Fuel gauge not working-again

[Ifitaintbroke]

This has been the most troublesome system on this truck. I've been trying to fix it for 4 years now with no success.

I'll start with where I am now.

I am running an Autometer fuel gauge. It uses a 12v signal. I did forsee any problems with that, but now am second guessing.

First, the front tank:
The front tank has worked fine ever since I put in a new sending unit 4 years ago. That is until about 2 months ago it started acting up. It would read sporadically and the reading was incorrect. Now it does not read at all.

I pulled the bed today (for the 4th time) and removed both sending units. The front unit is covered in white corrosion. The sending unit itself has a butn mark right in the center of the resistor bank. It's shows no continuity at any position, except when the float is pulled up as far as it will go. It then shows 16 ohms, which isn't even correct. It should be about 10 ohms. Here's what it looks like:







The rear tank:
The rear tank has given me trouble since day one. Long story short, it has never worked, except for once when I installed the current sending unit. It only worked for a matter of days, then the reading started to get lower until it didn't read at all. Recently however, it has started reading again. I pulled the unit today, and it is working flawlessly. 10 to 74.5, no problem. The tank is roughly 3/4 full, but the gauge reads 1/4. Obviously it is in the wiring. Some corrosion has developed somewhere. BTW, the rear unit has its own ground, about 12 inches long with a self-tapping screw in the frame.

Another problem: I fear my selector valve setup is not working correctly. Yep, the system that I talked so much about and spent so much time on! Here's the issue: the front tank is nearly empty, and the back tank is 3/4 full. Why that's a problem: I just put 5 gallons in the front tank, which was already 1/2 full. Thats roughly 15 gallons. Now, the truck has been driven about 2.1 miles since then, and it has idled in the yard quite a bit, but 15 gallons? Unfortunately, I don't know how much was in the rear tank, because the gauge hasn't been working. I fear the return valve is not working and the rear tank has been filling from the front tank. I'm very close to putting in manual valves.

[Ifitaintbroke]

Forgot to mention: I fear the 12v signal from the Autometer fuel gauge may have fried the front unit. Remember, the factory gauges were regulated down to 5v. I did not think this would be an issue, as the gauge reads by resistance, not voltage(to my thinking). But the gauge cannot directly sense the resistance of the sending unit, so the only way for it to know the level would be by a drop in voltage, right?

[mat in tn]

I'm assuming this is the 86 f250. the voltage is "regulated" to somewhat of 6-7 volts. if your gauge is being fed 12v therefore sending 12v by way of the sending units to ground then there may be an issue.

[Gary Lewis]

I think you've nailed it - placing 12v directly on the sending unit has burned it.

Is the original gauge bad?  I'd go back to the original gauge because you need the instrument cluster voltage regulator for the coolant temp and oil pressure gauges, so why not use it for the fuel gauge as well?  But, while you are in there I'd recommend replacing the ICVR with a true voltage regulator instead of the factory's chopper.

[Ifitaintbroke]

Good insight but it's too late for that solution now. My entire instrument cluster is aftermarket, and all 12v. I may have to make custom senders.

[Ifitaintbroke]

Here's what I might fo with: https://www.tanksinc.com/index.cfm/page/ptype=product/product_id=926/category_id=184/mode=prod/prd926.htm

It would require new holes in the tank but that's no big deal.

[viven44]

Supposedly the 1973 Bronco came with a 6 port manual valve. Those are unicorns. If I ever come across one.. man that would be cool.

Probably looked like this
https://www.amazon.com/dp/B00YMZ3YZM/?coliid=I2K7E4NJF0IPS6&colid=3IGQF00LDI4AO&psc=1&ref_=cm_sw_r_cp_ud_lstpd_41T6E65369DQB9Q9W4Y2


Else this would be what I would use next time
https://shop.broncograveyard.com/1966-1977-Ford-Bronco-Mechanical-Tank-Switching-Valve/productinfo/10260/

Jim talks highly about the Pollak valve. I will also definitely consider that..
but something about manual makes it sound dead reliable. Which it is. Since I went manual on big blue 2wd, it has been peace of mind.

[Ifitaintbroke]

Yeah I'm tired of band-aiding this system. As they say, "you can't fix stupid", and this is the dumbest system I've ever seen in my life. That manual valve looks tempting...

