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Fuel gauge "reading" inaccurate - can I do this?

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CountryBumkin

Fuel gauge "reading" inaccurate - can I do this?

My fuel gauge is not reading empty accurately. I will run out of fuel when the gauge is still showing about 1/8 to 3/16 above the "E".

I've tried several times to get the sending unit float arm adjusted. I removed the tank, adjusted float arm and reinstalled. Would show empty before tank was actually empty. I lived with this for a while - I just made sure to fill up when/before the gauge read empty.

But now - I had to take the tank out to weld two bung fittings to it for my fuel injection install. Before reinstalling the tank,I bought a new sending unit. I set the tank on some saw horses and leveled it, and add about 2 gallons of water. Then I adjusted the float arm so I was reading 73 ohms on the sender terminals. I reinstalled the tank added fuel and the gauge is about 1/8 off (above "E" as stated in first line of this post).

It's a lot of work getting the tank out (plus I have a skid plate) - but it's not hard to get to the sender unit wires at the top of the tank.

So my idea is that, I could add a resistor (1 or 2 or 5 ohm, whatever it takes. I have an assortment). I would add enough resistance so the tank reads empty now (as I have just enough fuel in it now to be considered empty). I don't care if the "full reading" is off. The empty reading is what's important.

The sending unit/gauge specs say when the tank is empty the sender should be at 73 ohms and when full it should read 10 ohms. So I need to add some resistance to move the gauge reading "down" to show empty.

What do you think? Any considerations I may be overlooking doing this?

-Mike
1982 F250 4x4 XLT Lariat, 460cid, 9.5:1, TFS 290 Street Port heads, Crane Hyd. Roller cam (278/286 adv.,216/224 @.050, .560"/.586" lift), Edelbrock Performer 460 intake, MSD Atomic TBI fuel injection, MSD 6AL ignition, MSD Billet distrib., Hedman headers, NOS Cheater system, 4" Suspension lift, 3" body lift, 4.56 gearing, 17x12.5Rx37 tires MT Baja ATZ-P3.

Danny G

Re: Fuel gauge "reading" inaccurate - can I do this?

Is the tank level when its mounted to the truck?

I wish someone would make a capacitance based sending unit. No floats needed, it measures capacitance in picofarad's to give you a reading on volume. The truck could be upside down and still read.

1986 F-150|Standard Cab|4x2|300Six|C6Transmission w/3.08 rear|Name:TBD
2021 Ranger XLT Super Crew

Gary Lewis

Re: Fuel gauge "reading" inaccurate - can I do this?

Administrator

In reply to this post by CountryBumkin

That will work. However, you need a fairly high-wattage resistor as the current approaches one amp. I used 2 watt resistors in my calibration work and they got pretty warm.

So a 5 ohm resistor would need to be a 5 watt unit as at Full the equation is: Watts = Current x Current x Resistance. So 1 x 1 x 5 = 5.

Anyway, stick a resistor in and see what you think. Won’t hurt anything.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

Gary Lewis

Re: Fuel gauge "reading" inaccurate - can I do this?

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In reply to this post by Danny G

My Arduino plans could easily be altered to be used on a Bullnose sender as well as a later sender. And with the algorithm it would be easy to adjust it to make any situation work. Guess I need to make it happen sooner rather than later.

Gary, AKA "Gary fellow": Profile

CountryBumkin

Re: Fuel gauge "reading" inaccurate - can I do this?

Gave it a try - but the results are not what I expected.

I tried several resistors (1, 10, 12 ohm) until I got the fuel gauge needle to sit right at the "E" mark (actually just slightly above it) where I wanted it. It ended up being a 20 ohm resistor.

Then I added some fuel from my can, and went down to gas station and filled truck up. But it is only reading less than 1/2 full with a full tank now.

I was hoping I could move the needle up a fraction on the low side (empty reading) and the high side (full reading) with move an "equal amount".

I guess I need to go back and pull the tank and try to readjust the float.

---
The tank does not sit completely level (mid ship tank). The back of truck sits higher - but not by much.

What are the "Arduino" plans? Something to do with fuel sender/gauge accuracy?

