VDO Fuel Gauge issue

[Firefly625]

Just saw TTL.s post on a similar subject, Here's my problem;

Fuel gauge always been fine, actually surprisingly accurate. But 2 weeks ago getting ready to go out (fuel gauge working fine & reading 3/4 at this point) & put my shore power lead in the cockpit locker on top of my fuel tank. The fuel gauge sender unit is bolted into the top of the tank with electrical spade connectors protruding with 2 wires coming from it. A little while later I saw fuel gauge reading empty, so realised I must have knocked one or both of the wires off the fuel sender unit when I put cable on top of tank. Lifted locker & indeed one of the spade connectors pulled apart due to the shorepower cable. Moved cable and plugged wire back on terminal...... Please to then see immediately the gauge starting to work... gauge rose from empty to 1/2 full, then past 3/4 mark, then past full, then carrying on round to end up about 10mmm over the full line, probably at the maximum extent of the little orange pointy bits range! Now I have unplugged both wires, re connected them, had a look at the back of the gauge, tapped it a few times with my finger (works in the movies!) but nothing will get it moving off MAX ............so has anyone experience of what might be up with my fuel gauge... by knocking the wires off did I/ could I have blown the gauge? Do I need to get the fuel tank sender unit out the tank and have a look at that, or just get new VDO fuel gauge...

the little blighter looks something like this!

.....
as always your help appreciated.
/forums/images/graemlins/smile.gif

 

[Philiz]

Don't know the answer but mine does the same. Suspect it's a sender problem rather than a guage problem. I just look at the tank to see how much fuel's in.

 

[jimg]

Does this help?

http://usa.vdo.com/NR/rdonlyres/CB2D00BC...eTypeSender.pdf

 

[Firefly625]

Hi Philiz...well yes, having a clear fuel tank does help!!

I just don't like things not working correctly, its my OCD!!

 

[Firefly625]

....oh, it may just help... what do you think, use up all my fuel, then see if it will adjust back to empty... certainly worth a try unless anyone else has any bright ideas, many thanks indeed!!

...now who has a plastic screwdriver! sounds as useful as a chocolate kettle! /forums/images/graemlins/confused.gif

 

[Peanuts]

Hi
Somewhere along the cables you are getting a direct earth back to the instrument via the 'G' cable.
If you look at the back of the fuel gauge you should see (excluding the light) 3 terminals, marked as +, - and G. The + is an incoming supply, the - goes to the fuel tank sensor and the G connects to the other terminal on the tank sensor (normally the centre one).
If you disconnect the terminals on the tank sensor and measure the ohms you should get between 10-200 depending on fuel state. If OK then reconnect cables on sensor and disconnect on gauge , measure ohms on cables, should be the same as on sensor. I am assuming the earth contact for the sensor is OK?
Try this for starters, hope it is of some help.

 

[Firefly625]

Peanuts, all suggestions useful. I think you might just be onto something. I will check this. Many thanks

 

[DAKA]

I could do to see a photo of your sender really.

The way they work........

Fuel gauge shows full as 12v goes through it.

As the tank lowers, the sender then adds residence to make the volts drop and your gauge goes down.

I guess as you knocked the terminal on the sender you have caused a loose connection on the sender top , if you are lucky it could just be a broken wire at the spade connector, I think you need to focus on the sender top first as that is what you have altered last.
First I would cut both spade ends off and fit new ones, I would then take the sender out and look for the loose connection within the sender, once the sender is out you can easily slide the sender to check if it works, no need to burn all your fuel to check it.
In other words if your gauge shows full all the time, then your sender is most likely bust and not the gauge.

 

[Firefly625]

[ QUOTE ]
I could do to see a photo of your sender really.

The way they work........

Fuel gauge shows full as 12v goes through it.

As the tank lowers, the sender then adds residence to make the volts drop and your gauge goes down.


[/ QUOTE ]

Hi Daka, thanks for that info. it had never crossed my mind as to how they work... simple really!

[ QUOTE ]
I guess as you knocked the terminal on the sender you have caused a loose connection on the sender top , if you are lucky it could just be a broken wire at the spade connector, I think you need to focus on the sender top first as that is what you have altered last.
First I would cut both spade ends off and fit new ones,

[/ QUOTE ]

This will be my first job. I am aware the wires seem to be a bit tight running to the unit hence why a small knock unplugged the connector. Also aware there is a lot of insulation tape around the spade connectors. I will re-new the wire and connectors and then go from there.. Many thanks
[ QUOTE ]

I would then take the sender out and look for the loose connection within the sender, once the sender is out you can easily slide the sender to check if it works, no need to burn all your fuel to check it.


[/ QUOTE ] - Oh, good point!!

excellent advice, many thanks /forums/images/graemlins/smirk.gif