fuel gauge sender, Bench testing Options

[neilbardsley]

I'm having a problem with my fuel sender/gauge. The needle does go below half way. The light works to say the tank is empty.

I've had the sender out. I disassembled and cleaned.

The resistance is between 0 and 70 ohms. Which is I believe correct.

I put it back in but it's still not going below halfway.

Any ideas?

[Retroracer]

So that would point to either wiring or gauge being incorrect. 0 - 70 ohms is about right for the sender. Couple of things to check:

1) with the sender disconnected, take off the sender wire at the gauge. Measure the resistance to GND on the wiring. There should be none measurable (high impedance), BUT if the wiring has a resistive short to GND, then that would throw the "empty" reading off.

2) make sure the +12V feed to the gauge is fused, switched 12V - not via anything random or resistive (like a backlight bulb). It is always surprising how creative PO's can get with wiring "fixes"....

3) make sure the combo gauge has a GND connection to chassis (so it isn't trying to GND itself through the sender)

4) if the sender is disconnected from the gauge, with power on, does it read "empty"? If you then short the sender terminal to GND does it read "full"? If not your gauge is broken...

Hope this helps,

- Tony

PS. The obvious question: is your petrol tank half full? ;-)

[neilbardsley]

So that would point to either wiring or gauge being incorrect. 0 - 70 ohms is about right for the sender. Couple of things to check:

1) with the sender disconnected, take off the sender wire at the gauge. Measure the resistance to GND on the wiring. There should be none measurable (high impedance), BUT if the wiring has a resistive short to GND, then that would throw the "empty" reading off.

2) make sure the +12V feed to the gauge is fused, switched 12V - not via anything random or resistive (like a backlight bulb). It is always surprising how creative PO's can get with wiring "fixes"....

3) make sure the combo gauge has a GND connection to chassis (so it isn't trying to GND itself through the sender)

4) if the sender is disconnected from the gauge, with power on, does it read "empty"? If you then short the sender terminal to GND does it read "full"? If not your gauge is broken...

Hope this helps,

- Tony

PS. The obvious question: is your petrol tank half full? ;-)

Thank you. I will try those. The tank isn't half full (IMG:style_emoticons/default/smile.gif)

[Cairo94507]

I just replaced my fuel sender. It was sticking at 1/2 tank, 1/4 tank, 3/4 tank, you get the idea. Ordered one from Gaudin along with a new gasket and installed it the other day. Works like new now. NOS fuel sender was about $329. (IMG:style_emoticons/default/beerchug.gif)

[neilbardsley]

Ok. It's not the wiring. 1 ohms resistance on the wire from the gauge to the sender. Now it's reading 1/4 full if I turn the sender upside down. My son has a 1st Class Degree in EEE (first time he has been useful) so had a 100ohm resistor, which we measured at 80. We put this in between the gauge and ground wires nearest to the sender and the gauge empty! Therefore I need another 10-20oms from the sender?

I forgot to mention I had the sender apart and cleaned it. It's 4-69 ohms so maybe I need to clean again??

I did also buy a new vdo fuel sender. It doesn't have a separate circuit for empty and I haven't been able to get more than 5 ohms off it so I'm not keen to use it yet.

[euro911]

Here's a good thread on testing and refurbishing the sender unit:

http://914world.com/bbs2/index.php?showtopic=323753

[neilbardsley]

Here's a good thread on testing and refurbishing the sender unit:

http://914world.com/bbs2/index.php?showtopic=323753

Thank you. I had mine apart like that. The float moves freely and I cleaned some of the contact points but was reluctant to touch the wires as I've read they break easily. Im trying to talk my son into doing a resistance multiplier circuit

[Retroracer]

Neil - so it does sound like a sender issue. Presumably you tried shorting the sender terminal to GND on the gauge to make sure you get "FULL" indicated? 4 ohms or so on the sender sounds OK within error limits, I'd just make sure that 1) the float is not getting snagged, 2) the wires/contacts are clean and 3) and you measure 4ohms or less consistently every time the float is at the top....

- Tony

PS. I have a similar qualification to your son. Agreed: It does come in handy sometimes...! (IMG:style_emoticons/default/smile.gif)

[neilbardsley]

Thank you. Yes connecting directly to ground moved the gauge to full. The float does run smoothly.

I'm teasing my son. Most of his course was programming and maths. For his final year project he converted a medical laser from using analogue controls to a LCD display and control.

[seatosummit]

The warning light contacts are on the same float as the gauge sender stuff, so it is unlikely that the float is getting stuck.

It could be that there is a short or problem in the resistance wire inside the sender, or it could be that the gauge is wonky.

We tell people to always trust the light over the needle on the gauge.

--DD

Thanks Dave,
I will start looking for a new/used gauge.

Br,
Hans Jan

I have several fuel tank gauges. Cheap. What year is the car ? Silver dot center? The connectors on the fuel gauge are different. You can just replace the fuel gauge portion.
You can test the gauge by grounding the sending unit wire and it should peg the gauge.
Bruce

Hey bdstone914-

Do you still have fuel level gauges available? If so, I would love to buy one.

Please PM me.

Cheers,
Austin