Danny G

Re: Fuel gauge "reading" inaccurate - can I do this?

In reply to this post by Gary Lewis

In a capacitance set up could modify an existing sending unit with two full length probes for send and sense so it would be easy just to pop and swap.

For those who may be wonder what I am on about basically you are creating a system that is sensing electrical capacity of the fuel cell in the picofarad range. So we're talking 1 trillionth of a unit of capacity, very safe. So it doesn't matter where the fuel is in the tank, it will read the same so long as both probes have contact.

I have seen some retrofit probes for those wanting an in tank pump, maybe that's an option. Maybe be cheaper in the long run.

1986 F-150|Standard Cab|4x2|300Six|C6Transmission w/3.08 rear|Name:TBD
2021 Ranger XLT Super Crew

ArdWrknTrk

Re: Fuel gauge "reading" inaccurate - can I do this?

Administrator

Capacitance is an interesting idea!
Would it change with different blends of fuel?

Not sure why anyone would have to weld in TWO new bungs for an FI setup.
Just use the later tank, sender and pump.
Then Gary's backwards reading Arduino would make the gauge work.

My truck (being a one year wonder) has the opposite problem.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Fuel gauge "reading" inaccurate - can I do this?

Administrator

Yes, capacitance is a interesting approach!

As for the Arduino, it is explained in this thread: http://forum.garysgaragemahal.com/Bricknose-Sender-to-Bullnose-Gauge-Interface-td7174.html. And I plan to implement it as part of the EFI system for Big Blue as I’m going to use the later fuel delivery module that Jim described. Their beauty is in the fact that there’s no external pump or fuel tank selector valve as all of that is integrated with the FDM.

The downside is that their level senders work on a different resistance range than ours, hence the need for the Arduino to translate. But once the output, or Bullnose, side of the Arduino is figured out we can adapt the input side to about anything we want.

Gary, AKA "Gary fellow": Profile

CountryBumkin

Re: Fuel gauge "reading" inaccurate - can I do this?

In reply to this post by ArdWrknTrk

ArdWrknTrk wrote

Not sure why anyone would have to weld in TWO new bungs for an FI setup.
Just use the later tank, sender and pump.

Your suggesting buying a new fuel tank with a sender unit and in-tank fuel pump, rather than just weld in a bung at the bottom for the external fuel pump (that comes with the FI kit) and bung on the top for the fuel return? I suppose if I needed a new fuel tank, that would have been a good way to go.

Is the tank mounting/positioning and straps the same for the 19-gallon mid-ship (with carb engine) and the EFI setup? with the only difference being the size of the opening for the sender/pump unit?

Anyways, I went the re-using existing tank route. No problem with that - I'm just having a problem getting the sending unit float arm bent to the correct angle.

Gary Lewis

Re: Fuel gauge "reading" inaccurate - can I do this?

Administrator

I'm not Jim, but I think I know the answer. From 1985 on the tanks had the larger opening that allowed the fuel pump to go in. I'm going to use a 38 gallon Bronco tank with the later fuel delivery module and it appears to fit just fine - although I will have to lengthen the pickup and the float arm.

And the tanks up well into the 90's mount the same way, using the same strap arrangement.

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: Fuel gauge "reading" inaccurate - can I do this?

Administrator

In reply to this post by CountryBumkin

Yeah.
I'm sorry. I have no idea that your aftermarket fuel injection package comes with an external pump, bungs and a separate return line.

I think it's '85 and up that have a larger bung that fits the FDM, but I have a mechanical pump on the timing case.
So I have two contacts (sender only) but the later (16-160 ohm) sender instead of the 70-10 ohm sender of the hot spring type gauges.

Otherwise the tanks are the same.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

CountryBumkin

Re: Fuel gauge "reading" inaccurate - can I do this?

I think it's '85 and up that have a larger bung that fits the FDM, but I have a mechanical pump on the timing case.
So I have two contacts (sender only) but the later (16-160 ohm) sender instead of the 70-10 ohm sender of the hot spring type gauges.

Well that stinks. So the EFI fuel tank would fit but the sender unit wont work with the older dash gauge.

