Fuel Gauge Issue

[swisswill]

I need some help with my fuel gauge and I'm hoping someone here can point to something I've overlooked. !976 Dart that didn't have a functioning fuel gauge when I bought it. Had zero resistance, pulled the sender and the float wasn't floating. Installed new sender, still nothing so replaced the voltage regulator with the RT Engineering unit and the gauge works. Fast forward to my Sniper 2 install using Holley's in tank pump and it works, but reading less fuel than reality, I'm okay with that. All of a sudden the gauge stops working. Ultimately I warranty the pump because it's VERY loud and Holley figured the pump was bad. Install new pump, add fuel back to tank (car on jack), fuel gauge needle moves, thought I was good. Drop the car down, go for drive a few hours later, no fuel level on the gauge. I have done everything I can think of to diagnose the issue and I'm stumped. Below is a summary of what I've done thus far.

• Ground the gauge to the battery, needle moves.
• Ground the gauge to the same ground the sender is wired to, needle moves.
• Measured resistance at the Holley connector, both sides, 39.2 Ohms.
• Measured resistance at the connector on the back of the cluster, connector unplugged, 39.2 ohms.
• Plugged connector in ~1/2 way, just enough to get a probe on the circuit board stud, 0 ohms.
• Plugged connector all the way in, 0 ohms on the gauge stud, 0 ohms on the circuit board.
• I have a second circuit board (not from a 76), plugged in the VR, added a second fuel gauge, ground the circuit board to the battery, 0 ohms at the gauge, but 39.2 at the plug when plugged in.
• Wired old fuel sender directly to the gauge, gauge needle moves when I move the float by hand.
• Wired old Holley fuel sender directly to the gauge, gauge needle moves with the float.
• I have continuity from the trunk connector to the connector at the dash.
• I have continuity from the circuit board stud to the gauge stud.
• Do not have continuity from the trunk connector to the gauge stud.

What am I missing? Everything else on the cluster works, except the right blinker but that stud is broken off the circuit board. Any thoughts on what I can do/test next? Thanks in advance.

 

[eekvonzipper]

I do apologize... I couldn't resist.

 

[swisswill]

See, I knew there was something I was missing.

 

[Dana67Dart]

There might be more truth to that!

If the resistance range of the Holley sender is such that it does not provide:

10 ohms full
23 ohms 1/2 tank
73 ohms empty

Note 23 is not 1/2 of 63.

The sender provides a curve to the gauge.

That being said if your sender is providing 50 to 80 ohms due to the fuel level in the tank it could be reading empty.

As for being 0 ohms (dead short) maybe you are pinching the sender wire under certain conditions.

 

[eekvonzipper]

Mine drops quickly to Empty (maybe 6 gallons) with a Newer sender...
irritating, but the upside is a $20 dollar fill-up!

 

[swisswill]

There might be more truth to that!

If the resistance range of the Holley sender is such that it does not provide:

10 ohms full
23 ohms 1/2 tank
73 ohms empty

Note 23 is not 1/2 of 63.

The sender provides a curve to the gauge.

That being said if your sender is providing 50 to 80 ohms due to the fuel level in the tank it could be reading empty.

As for being 0 ohms (dead short) maybe you are pinching the sender wire under certain conditions.

I checked the original Holley sender and it wasn’t perfectly 10-73 but it was close to it. I figure at 39 ohms I should have slightly more than 1/2 tank. I’ve played with grounds but haven’t run a ground direct to the battery. Instructions don’t call for it but I might as well test it. I currently have it grounded to the same bolt the taillights are grounded to so I figure that should be sufficient. But with resistance to the cluster connector, I figured I was good.

I’ll have to look to see about pinched wiring. I may run a test wire to the gauge itself and see where that puts me.

 

[Dana67Dart]

. I figure at 39 ohms I should have slightly more than 1/2 tank

39 is going to be closer to 1/4 tank

Look at the ohms to gallons chart.

