I need some fuel sending unit experts please

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bacchustn

bacchustn

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neptune beach (jax), Boca raton, FL
Help, I desperately need some help with my fuel gauge issues. I have read every thread that I could find on this topic in FABO and have a good working knowledge of the system but not a solution to my problem. The car has been in the process of being worked on for the past 15 years and was not driven until last week. All new fuel components from tank to fuel lines to filler tube to fuel pump.

My temperature gauge works perfectly. My fuel gauge and oil pressure gauge shows zero reading. I have the type of IVR that attaches to the fuel gauge only

New fuel sending unit installed complete with ground strap yesterday. Old unit bench tested fine after removal. With Key on, I am getting fluctuating voltage at the sending unit connector but it varies by timing and voltage. When grounding out fuel sending unit connector, the fuel needle at instrument panel goes to full. Double checked and I’m getting good ground at the cover plate of the fuel setting unit.

Removed the dash panel And soldered all pins to board (several of which were loose). Also cleaned all connections.

1710181966510.jpeg


1710182047543.jpeg


My main question is it possible for the IVR to function well enough for the temperature gauge to work, but not well enough for the fuel gauge? Will the fuel gauge function if the IVR is alternating voltages, but doing so in a way that it is outside of the function of the fuel gauge?

My plan at this point is to install a solid state IVR and disable the internal fuel gauge IVR. Is there anything else simple that could cause these issues that I can be missing?
 
Random thoughts. The IVR in the gas gauge may be behaving inconsistently. Have you confirmed that the gauge cluster is grounded to the body? You may have two problems, fuel sending unit (chinesium) and temp sender ( taped threads?) I tend to think that your new fuel sender is bad because you can ground the sender wire and the gauge works.
 
Main Page - rte Solid state replacement for your ivr in the gas gauge. The factory unit is supposed to cycle to provide an average of 5 volts. When mine failed it stuck closed and pegged the temp and fuel needle. You can simulate 5v with 3 aa batteries taped together in series and see how the needle deflects seeing as you have the dash out.
 
Murray said:
Random thoughts. The IVR in the gas gauge may be behaving inconsistently. Have you confirmed that the gauge cluster is grounded to the body? You may have two problems, fuel sending unit (chinesium) and temp sender ( taped threads?) I tend to think that your new fuel sender is bad because you can ground the sender wire and the gauge works.
Click to expand...
I’m not sure about the grounding to the gauge cluster but I assume it is, because instrument lights work and temp gauge works. There is a large ground wire on the steering column and I understood the dash grounds through the mounting hardware. The fuel sender is brand new from classic industries. I bench tested it before I installed it. The old one I removed had been installed in the new tank about 10 years ago and has was only recently run through it. It tested the correct resistance after removal.
 
69conv said:
Main Page - rte Solid state replacement for your ivr in the gas gauge. The factory unit is supposed to cycle to provide an average of 5 volts. When mine failed it stuck closed and pegged the temp and fuel needle. You can simulate 5v with 3 aa batteries taped together in series and see how the needle deflects seeing as you have the dash out.
Click to expand...
Thanks, that’s the one I was looking to buy but I think their web site’s order page is down.
 
They read full and empty correctly (sometimes with a little bending of the float wire) but anything in between is in accurate. The tank isn't the same volume at the top as it is at the bottom, and the original sending unit is wound to correct. The new ones are wound for a tank with the same volume at the top and bottom.
 
Sorry, but you misunderstand the circuits so are barking up wrong trees.
bacchustn said:
My temperature gauge works perfectly
Click to expand...
Then the IVR is working.
bacchustn said:
My fuel gauge and oil pressure gauge shows zero reading.
Click to expand...
OK. Lets keep that in mind and see what they may share.
(Check the oil pressure gage conenctor and be sure its not grounding somehow)
bacchustn said:
I have the type of IVR that attaches to the fuel gauge only
Click to expand...
Rally dash. Goes along with having oil pressure gage.
bacchustn said:
ith Key on, I am getting fluctuating voltage at the sending unit connector but it varies by timing and voltage.
Click to expand...
That's how the IVR works. It provides an average voltage of roughly 5 V by the bimetal contact opening and then cooling and reconnecting.
video showing the pulsing on an analog meter while bench testing
bacchustn said:
When grounding out fuel sending unit connector, the fuel needle at instrument panel goes to full.
Click to expand...
Please don't do that for more than the briefest period of time! That will burn out the gage.
Put a 10 to 12 ohm resistor on it between the connecting wire and ground. That will simulate a full tank.
 
10 ohm resistor between the Oil pressure gage connector and ground should bring the gage to H or approximately 80 psi
22 ohms resistance should bring the pressure gage to show middle, and anything over 75 it should show zero.
So either high resistance or no connection would keep the pressure gage from working.

PS. Like the fuel gages, replacement oil pressure senders aren't matched to the '60s gages.
 
Mattax said:
Sorry, but you misunderstand the circuits so are barking up wrong trees.

Then the IVR is working.

OK. Lets keep that in mind and see what they may share.
(Check the oil pressure gage conenctor and be sure its not grounding somehow)

Rally dash. Goes along with having oil pressure gage.

