Testing fuel gauge

[snoddas]

Could I test if the fuel gauge work by ground the cable which attach to the sending unit. The fuel gauge should then read max value?

The sending unit have two pins, have both same sourse or is it + and ground?

The fuel tank selector switch read 6 V out when measure but its not constant, its flucturating from 0 to 6 V. Its that correct. This with start key in first position.

Thanks,
Anders
1974 bronco

 

[B RON CO]

Hi, you are on the right track. The instrument cluster voltage regulator sends a 6 volt pulse to each gauge, and each gauge sends the pulse to each sender. If the gauge is working it will go full sweep when you ground the wire. Good luck

 

[garberz]

You can check the gauge by grounding the sender, but don't leave the gauge pegged for more than a couple seconds. The IVR sends a pulsed voltage to each gauge, that's the + side of the gauge. The - side is the sending unit. It varies the resistance to ground, that's why the other side of the fuel sender is grounded to the frame. You shouldn't have any pulsed + voltage at the selector switch. The selector switch is part of the - side of the gauge. It just selects which sender to read the varying ground from. All three gauges, fuel, water temp, oil pressure are the same gauge with a 10-72 Ohm sweep. Just the faces are different. So they're interchangeable.

Mark

 

[snoddas]

Thanks guys for great and helpful information

 

[snoddas]

I took ground from my battery and Attach that lead/cable to the fuel sending unit cable. The gauge showed full.
Did the same with my other problem the temp gauge - same result.

I assume I need to buy new fuel sending unit and temp sensor. I will inspect the fuel sensor first, maybe the float or other which I could repair.

/Anders

 

[DirtDonk]

Is the tank and sending unit stock still? If so, you can also isolate the wiring to ensure it's not part of the problem.
Pull the rubber connector off of the sending unit (a stock one should look like this: http://www.wildhorses4x4.com/product/sending_unit_pigtail/Bronco_Fuel_Tanks) and simply jumper the two contacts together.
It sounds from the pulsing like your positive wire is good, but it still doesn't hurt to test. With the two contacts connected and the key on, you will get the same full gauge reading. This indicates that the positive feed and the ground are good.

You can test the sending unit too of course, but to do it correctly would mean taking it out of the tank. They often fail, so it's not out of the question. But they often just come out of adjustment too. So it's good to just pull it out to look anyway.
But with all that work, most people have a new one standing by and just put it in anyway.

With any new sending unit though, test it connected to the wiring before installing in the tank. This way if the float arm needs any tweaking to get the gauges reading properly, you don't have to pull it out of the tank again!

Good luck.

Paul

 

[DirtDonk]

Oh, and yes, the water temp sending units go out pretty often too, after this many years (if it's original still) so new ones are cheap and readily available to put in.

Paul

 

[snoddas]

Thanks a lot Paul. Hope to have it out of the tank tonigt.
Hoped rockauto have the fuel sending unit but nope. I'm an overseas buyer and often tricky to order from LMC and toms....

Will order new temp sender also

/Anders

 

[snoddas]

Is the tank and sending unit stock still? If so, you can also isolate the wiring to ensure it's not part of the problem.
Pull the rubber connector off of the sending unit (a stock one should look like this: http://www.wildhorses4x4.com/product/sending_unit_pigtail/Bronco_Fuel_Tanks) and simply jumper the two contacts together.
It sounds from the pulsing like your positive wire is good, but it still doesn't hurt to test. With the two contacts connected and the key on, you will get the same full gauge reading. This indicates that the positive feed and the ground are good.

You can test the sending unit too of course, but to do it correctly would mean taking it out of the tank. They often fail, so it's not out of the question. But they often just come out of adjustment too. So it's good to just pull it out to look anyway.
But with all that work, most people have a new one standing by and just put it in anyway.

With any new sending unit though, test it connected to the wiring before installing in the tank. This way if the float arm needs any tweaking to get the gauges reading properly, you don't have to pull it out of the tank again!

Good luck.

Paul

Paul, tested what you suggested and that also worked. Good ground I assume.

