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Suspect connection but.....?
Nash - 11/10/09 at 09:59 PM

Evening all,
I decided to put 20 litres of petrol in the Indy today, the first time I've put a real fuel load in. The fuel guage went the wrong way!

By this I mean instead of going up the scale it went right down.

Am I right in thinking the guage is wired back to front and I need to swap the wires over? Or is it something more?

As ever.............Neil

[Edited on 11/10/09 by Nash]

[Edited on 11/10/09 by Nash]

tomgregory2000 - 11/10/09 at 10:03 PM

it should be just a case of swapping the wires over.

However on my vdo units it doesnt matter which way round you wire it it works it out its self, clever eh

AdrianH - 11/10/09 at 10:04 PM

I would say that it is not the gauge that needs to change but the float sensor.

It may be that the resister on the float needs to be switched around so that when empty it reads high resistance going to low resistance when full, or the other depending on how it is now. Like switching the output and earth wires around on the sender unit.

Hope I have it correct.

Adrian

Nash - 11/10/09 at 10:09 PM

quote:
Originally posted by AdrianH
I would say that it is not the gauge that needs to change but the float sensor.

It may be that the resister on the float needs to be switched around so that when empty it reads high resistance going to low resistance when full, or the other depending on how it is now. Like switching the output and earth wires around on the sender unit.

Hope I have it correct.

Adrian


Thanks Adrian,

I'll try that first as its easier then getting into the back of the dash!

.........Neil

r1_pete - 12/10/09 at 07:53 AM

Do you have the sender in upside down??

blakep82 - 12/10/09 at 11:20 AM

doesn't the sender normally work on resistance? so it wouldn't matter which way round you wire them?

Brommers - 12/10/09 at 12:19 PM

quote:
Originally posted by blakep82
doesn't the sender normally work on resistance? so it wouldn't matter which way round you wire them?


Yes. All fuel senders (except rather rare capacitative types) are basically just different forms of potentiometers - i.e. variable resistors. As such, it doesn't matter which way you connect the wires, since the resistance between them will be the same.

Sounds to me like the gauge and the sender aren't matched. Some gauges, for example expect the sender to have a resistance of 10ohms when full and 180ohms when empty. Some senders have a resistance of 80 amps when the tank's full and 10 amps when empty. Use mismatched senders like this and the results are exactly what you describe - the gauge starts off full and goes to empty as you fill it up.

The only practical solution is to fit the correct sender. You can get the gauge rebuilt sometimes but it's not cheap.

02GF74 - 12/10/09 at 12:34 PM

wot they say.

you may not be able to swap wires round as there may only be one wire.

usuallly one end of the resistor is connected to groung via the sender body and t'other to the slider and is on an insulated tab.

so you have only 1 tab to swap - how ya gonna do that?

there may be a second tab, that is spot welded to the sender's body that is earthed via the metal tank - you would need to insulated the sender body from the tnak to be able to have 2 wires.

the way the sender is fitted, in the tank may mean the float arm moves in different direction to what is needed i.e. fitted updside down - further more, in the Ladn Rover world, there are senders that fit in same wya i.e. to the top of the tank but work in opossite directions.

finally as they say, the range of resistance of the sender may not match the gauge, this plagues us in the kit car world as we like to mix and match uncomaptible parts.

x_flow57 - 12/10/09 at 12:43 PM

Mine did exactly the same.

I removed the sender and twisted the float rod 180deg, refitted with the sender up the other way and it works a treat.

Nick

Nash - 12/10/09 at 06:09 PM

I swapped the connections over tonight.

The connections are as described above in that there is an earth and a slider insulated connector.

On swapping the wires (so fitting a slider connector to the "earth" wire and swapping over the two wires) I got the guage reading full.

I still suspect this is not right as when the ignition is switched off the guage drops to 3/4 full which is where I believe the level should be.

I'll keep at it.

rusty nuts - 12/10/09 at 06:56 PM

Had the same problem with my Greengauges supplied fuel gauge and sender unit, If you have the same sender (have a look at Greengauges website for assembly diagram) the resistor pack was assembled as per the diagram and worked backwards. Turning the resistor pack over and tweaking the float arm sorted it. Greengauges may?? have altered their website since