Faulty Fuel Gauge / fuel float in a '69 1750 coupe ? !

[adriank]

Gary thanks for these tips, makes sense in regards to the adjustment of the sender to modify when the red light comes on and adjusting the speed of movement in the gauge.

My guage is actually jumping forward and backward a bit as I drive making me think i have a dodgy earth somewhere (which i have redone at the fuel tank) or inconsistent voltage. I can put include some resistence through the violet colour fuel gage wire as you described but i dont think that will solve my problem.

I plan to get the multimeter out and check some voltages, if its jumping around a lot i may need to look at a new voltage reg and/or earthing issues.

Adrian

[Gary Pearce]

Hi Adrian, the most likely causes are:
1) the float in the tank. If the plastic container (float) is full of petrol it fluctuates widely.
2) the spring tension on the tank unit resistor is not sufficient throughout the span, causing open circuits. Bend it in.
3) the earthing on the fuel tank (and or) the earthing on the back of the dash. Also the reliability of the battery to frame.
4) a faulty gauge. Both the tank unit and the instrument can easily be tested with a multimeter.
The voltage regulator will have virtually no effect.
The resistor (light globe) goes on the back of the instrument and will only help by dampening the needle a bit if all else is well . Trial and error to the globe wattage is required.

[adriank]

of course the float could be full of petrol

or the other items you have mentioned - will do some investigation and report back

Adrian

[magraith]

Guys, keen for some assistance here.
I am not getting any readings on my gauge in the console.  So far I have checked the float and tested the float on a multimeter. The resistivity does change with movement, So I am assuming the float is ok, also assume the tank is earthed and therefore the float. Couple of questions:-
- How do I test the gauge?
- Does anyone know the cable path back to the gauge?
- Any other checks to help would be great, using a feeler rod at the moment, very agricultural.
Thanks.

[Paul Gulliver]

Gary Pearce is the oracle on all things 105. Have a look at his post from a couple of years ago


http://www.alfaclubvic.org.au/forum/index.php?topic=1320.msg8199#msg8199

Gully

[Gary Pearce]

Pull the 2 wires off the tank unit (in the boot on top of the tank)
One wire is the red light, the other is the fuel gauge needle.
Turn the ignition on, earth out each of the wires in the boot (while disconnected from the tank unit) in turn.
Don't assume the tank is a good earth, try a little wire connected to a good body earth source as your connector.
Look through the back window to the gauge on the console if you can see it and you should see one wire deflects the gauge needle to it's maximum extent and the other will put the light on. Dab the earth wire on and off to see movement.
This test is completely safe at this stage.
Let me know how you get on and I will tell you the rest.

[magraith]

Thanks Gary, appreciate the guidance.

Will give this a shot tonight and see how it responds.

[magraith]

Gary,

Pulled both cables off the lugs and connected them to earth and "bingo" fuel gauge registered full and the backlight came on as well...So I am assuming it is the float device that is causing me the problem.

I have a replacement float, but it appears slightly different, and when I rig it up the gauge seems to be working in reverse?? 

[Gary Pearce]

Yes there is two different brands and (guess what) they work opposite to each other.
You must stick to the matching tank unit.
Next step.
1) Remove your old tank unit from the top of the fuel tank (6 screws)
As you pull it out, observe if there might be any fuel inside the plastic float cylinder. If so pry off the plastic float, and maybe use the one off your other tank unit. It will only FLOAT if it is completely empty.
2) Connect your special earth with to the body of the tank unit and connect your two wires back on the correct way.
3) Turn the key on and move the lever on the tank unit through it's ark, observing the gauge once again.
Be careful with the open fuel tank not to cause a fire.Cover it over with a rag, and in particular make sure all your electrical connections are firmly connected (particularly the earth wire) before you turn the key on.
4) If you don't get the correct response from the tank unit now, the tank unit is faulty.
I can generally pull them apart and resolder them, but I don't know where you are. You might be able to fix it too.

[1750GTV]

This seems like a common thing among older Alfa's, mine does it, and so does my brothers cars. Its almost like a game haha, see how high or low u can get it goin around a corner 

Mine has always been like this as well. You get used to the needle waving all over the place, and like you guys, I also use mine as a G-meter.

Chris

[magraith]

Gary,

Ended up ordering a brand new sender from Alfaholics.  Arrived in 10 days and plugged straight in! 

Gauge fully functioning in a matter of minutes. 

Based on all the advice, I think I will keep my timber dip stick handy to fine tune the float/levels.

Thanks for your step by step fault finding, great stuff.

Matt