[viven44]

Took them only 25 years to get rid of the ridiculous dual tank approach and using 1 monster tank.

With that 38 gallon rear tank of yours, I would be mighty happy just having it. Even with the 460, thats over 300 miles range. Respectable.

[ArdWrknTrk]

I'm not sure where you expected Ford to put a single tank and a spare tire, but I like the fact that I have a completely separate 'reserve' tank if the other gets a hole (or pump goes bad) if you have electric in-tank pumps.

They boxed the frame by then. And all those frames rot in half like some damned Taco.

I've done away with the plastic 'nose cone' on my midship tank.
It only traps salt and muck, causing rot.

I'm sure 12v is causing arcing of the resistor board of the sender.
Have you considered 6v (ICVR) to the senders and using one of those, to make your cluster read correctly?  💡

My instrument won't read at all with the Meter Match, so I'm ready to eliminate it and go back to my needle moving up to 5/8 as empty.
Maybe we can make a deal?

[Ifitaintbroke]

Meter Match? Isn't that a sending unit "adapter".

[ArdWrknTrk]

Yes.
Gary has one to use '96 FDM's for his EFI 460 in an '85, and I've been trying (for 2 years!) to use '86 senders with an '87 cluster.
So, I'm about to get rid of it.

I have the manual, and the little screwdriver it comes with.
Look at their site. (I think they're like $70 now) but if you think it would work for your problem send me an email (click my username) and give me an address.

[85pig]

Early Broncos with dual tanks used a manual valve; a poster here put up a pic of his in another thread.  I had a 72 with one, and that setup inspired me to go manual valve on my 85.  I have the valve and a new rear tank, it's just a matter of having the time to pull the bed, re-plumb all of the lines, and install the valve.   I'm pretty sure you can get the Bronco ones from one of the Bronco parts places (Jeffs, Duffs, BC, etc.).  

Getting senders to work will be my only hurdle.  These threads help influence my decision.  Seems like the tank valves (and senders) are a chronic problem.  

[viven44]

Agreed that was a challenge on those trucks with having room for the spare tire, but

It was harder for me to drop and mount that spare tire with all that long rusty bolt/hardware... it was easier to drop even the fuel tank  I sure am glad they figured out a way to have a single fuel tank in later models and have a spare tire system an average man or woman could use.

[ArdWrknTrk]

85pig wrote

Early Broncos with dual tanks used a manual valve.
 Seems like the tank valves (and senders) are a chronic problem.

My personal experience is that my 6-port has never had a hiccup.
But obviously anyone reading these threads has a problem with theirs.

That's the ONLY reason I know Hot Fuel Handling (because other people have issues)
My truck is mechanical pump, but I enjoy problem solving and know I'm better with schematics than most, and memorize
part numbers, so I can be helpful....  

[viven44]

On mine, I just use a simple 3 way switch that ties into the fuel selector valve harness to switch manually between front and rear senders. When I manually switch the tank valves, I also switch the senders. "Works for Me!"

[viven44]

I had just about memorized this schematic in this thread below when I was solving my woes with the Ford factory fuel selector valve. After I realized that system had a chance to fail I could not trust it anymore.

https://www.ford-trucks.com/forums/1183355-84-ford-f250-w-460-and-dual-tank-issues-with-fuel-system.html

If that fuel selector valve was in the wrong internal position I saw the following problems
- if any of the fuel pump supply lines were blocked (happened to me), the pump would have a painful death over a small period of time
- if one tank overflows into another (happened to me), thats clearly an issue

I had drawn up an "FMEA" in my mind (an objective method to predict problems). Even though the 'occurrence' of these scenarios may be low, the 'severity' of all these scenarios was high i.e. being stranded on the road, dropping tanks (which I had already been through once). So I decided "Never again"

[ArdWrknTrk]

I congratulate you for including the mandated safety switches.  👍

[viven44]

I don't know if you are being sarcastic or for real. If sarcastic, can you please point on what safety is bypassed ? I do want to know. You have to dumb it down for me

As far as I know, all the safeties are still in place. Oil pressure switch, inertia switch.

[ArdWrknTrk]

I'm serious.
You have the impact (inertia) and oil pressure cut-off switches in your schematic.

I can't tell you how many morons would eliminate them. (I get to see the results of "die in a fire", it is something I never even want to think about)