Fuel gauge reading

I put a Dakota digital gauge in my truck, to clean everything up and in hopes fix improper readings from my old gauges. My fuel gauge still reads so off, and I am still guessing where my fuel level is. Is it simply as replacing the float in the gas tank? Or is the tank 100% welded shut, and I would have to get a New tank?

Sending units are removable.

Broncobowsher said:

Sending units are removable.

Click to expand...

I put in a fitech system, would that not have come with a sending unit?
Also, can I install a new one with the gas tank installed in the truck? Or is it easier to drain the tank and pull it?

Lastly, I’m going crawl under and check to see if it was replaced, but will this work with a 23gallon tank? https://www.cjponyparts.com/main-tank-fuel-sending-unit-5-16-bronco-1966-1969/p/FSU43/ or is this the proper one?
https://bcbroncos.com/shop/fuel/fue...it-23-gal-tank-5-screw-hole-for-early-bronco/
https://www.tomsbroncoparts.com/pro...unit-rearmain-23-gallon-66-77-ford-bronco-new

Sorry for all the questions! I’m still learning

Either of the last two should work for you. I like the second one from BC as it is customizable to your tank. You will have to drop your tank to do it also. And the Fitech doesn't come with a sending unit for tank. Ken

bronkenn said:

Either of the last two should work for you. I like the second one from BC as it is customizable to your tank. You will have to drop your tank to do it also. And the Fitech doesn't come with a sending unit for tank. Ken

Click to expand...

Thank you!

Stock tank you can remove the sending unit with the tank in the truck.
Aftermarket tank you typically need to drop the tank.

And though most are at least similar, you should know which tank you have installed to make sure you get the correct sending unit.
And if you have the time to mess with it, your old sender may be just find and simply needs some tweaking.

Did you buy the Bronco with the tank installed, or put the tank in after you owned the truck? Has the gauge read incorrectly all along? And how exactly does it read?
This info may help to determine if it's a bad sender (very possible) or just out of adjustment (also very possible).
And as many of us have found out, the aftermarket senders and aftermarket tanks don't always read correctly through the entire sweep (linear vs non-linear, etc.) but can at least read full and empty well enough to keep you from running out of gas.

Paul

DirtDonk said:

And though most are at least similar, you should know which tank you have installed to make sure you get the correct sending unit.
And if you have the time to mess with it, your old sender may be just find and simply needs some tweaking.

Did you buy the Bronco with the tank installed, or put the tank in after you owned the truck? Has the gauge read incorrectly all along? And how exactly does it read?
This info may help to determine if it's a bad sender (very possible) or just out of adjustment (also very possible).
And as many of us have found out, the aftermarket senders and aftermarket tanks don't always read correctly through the entire sweep (linear vs non-linear, etc.) but can at least read full and empty well enough to keep you from running out of gas.

Paul

Click to expand...

The tank was installed when I got the truck a few years ago. It will never read full it only goes to 3/4, and then slowly drops as I drive like normal, then will climb up and down periodically before suddenly going almost empty, then slowly climb back up then drop to empty until I fill it up again.

It was like that with the stock gauge and this gauge.

Yeah, erratic behavior like that is usually a loose wire or the sending unit. Most often the sending unit I think.

It happens. The not-quite-full reading could have been an adjustment, but the dropping, rising, then dropping again is something wrong.

As said, you'll have to drop the tank to access the sending unit. Unless the installer was very clever and added a door to the floor in the back like some do. Very handy that. But beyond most installers time limits.

Is your tank held on with bolts, or with a strap and J-bolt to the frame?
If a strap, then it's likely an older NWMP tank, or perhaps the newer version made by Sunset Metal Fab. Maybe in the last 10 years or so.
If it's held on with bolts through tracks welded to the sides of the tank, it's either a BC Broncos or Wild Horses Sherman tank.
If it's bolted to the frame with welded angle brackets then it's most likely an Aero Tank.
There are customs of course, and probably other production brands as well, but those are the main players in the larger Bronco tank category.
Most of the sending units start off similar, but are cut, tweaked and adjusted differently for different tanks. If you can't figure out what you have, then likely a universal sending unit with the Ford 73-10 ohm range style will be workable if you make sure it's adjusted properly for the tank.

Your old one can be tested once it's out of the tank, or maybe even a loose connection or wonky rheostat contact fixed. But likely you'll need a new one.

Good luck.

