Faulty fuel gauge, sender fix.

[Doone]

I've just updated The fuel gauge factsheet in the members area. It looks like its going to need another update soon.
http://www.igmaynard.co.uk/bongo/member ... sender.pdf

[jaylee]

Good point jaylee
I suppose it could be done all in one go, one wire from the sender and one from the chassis both connected to the earth, a bit of belt a and braces fix.

Indeed Dave, cut out the "middle man"... In this case the tank! It would be interesting to know (In the case of a dodgy reading on the gauge.) if the gauge gets more "flaky" when the tank is full... The weight of the tank adding to the earth resistance issue?

[missfixit70]

Not sure you can cut out the tank from the wiring loop?

From this thread - http://www.igmaynard.co.uk/bongo/forum/ ... =3&t=33920 - which also describes how to test the wiring/sender/gauge.

For a complete test of the fuel gauge wiring you will need a
cheap multimeter with a range of around 2K Ohms.

The tank sender unit is a variable resistor of around 0 - 100 Ohms.

0 Ohms = a full tank and 100 Ohms = an empty tank. You must
be able to estimate the approximate amount of fuel in the tank,
do not fill it to the brim, anything up to three quarters is best.

From memory, I think the sender resistance is linear and you can
calculate an approximate resistance value accordingly. ie. a quarter
tank should measure 75 Ohms and a three quarter full tank should
measure around 25 Ohms.

The positive supply to the sender is via the brass rivit which
fixes the tank connector to the fuel tank top plate.

The ground - or return path - is via the sender support metal
brackets bolted to the underneath of the fuel tank top plate.

Making sure that both measuring points are perfectly clean,
and the ignition is switched off, measure the resistance between
the brass rivit and the fuel tank top plate. If the sender unit is
in good condition then the measured resistance value should
correspond to your estimated value according to the amount
of fuel in the tank. If it continuously measures zero Ohms then
the sender unit is probably at fault, or the tank is full to the brim,
and you need to remove the top plate and test the internal
connections and resistor.

If this test proves the sender is OK, then simply short the two
wires - green and black - together, this simulates a full tank.
Switch the ignition on and the fuel gauge should slowly rise
to the maximum - full tank - position. If it doesn't do this then
you have a problem with the fuel gauge itself or the connections
on the PCB behind the instrument cluster.

If this test proves the fuel gauge and circuits are OK, then the
problem can only be corrosion between the fuel tank top plate
and the main fuel tank connector block.

As the eight securing screws for the top plate are sometimes
rusted away, it's worth replacing these with stainless steel
hexegon head set screws which you can easily tighten or
remove with a hex socket in the future.

Ben.

As I understand it, the tank not being earthed properly is what causes the issues with the gauge as the tank lid is the earth part of the circuit, so reinstating a good earth to the tank by whatever means should fix the issue if it's not a problem with the gauge or sender themselves, but it's getting late & it's been a long day, so I could be wrong?

[jaylee]

Not sure you can cut out the tank from the wiring loop?

From this thread - http://www.igmaynard.co.uk/bongo/forum/ ... =3&t=33920 - which also describes how to test the wiring/sender/gauge.

For a complete test of the fuel gauge wiring you will need a
cheap multimeter with a range of around 2K Ohms.

The tank sender unit is a variable resistor of around 0 - 100 Ohms.

0 Ohms = a full tank and 100 Ohms = an empty tank. You must
be able to estimate the approximate amount of fuel in the tank,
do not fill it to the brim, anything up to three quarters is best.

From memory, I think the sender resistance is linear and you can
calculate an approximate resistance value accordingly. ie. a quarter
tank should measure 75 Ohms and a three quarter full tank should
measure around 25 Ohms.

The positive supply to the sender is via the brass rivit which
fixes the tank connector to the fuel tank top plate.

The ground - or return path - is via the sender support metal
brackets bolted to the underneath of the fuel tank top plate.

Making sure that both measuring points are perfectly clean,
and the ignition is switched off, measure the resistance between
the brass rivit and the fuel tank top plate. If the sender unit is
in good condition then the measured resistance value should
correspond to your estimated value according to the amount
of fuel in the tank. If it continuously measures zero Ohms then
the sender unit is probably at fault, or the tank is full to the brim,
and you need to remove the top plate and test the internal
connections and resistor.