The gauge needs a curve but most aftermarket senders do not provide a curve so it is off from that too

The tank is not rectangular the top has the cutout for the spare, so the first 5 gallons go down fast, the next 6 to 8 go pretty liner, then the tank is sloped so the last 5 or so go quicker but not as quick as the top 5

Product Review: A100 Fuel Sender For 67 Dart

 

[swisswill]

That’s interesting, thanks fo sharing that @Dana67Dart . I’m going to pull the sender and check the resistance throughout the arms movement. Since it’s an electric pump I can pump out what’s in it and compare that as well to what the gauge should read when I put it back in. I pretty sure I still have an issue because I have fuel in the tank and I’m not marking anything on the gauge, but I don’t know how much fuel. Thanks again.

 

[Dana67Dart]

What I did was drain out all the fuel

Then add back one gallon at a time and take ohm readings.

Keep in mind that there is so e additional resistance in the wire from the sender to the gauge. So to get the best readings measure at the wire closest to the gauge.

The inner kick panel on the drivers side has a connector you can disconnect and measure there.

Lastly 1/2 the senders range will not represent 9 gallons in an 18 gallon tank. (tank shape)

 

[69conv]

My car has a grounding strap from the sender at the tank to the fuel line on the other side of the rubber hose at the tank. If it becomes corroded the sender malfunctions.

 

[swisswill]

My car has a grounding strap from the sender at the tank to the fuel line on the other side of the rubber hose at the tank. If it becomes corroded the sender malfunctions.

I didn’t have a strap on the original but did have a copper wire going from the fuel line on the sender to an exhaust bracket. I have added another copper line from the same spot on the new pump/sender to another grounding location and no change. Tested the ground by grounding the signal wire to the copper line and the needle moved so that ground wire is good. Did the same to the ground location for the sending unit ground wire and same thing.

@Dana67Dart I drained the tank and pulled the sender, I see exactly what you mean about range and resistance. I pulled roughly eight gallons out and the gauge was reading empty. Hooking up the meter, at 40 ohms it’s empty, but has 8 gallons of fuel. This sender is terrible. I also do believe I have an issue with the factory wire, connector or circuit board. Based on testing today.

 

[Dana67Dart]

@Dana67Dart I drained the tank and pulled the sender, I see exactly what you mean about range and resistance. I pulled roughly eight gallons out and the gauge was reading empty. Hooking up the meter, at 40 ohms it’s empty, but has 8 gallons of fuel. This sender is terrible. I also do believe I have an issue with the factory wire, connector or circuit board. Based on testing today

There is a devise called a meter match.

Many have had good success with it

Basically set empty, 1/4, 1/2, 3/4 and full.

And it provides a conversion from what the sender is providing and what the gauge is needing

 

[swisswill]

There is a devise called a meter match.

Many have had good success with it

Basically set empty, 1/4, 1/2, 3/4 and full.

And it provides a conversion from what the sender is providing and what the gauge is needing

I'm going to look into the Meter Match. Looks like it's made by Tanks Inc, maybe others, which is funny because my next move was a new tank, sender, and pump from Tanks Inc using one of their reed switch senders. Who knows, maybe I'd still need the meter match. Thanks for that tip @Dana67Dart.

Here's the rest of the story on my fuel gauge. After fussing with grounds to make sure my ground was still good, I started messing with the sender wire. I went directly from the sender to the gauge and I had full range of motion on the gauge, albeit the ohms didn't match up, ~39 empty, 10 full, 24 half full, and 27.5 1/3 full. I pulled the cluster out and looked closer at the pins for the connector and found the fuel gauge pin very loose. I soldered it, and another, and have a functioning fuel gauge using the factory wire. Then I put it all back together, put my 8 gallons of fuel back in and still no needle movement, but I only have 39 ohms which = empty apparently. So meter match it probably is for me, and perhaps a new circuit because I am missing a pin still. Thanks again.