Paul

I had similar problems and am curious to hear the results of your findings.
I have a 23g BC tank that was installed by the previous owner, it read full when filled and then rapidly and steadily fell down to empty within a few days of driving. I would fill the tank and consistently it would be about 11 gallons in the tank when the needle was at empty. I purchased a new sending unit from BC (non-linear version I believe) and the results have improved by @1 gallons, now I have 10 gallons at empty. It doesn’t fluctuate or drop off suddenly, it’s just wrong. I was thinking that maybe swapping to a digital gauge would cure this? But it looks like maybe not?

Hinmaton


Sent from my iPhone using Tapatalk

Only if the digital gauge is programmable to specific ranges and variations within that range.
Which it might be for all I know. Best to check with the individual gauge manufacturer's instructions to see how they are set up.

But most likely you also have at least a partially misadjusted sending unit. Since it seems the sender's rheostat component is reading consistently, I would suspect that the arm is not being allowed to rotate through the entire tank before it comes up against it's stops.
In other words, the sender and gauge are talking to each other properly, but the range of the arm is limited to the top and middle of the tank instead of the top and bottom.

And after 44 years there are likely also to be slight variations between a gauge, it's wiring and factory specifications. The old 73.3 ohms to 9.6 ohms (or whatever the exact numbers are) range might give your gauge false readings. Add to that a float arm that is not running the full height of the tank and you get wonky readings.

When my '71 was five years old the gauge never read above 3/4 tank, and on empty it was quite a bit past the lower mark on the Empty end. It was exactly consistent between both tanks though, so at least it was consistent.
I bought new Motorcraft or Autolite sending units from the Ford dealer in about '79 or '80 and tested them outside the tanks. They read exactly the same as the originals.
So my gauge and wiring and the factory sending units did not match the expectations even back then.

I bent and tweaked the float arms and the stops on the senders until at full the gauge read a little more than a needle's width above the Full mark, and when empty (run bone dry) the needle was a tick below the Empty line. This worked perfect for me.
One thing I don't remember doing is figuring out how many gallons I had when the needle hit empty. Most cars have at least 3 gallons in reserve when the needle hits empty. Even new cars that give you warning lights, chimes, bells and whistles, and practically go apoplectic when you don't stop and fill up immediately, have 3 or 4 gallons left at that point.

I have suggested many times over the years that the sending units get sent in a separate box rather than installed in the tanks. At our place, each and ever sender gets tested to fall within the factory range. But that doesn't mean that after traveling across the country it's still going to be set up perfect for full and empty in the tank.

Sorry for the long story, but that's by way of saying you might even still be able to use your existing sending unit if you take it out and tweak it a bit. No way to tell without pulling it out unfortunately, but it's a possibility at least.
Next time you've got nothing better to do with the truck then%) see if you can mess around with it a bit.

Paul

DirtDonk said:

Yeah, erratic behavior like that is usually a loose wire or the sending unit. Most often the sending unit I think.

It happens. The not-quite-full reading could have been an adjustment, but the dropping, rising, then dropping again is something wrong.

As said, you'll have to drop the tank to access the sending unit. Unless the installer was very clever and added a door to the floor in the back like some do. Very handy that. But beyond most installers time limits.

Is your tank held on with bolts, or with a strap and J-bolt to the frame?
If a strap, then it's likely an older NWMP tank, or perhaps the newer version made by Sunset Metal Fab. Maybe in the last 10 years or so.
If it's held on with bolts through tracks welded to the sides of the tank, it's either a BC Broncos or Wild Horses Sherman tank.
If it's bolted to the frame with welded angle brackets then it's most likely an Aero Tank.
There are customs of course, and probably other production brands as well, but those are the main players in the larger Bronco tank category.
Most of the sending units start off similar, but are cut, tweaked and adjusted differently for different tanks. If you can't figure out what you have, then likely a universal sending unit with the Ford 73-10 ohm range style will be workable if you make sure it's adjusted properly for the tank.

Your old one can be tested once it's out of the tank, or maybe even a loose connection or wonky rheostat contact fixed. But likely you'll need a new one.

Good luck.

Paul

Click to expand...

Paul,

Since you seem to know everything there is about these trucks, From these pictures, would you assume this is a NWMP 23 gallon tank? I can get other pics if needed. I am going to replace my sending unit, and will this unit work for this tank? https://bcbroncos.com/shop/fuel/fue...it-23-gal-tank-5-screw-hole-for-early-bronco/ I figured if I am dropping my gas tank, might as well replace.

