Fuel gauge issue, won't read right.

[jeb820]

Hey guys me again. Having issues with my fuel gauge it won't read correctly. I have a 70 lt underfloor tank (poly dealer installed). I didn't get them to put in a fuel gauge as I thought the option was over priced and I wanted to do the modding myself. So I purchased a VDO fuel gauge off whitworths, wire her up and was pleased with myself when it read 1/4 full. however went to the fuel station today and fueled her up. Stupid gauge still reads 1/4 full. having surfed the web a bit, seems like there are no standard gauges you need the right one for your sender. is this correct? and how do I know what is the right one?

Im thinking a fuel sensor for my sounder might be a better option

[DvrDve]

is the gauge correctly wired up? is it working, could u get another one from whitfords to try
mine has 4 positions for hooking it up-oldish unit
when i redid wiring worked out it gave me an option to calibrate- had to empty tank connect her up to position 1/4 then fill up and connect to wire 2/4
3/4 is for std operating
sadly i dont have the instruction manual

i also have a fuelflow sensor which is great as long as u
-remember to input amount, every time u fuel up
-work with known qauntities-the almost half full jerry -litre or 2 here and there
eventually adds up and u dont know where u are

though easy enough overcome if u know ur tanksize and fill up to brim
i have heard of ppl having trouble with their inline senders sticking/blocking fuel flow -never on mine (yet touch wood)
i love it as it allows me to get to finetune my trim, max speed /min fuel

[jeb820]

the gauge is brand new, after testing it a few different ways I believe I can rule out a faulty gauge. I followed the wiring diagram that came with the gauge so It should be wire up correctly.

I am thinking that the ohm rating of the gauge doesn't match the ohm rating of the sender, going to buy a multimeter today to find out.

[Gravy]

What type of sensor are you using, is it a float operated mechanical device or a capacitance sensor? If its the former in the tank measure the float arm travel distance from a full to empty tank.

The performance of the gauge can then be determined without filling or draining the tank. With the float displaced to the empty limit the gauge should read empty, if it isnt your problem is a zero off set in the calibration, there should be a facility to adjust this.

Once you have zero set correctly, displace the float to the full travel position, the gauge should read full, if it isnt the span of measurement requires adjustment. Often zero and full span adjustment interact with each other you may have to carry out the zero to full process a number of times to obtain an accurate result.

Hopefully there is facilities on the sender to set the float displacement stop limits, especially for the empty position.

If its a capacitance type sensor its a whole different can of oranges and you will need good documentation to calibrate the gauge.

Apologies for the long winded explanation its my instrumentation background raising its ugly head.

Gravy

[jeb820]

I have no idea what type it is. I have look for information stickers on the tank but have not found anything saying what type or ration the sender is. the tank is sort of see through plastic but it is pretty much full of fuel so can not anything much. the tank comes from santmarine so I my have to hit them an email for some info.

[BarryJ]

Is this what the unit looks like (from the Whitworth's on-line catalog):
http://http://www.whitworths.com.au/products/34122_lg.jpghttp://www.whitworths.com.au/products/34122_lg.jpg

If it is, it looks like a float arm mechanical device as described by Gravy and you will need to calibrate it as he suggests (i.e. set the float at zero and full).

[BarryJ]

And from the VDO site:
http://www.vdo.com/generator/www/com/en/vdo/main/products_solutions/special_oem_solutions/fuel_management/adjustable_lever_type_sender/img/img_adjustable_fuel_lever_arm_sender_detail_192_en ,property=original.jpgBenefits


Adjustable fuel lever arm sensor
Versions with and without warning contact
Ø 54 mm – standard flange
3 different resistor ranges (thick film technology) for operating
standard gauges (depending on customer requirements other resistor ranges may be specified)
Support of various tank depths via easily adjusted lever arm
Robust design
Long life, redundant contact system
All metallic parts in stainless steel
Float made from NBR – float will not sink if damaged
Electrical connection protected by socket housings
Flexible mounting geometry using elongated holes
Defined movement of lever arm for extended service life – e.g. protection against wave impact on boats over a long time
Resistor element with an extended lifetime (1million cycles ‘full/empty’ in Super unleaded fuel)

Blue Highlight added by me.

[jeb820]

Ok so the sender came with the tank so I have no idea what it looks like except what I can see from the top. It doesn't seem to be threaded in, I tried to unscrew it but felt like I was going to bust it. from what Ive read most marine senders work in a ohm range of 33 - 240. 33 ohms when full and 240 when empty. The gauge I bought (the cheapest I could find at the time, didn't realise there were different ones) has an ohm range of 0 - 180. I bought a multimeter this morning checked the resistance of the tank and it read 34 which would put it in the 33 - 240 range (cause the tank is all but full)

So conclusion is = I HAVE THE WRONG GAUGE DAM IT,

$50 down the drain pipe.

Pic of top of sender

Pic of Gauge when wired up as per instructions

Pic of Gauge with sender wire off comfirming gauge is functioning

[BarryJ]

For starters, I would try to return the gauge because you have made a genuine mistake; worst they can say is no BUT you might get a refund. If you don't ask, you are definitely down the drain.

Next step is as you have already suggested is to contact the tank manufacturer to see what sort of sender unit has been installed and hopefully get a bit more info.