69 roadrunner fuel guage

[19ROADRUNNER]

OK, have a 69 roadrunner that I can not get the fuel gauge to read right. I have the 5v to the gauges (temp works fine and so does the amp meter). the fuel gauge, full , reads about half tank. and drops fast as fuel is used. the sender is the aftermarket style, out of tank works perfect, 70ohm full and 9ohm empty. did plug sender in, grounded gender (all out of tank) and gauge works fine. . I have put an ohms box on the fuel sender wire to test gauge, and gauge works perfect, 70ohm full and 9 empty, but with the sender in tank fuel gauge does not work. have checked the ground to gauge and is less than 5 ohms. did try another after market sender , same problem. I am at my wits end over this guage and looking for help please. this is the last thing on my to do list for my friend that I have built car for (he is recovering from cancer and knee surgery) and would like to have a car like he drove back in the day. thanks in advance for any help given.

 

[69Bee]

Per the 69 Service manual:

Full should have LOW ohms, and empty should be HIGH ohms.

Float on empty stop = 72 ohms +/- 12 ohms
Float on full stop = 9.6 ohms +/- 1 ohm

 

[69Runner]

If I'm reading this right, when the tank is FULL then gauge reads 1/2? If so then you need to bend the float arm of the sender down.

 

[Dennis H]

Lots of talk on this. My 69 Coronet does the exact same thing. It did not work, does not work, and will never work. I take the mileage. New tank and sender. Wish I had the old unit to get it rebuilt. It worked fine.

 

[bigmanjbmopar]

Stainless steel tank? You said you have the ground strap on the fuel line and sender outlet pipe? Well good possibility the tank is too isolated from a real good ground, trying attaching a good ground strap to the tank or at a different spot on the sending unit.

I know this sounds stupid but sand the part of the sender pipe outlet some to get the stainless off and get to real metal. I think you are just not getting a decent ground, I had the same issue until I switched to 3/8" aluminum line and sanded the pipe some.

Sadly materials today are not as good as they were in 69'

 

[19ROADRUNNER]

sorry , you are correct that is how it is typed incorrect.

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the gauge reads correct with the sender out of the tank out of the tank, I wish it was that easy.

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yes soldered a wire from the tank strap (the clip from sender to fuel line) and attached to body of vehicle. I will try the sanding of the line. down to copper. I do have steel braded fuel lines, but even be for that I had the same concern,

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we think we have the original sender, and are looking for it. installed the 3/8 sender w/return for possible fuel injection, but did not do that at this time.

 

[anmracing]

If I'm reading this right, when the tank is FULL then gauge reads 1/2? If so then you need to bend the float arm of the sender down.

I agree with 69Runner, if it's working fine out of the tank, sounds like it needs to be adjusted. Let us know what you find out when you get it working right.

 

[19ROADRUNNER]

Per the 69 Service manual:

Full should have LOW ohms, and empty should be HIGH ohms.

Float on empty stop = 72 ohms +/- 12 ohms
Float on full stop = 9.6 ohms +/- 1 ohm

sorry , you are correct that is how it is typed incorrect.

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If I'm reading this right, when the tank is FULL then gauge reads 1/2? If so then you need to bend the float arm of the sender down.

the gauge reads correct with the sender out of the tank out of the tank, I wish it was that easy.

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Stainless steel tank? You said you have the ground strap on the fuel line and sender outlet pipe? Well good possibility the tank is too isolated from a real good ground, trying attaching a good ground strap to the tank or at a different spot on the sending unit.

I know this sounds stupid but sand the part of the sender pipe outlet some to get the stainless off and get to real metal. I think you are just not getting a decent ground, I had the same issue until I switched to 3/8" aluminum line and sanded the pipe some.

Sadly materials today are not as good as they were in 69'

yes soldered a wire from the tank strap (the clip from sender to fuel line) and attached to body of vehicle. I will try the sanding of the line. down to copper. I do have steel braded fuel lines, but even be for that I had the same concern

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Lots of talk on this. My 69 Coronet does the exact same thing. It did not work, does not work, and will never work. I take the mileage. New tank and sender. Wish I had the old unit to get it rebuilt. It worked fine.

we think we have the original sender, and are looking for it. installed the 3/8 sender w/return for possible fuel injection, but did not do that at this time.

 

[moparstuart]

yup bent the float down they are adapted GM senders and the arms set wrong for mopar tanks

 

[19ROADRUNNER]

yup bent the float down they are adapted GM senders and the arms set wrong for mopar tanks

I adjusted the sender full and empty before I installed in vehicle, 70ohms empty and 9ohms full. bent the stop tabs for arm travel.

