box under the bonnet).....

[RobMoore]

The voltage reg supplys 10 volts to the gauge - you still need it even with an alternator (the voltage reg we are talking about is the small metal can bolted to the back of the speedo BTW not the box under the bonnet).....

ah fk then I'm now puzzled lol

[Alec]

Hello Rob,

its a small rectangular metal box with two terminals, one supplied from a fuse (green wire) and the other feeds the fuel gauge (light green\green wire). It mounted on the back of the speedometer.

It does sound as though that now is the problem although it could be a poor connection at the fuse end?

Alec