If this test proves the sender is OK, then simply short the two
wires - green and black - together, this simulates a full tank.
Switch the ignition on and the fuel gauge should slowly rise
to the maximum - full tank - position. If it doesn't do this then
you have a problem with the fuel gauge itself or the connections
on the PCB behind the instrument cluster.

If this test proves the fuel gauge and circuits are OK, then the
problem can only be corrosion between the fuel tank top plate
and the main fuel tank connector block.

As the eight securing screws for the top plate are sometimes
rusted away, it's worth replacing these with stainless steel
hexegon head set screws which you can easily tighten or
remove with a hex socket in the future.

Ben.

As I understand it, the tank not being earthed properly is what causes the issues with the gauge as the tank lid is the earth part of the circuit, so reinstating a good earth to the tank by whatever means should fix the issue if it's not a problem with the gauge or sender themselves, but it's getting late & it's been a long day, so I could be wrong?

Yep! there all the way Kirsty...

There maybe a gasket between the lid & the tank? (part 66-773A) http://lushprojects.com/bongopartsmk2/c ... o=.html#36 , but the through the screws should earth lid to the tank & the tank to chassis.....? So late or not? Take the earth from the sender to the chassis!??!!

[missfixit70]

Take the earth from the sender to the chassis!??!!

Which is what both of the "fixes" do isn't it? one works if you can access the top, the other is simpler & means you can do it from underneath with no dismantling/access issues.
As I understand it, the earth connection to the sender is not directly connected to the sender but is connected to the tank lid which is then connected to/part of the sender.
Is it not the earth connection at the end of the wire - to the tank lid that causes the issue?
so if I'm understanding you right, you would have to access the sender under the lid, connect an earth connection to that & then on to the chassis?
Seems to be over complicating it to me when there are 2 relatively simple methods that work?

[jaylee]

Take the earth from the sender to the chassis!??!!

Which is what both of the "fixes" do isn't it? one works if you can access the top, the other is simpler & means you can do it from underneath with no dismantling/access issues.
As I understand it, the earth connection to the sender is not directly connected to the sender but is connected to the tank lid which is then connected to/part of the sender.
Is it not the earth connection at the end of the wire - to the tank lid that causes the issue?
so if I'm understanding you right, you would have to access the sender under the lid, connect an earth connection to that & then on to the chassis?
Seems to be over complicating it to me when there are 2 relatively simple methods that work?

If the tank earth to chassis is the problem? Take out the equation...

Yep, another case where it can all go wrong... There should be a thread on that one too! I'll have a look & find it... (But that involves the use of sealant!??)

[missfixit70]

There should be a thread on that one too! I'll have a look & find it... (But that involves the use of sealant!??)

This one Jaylee? - http://www.igmaynard.co.uk/bongo/forum/ ... fuel+gauge - I'd forgotten about that one til you mentioned it Several different versions there of basically doing the same thing, ie reinstating the earth connection, be it via the chassis or via the earth lead between the sender & gauge.
It all depends on what access you have really & how in depth you want go into it, I'll stick with the simple methods personally

[jaylee]

There should be a thread on that one too! I'll have a look & find it... (But that involves the use of sealant!??)

This one Jaylee? - http://www.igmaynard.co.uk/bongo/forum/ ... fuel+gauge - I'd forgotten about that one til you mentioned it Several different versions there of basically doing the same thing, ie reinstating the earth connection, be it via the chassis or via the earth lead between the sender & gauge.
It all depends on what access you have really & how in depth you want go into it, I'll stick with the simple methods personally

That's the puppy!!

The way i look at it, if it can be repaired & money saved, (as opposed to the easy way like skipping for a new unit. Possibly the same amount of labour time involved?) however it's done!

There's a variety of no nonsense advice in layman speak, & examples in pictorial form on this forum regarding self help on a variety of different topics & problems that arise...!

....& yer all lovely people to discuss/"chew fat"/"bounce ideas" with!

All roads lead to Rome!

Keep it up ye all!

[missfixit70]

Tis what it's about , even if you do try & confuse me in the small hours
Always worth bearing in mind rule 10 of the T's & C's though - http://www.igmaynard.co.uk/bongo/forum/ ... 23&t=26157