I have a centers wiring harness if that matters. Do I have a better choice of sending unit available for me? As well as I am running FiTech, not sure if any of that makes a difference. I also have the Dakota Digital Gauge https://www.wildhorses4x4.com/product/Digital_Dash/Dakota_Digital

I have never replaced a sending unit. I assume it works such as, emptying the tank, dropping the tank, pulling the old sending unit out, replacing with new one. (how do I set the new sending unit to the right settings?) connect new wires to harness, put tank back up and done? Or am I missing something?

Thank you!

mduenas said:

...Since you seem to know everything there is about these trucks...

Click to expand...

Hah! Got you fooled!;D

mduenas said:

From these pictures, would you assume this is a NWMP 23 gallon tank?

Click to expand...

Yes. Depending on how old it is, it's either the original NWMP, or the current Sunset Metal Fab tank. The strap retainer is the main clue, without anything to say otherwise.

mduenas said:

...and will this unit work for this tank? https://bcbroncos.com/shop/fuel/fue...it-23-gal-tank-5-screw-hole-for-early-bronco/

Click to expand...

I would not think so. It should be a different length main beam if I'm not mistaken. Check with BC before purchasing to make sure. They may have one with the proper sizing.
We offer the NWMP, or you can call Sunset Fab direct possibly.

Or you could go all exotic and get one of those tubular style that has no arm. But that might require more work than just slapping a new one in.
No matter what type you get, you should be testing it on the vehicle, before you install it in the tank.
We test all of ours to meet the Ford specs of (roughly) 70-10 ohms range. But as every vehicle's fuel gauge system might be different, it's best to confirm. You may have to make some adjustments to the float arm, the stops, or both.

Is it reading correctly now?

mduenas said:

I figured if I am dropping my gas tank, might as well replace.

Click to expand...

Absolutely!
Or at least test the old one. You don't want to have to do this multiple times if you can avoid it.
What's it doing now?

mduenas said:

I have a centers wiring harness if that matters.

Click to expand...

If you mean Centech, that should not matter. There is just the one sending wire and the one ground wire no matter what.

mduenas said:

Do I have a better choice of sending unit available for me?

Click to expand...

The correct style for the NWMP and proper Ford ohm range would be my first choice.
There are universal styles available that would probably be made to work, but 99% chance the one in there now is for a Ford. Assuming you had the tank before the Dakota Digital especially.

mduenas said:

As well as I am running FiTech, not sure if any of that makes a difference. I also have the Dakota Digital Gauge https://www.wildhorses4x4.com/product/Digital_Dash/Dakota_Digital

Click to expand...

Nope to the FiTech. Should not matter.
Nope again to the DD since it should be adjustable to suit just about any sending unit range on the market. But since it's likely already set up for the 70-10 Ford range, that's your best bet in sending units too.

mduenas said:

I have never replaced a sending unit. I assume it works such as, emptying the tank, dropping the tank, pulling the old sending unit out, replacing with new one.

Click to expand...

Yep, pretty much. Maybe someone will chime in with tips and tricks to make it easier, but you've got it in a nutshell.

mduenas said:

(how do I set the new sending unit to the right settings?) connect new wires to harness, put tank back up and done? Or am I missing something?

Click to expand...

Nope. Never just put one in the tank and hope for the best. Even the factory senders in the factory tanks did not read correctly right out of the box ever time. I bought mine directly from Ford and they read just like the (incorrectly) reading ones already in the truck.

Always test them outside the tank. Just connect it to the system, turn the key to RUN (don't leave it on after a quick test though, or you could run into trouble elsewhere) and run the sender through it's range while watching the gauge. A helper usually makes this much easier, but it can be done by one person in a pinch.

If it's not reading properly, you can tweak the stops and/or the float arm.
And it never hurts to test the float for leaks before you install it. I suppose water would work, even though it has different properties (specific gravity?) than gasoline. Maybe someone knows the answer to that one way or the other.

Before doing any of that, check any instructions included in case they want you to cut and adjust anything to length. The float arms usually are adjustable this way, but whoever you buy it from should have already done that I would think. We set them up for the tanks specifically. We just can't compensate for any variations electrically in your vehicle's wiring.

Hence the importance of out-of-the-tank testing.

Good luck.