 

[DirtDonk]

Sounds good. So far the wiring seems intact and functioning.
The only hard-to-test component these days with all of us having digital multi-meters instead of the old analog sweeping needle type, is the IVR, or "Constant Voltage Supply" (funny name for something that pulses!) with it's varying output.
But the good news is that when you get all of the senders talking to the gauges, if you are able to verify their accuracy somehow and find them reading high or low (all three though, oil, water, fuel) you can make minute adjustments to the voltage regulator's output.
There is (on most of them at least) a tiny nub/thingy between the wire connectors that is an adjustable dashpot. Turning it clockwise increases output voltage and counter-clockwise decreases it. Raising or lowering the needle readings on the gauges.

But only fiddle with that if you note that all three gauges are reading slightly low or high consistently as a set. If they're not in synch, accuracy-wise, it's just the gauges or their individual wiring resistance values.

Hope the new ones work out for you.

Paul

 

[snoddas]

Sounds good. So far the wiring seems intact and functioning.
The only hard-to-test component these days with all of us having digital multi-meters instead of the old analog sweeping needle type, is the IVR, or "Constant Voltage Supply" (funny name for something that pulses!) with it's varying output.
But the good news is that when you get all of the senders talking to the gauges, if you are able to verify their accuracy somehow and find them reading high or low (all three though, oil, water, fuel) you can make minute adjustments to the voltage regulator's output.
There is (on most of them at least) a tiny nub/thingy between the wire connectors that is an adjustable dashpot. Turning it clockwise increases output voltage and counter-clockwise decreases it. Raising or lowering the needle readings on the gauges.

But only fiddle with that if you note that all three gauges are reading slightly low or high consistently as a set. If they're not in synch, accuracy-wise, it's just the gauges or their individual wiring resistance values.

Hope the new ones work out for you.

Paul

The fuel gauge its alive and kicking
Wonderful feeling. Scary thougt because I dident directly find any clear problem.
Switch to a new float, clean the contacts at the sender, also the pins that steer the sending unit in right position at the tank was bended. Now the sending unit is in correct postion. Also adjust the contact that run at the resistor inside the lid (sending unit).
Anyway, it works perfect and also the ohms its deliver seems correct. Have put in about 25 Liters and its read about half tank, the needle is steady and no leaks .

 

[garberz]

The fuel gauge its alive and kicking
Wonderful feeling. Scary thougt because I dident directly find any clear problem.
Switch to a new float, clean the contacts at the sender, also the pins that steer the sending unit in right position at the tank was bended. Now the sending unit is in correct postion. Also adjust the contact that run at the resistor inside the lid (sending unit).
Anyway, it works perfect and also the ohms its deliver seems correct. Have put in about 25 Liters and its read about half tank, the needle is steady and no leaks .

Good to hear it's working.

Mark

 

[snoddas]

Good to hear it's working.

Mark

Thanks Mark

 

[snoddas]

Today I install the new temperature sender/sensor. Now all gauges work. Turned out great. Thanks for all good advices.

/Anders Ohlin

 

[garberz]

Today I install the new temperature sender/sensor. Now all gauges work. Turned out great. Thanks for all good advices.

/Anders Ohlin

All your gauges are working? Well now you're just bragging!

Mark

 

[snoddas]

All your gauges are working? Well now you're just bragging!

Mark

;D;D;D think if the body could be that good - I have working gauges thought

 

[Hotfeet]

I am having similar problems.
I have a new switch and new wiring plugs on the tanks.
My gauge is pegged full all the time.
I am not sure where to look now.
Thanks

 

[DirtDonk]

Well, you could start by disconnecting the sending unit(s) at the tanks to see what the gauge does then.
If it stays pegged, then the problem is not at the tanks or sending units.
If it goes to zero, then it is in fact a sending unit or wiring issue. Well, not likely wiring when you narrow it down to the sender, but it's possible that there is a short inside the factory plug.

If they're aftermarket tanks with separate power and ground wires, then the fault lies within the sending units.

paul

 

[Hotfeet]

Thank you for the info and a direction to go.

 

[Hotfeet]

When I disconnect the front tank it stays pegged. The rear tank it goes to empty.
Btw it stays the same when I switch back forth between tanks. So I am still not sure about the wiring. It's original wiring, or i can say it's not modern aftermarket new stuff. This is an inherited issue so I can't tell it's correct or not.