 

[bigmanjbmopar]

Well, Again this may sound stupid but if all else fails and you want to give up, you can adjust the gauge itself. I have done it, it's very sensitive but the OE gauges do have adjusters on them to correct for any float inefficiencies. If you ever get your cluster out take a look at the gauge on the back there are little holes on the sides, look close you will see what looks like a gear or sprocket, one side for full otherside for empty, barely moving these up or down will adjust the needle position on the gauge to read where you want it to.





Here's what today's senders look like on the inside, they just ride on a contact point up against a wound coil (the whole thing is just a rheostat) This one had a small gap on it when it would get to the full side and would lose contact leaving the needle where it was on the gauge, bending the rod is one trick also bending the tabs on the top and bottom same thing but if that contact point stops touching anywhere inside it's over.

 

[19ROADRUNNER]

Well, Again this may sound stupid but if all else fails and you want to give up, you can adjust the gauge itself. I have done it, it's very sensitive but the OE gauges do have adjusters on them to correct for any float inefficiencies. If you ever get your cluster out take a look at the gauge on the back there are little holes on the sides, look close you will see what looks like a gear or sprocket, one side for full otherside for empty, barely moving these up or down will adjust the needle position on the gauge to read where you want it to.





Here's what today's senders look like on the inside, they just ride on a contact point up against a wound coil (the whole thing is just a rheostat) This one had a small gap on it when it would get to the full side and would lose contact leaving the needle where it was on the gauge, bending the rod is one trick also bending the tabs on the top and bottom same thing but if that contact point stops touching anywhere inside it's over.

yep, I did that before I reinstalled, took apart, cleaned, bench tested ohms, bent the tabs to 70ohms empty and 9ohms full, ran sender threw full sweep with ohms gauge on it looking for "open" spots. even after all that still read the same. replaced sender and still same thing. but gauge work perfect with an ohms box sending the ohms to gauge threw the sender wiper to gauge. just frustrating it is a simple wiring issue and can not fine it, been a autotech for 20years, this is tech 101.. lol

 

[bigmanjbmopar]

just out of curiosity did you bench test the sending unit with the gauge out of the cluster on the bench?

 

[69Runner]

I agree it's frustrating. It took me three or four attempts to get my replacement sender working on the 69. The replacements seem to drop slow from Full then plummet. That's probably why the Autometer replacement gauge for Mopar/Ford has a non-linear scale. Anyhow the first time I bent it the wrong way and got gas all over cause there was more in the tank than I thought. Eventually I had to hold the sender at the installed angle to visualize what was happening.

 

[Kern Dog]

I agree with 69Runner, if it's working fine out of the tank, sounds like it needs to be adjusted. Let us know what you find out when you get it working right.

This made no difference in my car, 1970 Charger with an aftermarket 3/8" sender. besides the float arm, I just recently noticed that there are 2 tabs on the sender body that limit up and down travel of the arm. They can be bent to allow a greater sweep of the arm. I'd think though that if the contacts in the rheostat don't touch after increasing the sweep, it would be pointless.

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I guess it might be a balancing act. The OHMs reading of 10 when full needs to be with the float resting against the top of the tank. You'd almost need a sacrificial gas tank to know for sure that the float is right there. Cut a hole in the top and install the sender, making sure there is enough range of travel for the float to touch. So many variables here though. I would imagine that with 10 senders, you could get 10 slightly different readings. They might all look similar but could have any degree of slight mis-alignment of the sender body, float arm/rheostat body, pickup tube...

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[19ROADRUNNER]

stainless steel tank? You said you have the ground strap on the fuel line and sender outlet pipe? Well good possibility the tank is too isolated from a real good ground, trying attaching a good ground strap to the tank or at a different spot on the sending unit.

I know this sounds stupid but sand the part of the sender pipe outlet some to get the stainless off and get to real metal. I think you are just not getting a decent ground, i had the same issue until i switched to 3/8" aluminum line and sanded the pipe some.

Sadly materials today are not as good as they were in 69'

i tryed the sanding of the fuel line on tne sender, looks like that helped the guage was reading empty, sanded to brass, reinstalled ground strap, the guage came up to about 1/4 tank, and that is what is about in the tank. Ill know more when i fill tank more, just did not have any fuel around house, and snow on ground. Thank

 

[wannadrag]

The Chinkish and Mexico senders are garbage,none read correct.Find a NOS or a good used original.

 

[19ROADRUNNER]

finally got gauge fixed, even tho the fuel gauge in car was working correctly with an ohm box installed. the gauge was bad... installed new gauge works perfect...... thanks for everyone that sent in their help...

 

[bigmanjbmopar]

out of curiousity, was the old gauge just off in its reading or just didn't move? I ask because these old gauges can be adjusted. o the back of them there are little wheels like cogs that set the range of full and empty by kicking up the cog gear up or down on each side.

 

[SlinktRR]

Hey bigman, if you adjust the wheels does it give you full gauge travel? For instance, if its reading half at full tank and empty at empty, if you adjust the needle to full will it register half when the tank is actually empty?