That's how the IVR works. It provides an average voltage of roughly 5 V by the bimetal contact opening and then cooling and reconnecting.
video showing the pulsing on an analog meter while bench testing

Please don't do that for more than the briefest period of time! That will burn out the gage.
Put a 10 to 12 ohm resistor on it between the connecting wire and ground. That will simulate a full tank.
Click to expand...
Just touched it briefly with someone watching the gauge to see if the gauge responded.
 
Mattax said:
10 ohm resistor between the Oil pressure gage connector and ground should bring the gage to H or approximately 80 psi
22 ohms resistance should bring the pressure gage to show middle, and anything over 75 it should show zero.
So either high resistance or no connection would keep the pressure gage from working.

PS. Like the fuel gages, replacement oil pressure senders aren't matched to the '60s gages.
Click to expand...
Thanks for the response.

So that is the problem I’m having. The tests I’ve done on the fuel system show the fuel gauge, IVR, sending unit and ground are all good. Wherein does the problem lie? Is there a separate ground on the rally dash that could be missing?

I did not test the oil pressure unit other than temporary grounding to see if the gauge needle responded. (No movement)

The voltage test on the IVR at the fuel sender connector was done with a power pro ( alternated positive negative) and separately by digital multimeter. This produced a broad range of voltages at various intervals but nothing that looked like consistent intervals.

Is it possible for the IVR to be partially functional ( enough for temp gauge but not consistent enough for fuel and oil pressure-both of those aftermarket items)
 
IMO, people put too much worry into the fuel gauge reading dead nuts on. Yes, the aftermarket senders are not "perfect" in some cases, but guess what? Neither were the factory senders and gauges, either. They are all approximations to give you some idea of when you might be walking on the side of the road. The simple rule I live by is this. As long as the fuel gauge reads correctly when it's close to or on EMPTY, that's good. Honestly, when you stop and think about it (and most don't because they just want to argue) that's all that matters.
 
bacchustn said:
The voltage test on the IVR at the fuel sender connector was done with a power pro ( alternated positive negative) and separately by digital multimeter. This produced a broad range of voltages at various intervals but nothing that looked like consistent intervals.
Click to expand...
I do not understand how you used the power probe.
Please explain.,

I don't know what digital meter could possibly show as it struggles to display the rapidly changing voltage unless it has a scope function.
It's not really a square wave.
Did you watch the video?
 
bacchustn said:
The tests I’ve done on the fuel system show the fuel gauge, IVR, sending unit and ground are all good. Wherein does the problem lie? Is there a separate ground on the rally dash that could be missing?
Click to expand...
I really think you are missing how the gages work.
They do not ground. They should not be grounded.
The IVR gets a ground. That's it.
Lemme find the MTSC which should illustrate this.
bacchustn said:
I did not test the oil pressure unit other than temporary grounding to see if the gauge needle responded. (No movement)
Click to expand...
So there's there's two possibilities, there's an open or high resistance.
Open could be the gage unit itself is burned out, the unit isn't getting power, or a break or misconnection or high resistance connection anywhere along the way to the sender, or even in the sender.
bacchustn said:
Is it possible for the IVR to be partially functional ( enough for temp gauge but not consistent enough for fuel and oil pressure-both of those aftermarket items)
Click to expand...
Yes an IVR that has weakness or high resistance could restrict the current available.
Since everything is in the car, I think the easiest thing to do may be to get some 10 or 11 ohm resistors, and since they are cheap enough, grab some 22 and larger.
In the meantime see if there is any voltage at the oil pressure sender and then at the multi-connector on the bulkhead cavity for the oil pressure gage. Check that on the inside too if there is none. My guess is if there is none, then the gage may be burned out. @RedFish posted that he'd seen that happen when the oil pressure sending wire would get accidently grounded when loose (because the plastic connector covers frequently get lost).
 
Mattax said:
Lemme find the MTSC which should illustrate this.
Click to expand...


In the illustration, the IVR gets power from the connection on the left.
1710203697656.png


When power is available, electrons move and we say current flows from the power supply to the ground.
Lets show the current from through the IVR.
Some electrons go through the resistance wire (heating element) to ground, and others continue to the gage and sender if they are connected.

1710204319427.png

Its the heating element that needs the ground. For the rally IVR this ground is on the back of the gage as seen in this thread.

When the bimetal gets hot enough it breaks the connection.
1710204859962.png


Over time the input from the "12 volt system", really 14 V when running, results in output from the IVR that averages about 5 V over time.
1710204536022.png


My apologies if going over the IVR seems extraneous. The point is the ground at the IVR is for the heating coil, and each of the senders gets grounded to complete their circuits. So flow is like this.
1710206255339.png



from here Thermal-Electric Gauges (Session 227) from the Master Technician's Service Conference
 
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Mattax said:
I do not understand how you used the power probe.
Please explain.,

I don't know what digital meter could possibly show as it struggles to display the rapidly changing voltage unless it has a scope function.
It's not really a square wave.
Did you watch the video?
Click to expand...
The power probe shows power or ground. When attached to the sending unit connector it alternately flashes ground / power. Alternating but not consistent tempo. I don’t have an analog voltmeter. But the digital showed voltages alternating somewhere between 12 and zero. I can test again with a resistor.