Using the original '82 tank requires two bungs to be added - and going with a EFI style tank would require some type of mod to the fuel sender unit. There is no simple solution - either tank style requires some sort of modification.

BTW, the MSD Atomic TBI kit I bought recommends that the fuel pump be installed "in the tank" - but says if that is not possible then mount it as low and close to the tank as possible. That is why I had the bung welded to the back/bottom of tank. I would have preferred an in-tank solution.

ArdWrknTrk

Re: Fuel gauge "reading" inaccurate - can I do this?

Administrator

'85 & '86 senders work fine!
I have an '87 cluster with reverse reading gauges but can't find a pair of '87 TWO POLE senders to save my life.

So I've got '85- '86 senders from LMC.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Fuel gauge "reading" inaccurate - can I do this?

Administrator

In reply to this post by CountryBumkin

There are several in-tank EFI fuel pumps that include senders that work with the Bullnose gauges. You can see them below from the Documentation/Fuel Systems/Fuel Systems Part Numbers/Senders & Pumps page.

But they usually require frame-mounted reservoirs and valves. Do you have two tanks?

Gary, AKA "Gary fellow": Profile

CountryBumkin

Re: Fuel gauge "reading" inaccurate - can I do this?

Just one tank. Mid-ship 19 gal. 133" WB

Which EFI tank works with the stock ('82) gauges?

Gary Lewis

Re: Fuel gauge "reading" inaccurate - can I do this?

Administrator

The '85 and later tanks have the larger opening and take the sender or sender/pump combo with the larger flange. Any sender or sender/pump combo for a Bullnose truck will work with a Bullnose gauge. Or did I misunderstand?

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: Fuel gauge "reading" inaccurate - can I do this?

Administrator

Exactly!

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

CountryBumkin

Re: Fuel gauge "reading" inaccurate - can I do this?

ArdWrknTrk wrote

I think it's '85 and up that have a larger bung that fits the FDM, but I have a mechanical pump on the timing case.
So I have two contacts (sender only) but the later (16-160 ohm) sender instead of the 70-10 ohm sender of the hot spring type gauges.

Otherwise the tanks are the same.

I thought this post was saying there where two types of sender units.

I removed the sender unit and tweaked it to read empty just as the fuel bung starts to run dry (even though there is still about 4 gallons in the tank).

I struggled to get the sender reinstalled. it was easy enough to get it out with one hand (using a brass drift and hammer to turn the lock ring), but I had a hell of a time trying get the lock ring reinstalled with one hand. I finally manged to get it in, but now I see the rubber sealing o-ring is sticking out on one side.

I'll need to drop the exhaust or driveshaft now to be able to get up in there with both hands and get this right.
Oh well.

ArdWrknTrk

Re: Fuel gauge "reading" inaccurate - can I do this?

Administrator

There are many types of sender units.
There are small bung (pre '85) units with two contacts.

There are large bung ('85-'86) units with two or four pins, depending on if you have a pump attached to the sender.
These units are low pressure and feed a reservoir, and a high pressure pump on the frame rail.

All of these read with the Bullnose gauges.

For '87--> you have large bung, but the sender reads a totally different scale, and it's reversed.
In '87 ONLY there was a two pin version for 351 HO and 460's with a mechanical pump on the engine.

At some point, the in-tank pump became high pressure and the frame pump/reservoir was eliminated.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

CountryBumkin

Re: Fuel gauge "reading" inaccurate - can I do this?

In reply to this post by CountryBumkin

CountryBumkin wrote

I struggled to get the sender reinstalled. it was easy enough to get it out with one hand (using a brass drift and hammer to turn the lock ring), but I had a hell of a time trying get the lock ring reinstalled with one hand. I finally manged to get it in, but now I see the rubber sealing o-ring is sticking out on one side.

I'll need to drop the exhaust or driveshaft now to be able to get up in there with both hands and get this right.
Oh well.

I complained that I had to drop the driveshaft to get both hands on the fuel gauge sender -- well, I was lucky I did.

Turns out I have a bad U-joint. I didn't hear or feel anything wrong - so if I didn't drop the shaft I would not have found out about the u-joint until it came apart somewhere inconvenient.

U-joint failure