Paul

I will let Paul answer the Q's about the sending unit and Dakota gauge set, but I will say this you will never get the stock gauge to read perfect at all levels with a liner sending unit, or even an aftermarket liner gauge and sending unit, the reason these OEM units are non-liner because of the design of the tank (the slope on the back of the tank is the cause of this). I did find a product that is suppose to allow you to calibrate a gauge to any ohm setting at a give position, I havn't tried it yet but will next time I have to change out the sending unit. Here it is
http://www.tanksinc.com/index.cfm/p...t_id=473/category_id=167/mode=prod/prd473.htm

I did talk them about the Fuel Link Gauge Interface Module and they said it should work just fine as long as I know the ohm reading at the given Full, 3/4, 1/2, 1/4, empty settings of the stock non-liner units. I think the full is 73 and empty is 10 but don't recall the others, I know they have been posted on here but havnt looked

DirtDonk said:

Hah! Got you fooled!;D



Yes. Depending on how old it is, it's either the original NWMP, or the current Sunset Metal Fab tank. The strap retainer is the main clue, without anything to say otherwise.



I would not think so. It should be a different length main beam if I'm not mistaken. Check with BC before purchasing to make sure. They may have one with the proper sizing.
We offer the NWMP, or you can call Sunset Fab direct possibly.

Or you could go all exotic and get one of those tubular style that has no arm. But that might require more work than just slapping a new one in.
No matter what type you get, you should be testing it on the vehicle, before you install it in the tank.
We test all of ours to meet the Ford specs of (roughly) 70-10 ohms range. But as every vehicle's fuel gauge system might be different, it's best to confirm. You may have to make some adjustments to the float arm, the stops, or both.

Is it reading correctly now?



Absolutely!
Or at least test the old one. You don't want to have to do this multiple times if you can avoid it.
What's it doing now?



If you mean Centech, that should not matter. There is just the one sending wire and the one ground wire no matter what.



The correct style for the NWMP and proper Ford ohm range would be my first choice.
There are universal styles available that would probably be made to work, but 99% chance the one in there now is for a Ford. Assuming you had the tank before the Dakota Digital especially.



Nope to the FiTech. Should not matter.
Nope again to the DD since it should be adjustable to suit just about any sending unit range on the market. But since it's likely already set up for the 70-10 Ford range, that's your best bet in sending units too.



Yep, pretty much. Maybe someone will chime in with tips and tricks to make it easier, but you've got it in a nutshell.



Nope. Never just put one in the tank and hope for the best. Even the factory senders in the factory tanks did not read correctly right out of the box ever time. I bought mine directly from Ford and they read just like the (incorrectly) reading ones already in the truck.

Always test them outside the tank. Just connect it to the system, turn the key to RUN (don't leave it on after a quick test though, or you could run into trouble elsewhere) and run the sender through it's range while watching the gauge. A helper usually makes this much easier, but it can be done by one person in a pinch.

If it's not reading properly, you can tweak the stops and/or the float arm.
And it never hurts to test the float for leaks before you install it. I suppose water would work, even though it has different properties (specific gravity?) than gasoline. Maybe someone knows the answer to that one way or the other.

Before doing any of that, check any instructions included in case they want you to cut and adjust anything to length. The float arms usually are adjustable this way, but whoever you buy it from should have already done that I would think. We set them up for the tanks specifically. We just can't compensate for any variations electrically in your vehicle's wiring.

Hence the importance of out-of-the-tank testing.

Good luck.

Paul

Click to expand...

Thank you for all the info, I for some reason had missed you had one for that tank!

Last and assuming a very silly questions, The previous owner told me it was a 23 gallon tank, I just saw on your site there is a 20 gallon option. How can I tell what size it is, before I order the unit.
I have ever at most put 19 gallons in the tank.

The one in the tank now reads all over the place, and at most with the dakota digital reds 86% full, then drops and rises sporadically.

Sounds like a bad sender then. Or a loose connection somewhere.
Do you by any chance have two tanks and a dash switch for the gauge? If so, check that first. Very often they fail slowly and give funky readings before just letting go completely.

Easy to tell on the tank too. The full 23 gallon version has a "bump-out" towards the front of the truck that sits under the rear crossmember. The 20 gallon tank was specifically for trucks with body lifts, so they removed that additional space to allow the tank to move upward without hitting the crossmember.

Make sense? If not, shoot another picture at the fuel outlet and post it up.

Paul

Do I need a lock ring tool for the NWMP tank sending unit? Want to make sure I have all this before pulling it down. I ordered the wild horses sending unit, anything else I need?

Lock ring tool

Hah! Good one Ken.
To that mduenas, nope. On the tanks like this they're all either screwed or bolted down. So the "special tool" model in bronkenn's photo, or a small socket are all you need.
You'll have to see what was used on yours once you pull it down far enough to check out.

There are probably more and more aftermarket tanks utilizing the factory style locking ring, but they generally have not trickled down to the Early Bronco applications yet.

Paul