Wouldn’t the fuel gauge needle moving toward full during the brief grounding show that the fuel gauge is not burned up?
 
bacchustn said:
The power probe shows power or ground. When attached to the sending unit connector it alternately flashes ground / power. Alternating but not consistent tempo. I don’t have an analog voltmeter. But the digital showed voltages alternating somewhere between 12 and zero. I can test again with a resistor.
Click to expand...
Thanks! You could use that power probe on the oil pressure sending unit wire too.
bacchustn said:
Wouldn’t the fuel gauge needle moving toward full during the brief grounding show that the fuel gauge is not burned up?
Click to expand...
Yes.
It's the oil pressure gage that might be burned out. Hopefully not. I'm hoping something simple like a terminal not connecting. I know its a pain taking the panel out.

With the panel out, you can check each gage for resistance before testing with power.
 
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bacchustn said:
Thanks for the response.

So that is the problem I’m having. The tests I’ve done on the fuel system show the fuel gauge, IVR, sending unit and ground are all good. Wherein does the problem lie? Is there a separate ground on the rally dash that could be missing?

I did not test the oil pressure unit other than temporary grounding to see if the gauge needle responded. (No movement)

The voltage test on the IVR at the fuel sender connector was done with a power pro ( alternated positive negative) and separately by digital multimeter. This produced a broad range of voltages at various intervals but nothing that looked like consistent intervals.

Is it possible for the IVR to be partially functional ( enough for temp gauge but not consistent enough for fuel and oil pressure-both of those aftermarket items)
Click to expand...

Just a FYI I haven’t seen mentioned is the nuts on the back of the cluster can and do loose their contact due to age and basically tarnishing.

I have fixed a lot of gauge failures just by loosening and re tightening the nuts.
 
Mattax said:
In the illustration, the IVR gets power from the connection on the left.
View attachment 1716220336

When power is available, electrons move and we say current flows from the power supply to the ground.
Lets show the current from through the IFR.
Some electrons go through the resistance wire (heating element) to ground, and others continue to the gage and sender if they are connected.

View attachment 1716220341
Its the heating element that needs the ground. For the rally IVR this ground is on the back of the gage as seen in the other thread.

When the bimetal gets hot enough it breaks the connection.
View attachment 1716220346

Over time the input from the "12 volt system", really 14 V when running, results in output from the IVR that averages about 5 V over time.
View attachment 1716220344

My apologies if going over the IVR seems extraneous. The point is the ground at the IVR is for the heating coil, and each of the senders gets grounded to complete their circuits. So flow is like this.
View attachment 1716220354


from here Thermal-Electric Gauges (Session 227) from the Master Technician's Service Conference
Click to expand...
So as near as I can tell, my system is acting like all the components work but the sending unit is not grounded. I’m getting a pulsing current (5v) from IVR through the gauge into the connector on the sending unit. Except I checked the variable resistance on the brand new sending unit before installation and it functioned. I’ve also checked that sending unit is grounded to the frame.

The gas tank is new but it could be a hole in the float or the float arm stuck down? Maybe I can remove the sending unit, ground it to frame and manually adjust the float arm. That should at least tell me if it’s the sending unit or gauge end.
 
TrailBeast said:
Just a FYI I haven’t seen mentioned is the nuts on the back of the cluster can and do loose their contact due to age and basically tarnishing.

I have fixed a lot of gauge failures just by loosening and re tightening the nuts.
Click to expand...
I took steel wool and got rid of the tarnish and insured good connectivity throughout. That’s why I soldered the pins because one was not making contact.

1710207821363.jpeg
 
bacchustn said:
The gas tank is new but it could be a hole in the float or the float arm stuck down? Maybe I can remove the sending unit, ground it to frame and manually adjust the float arm. That should at least tell me if it’s the sending unit or gauge end.
Click to expand...
Set the multimeter to ohms. Measure the resistance from the sending unit connection to the fuel line (ground). It should be between 10 and 80 ohms. Check the oil pressure sender the same way. Just for sanity, do the temperature sender too.
 
A number of things come to mind...

As noted... If the temp gauge works the ivr works.

If you ground the wire at the fuel sender ( very short period of time) and the fuel gauge goes up the wire is good.

BUT....

If the L shaped connector has broken internal wires they might be making connection when you test BUT not when it is connected to the sender.

Also some senders have a nut on the threaded post and that nut can interfere with the connector going on all the way and making contact.

You can connect a jumper wire from the post on the sender to the sender L shaped connector to test if it's a connector issue at the sender.

For the oil pressure gauge...

If you grounded he sender wire at the sender and the gauge did not respond then there is an open somewhere along the path.

Follow it from the engine to the circuit board and see where touching a ground wire causes gauge movement.

If no gauge movement when shorting at the gauge then the gauge is most likely bad. Sometimes you can see a bad gauge by where the needle sits with the power turned off. If it sits well below 0 or the lowest tick that is an indication.
 
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