Fuel Gauge Acting Crazy

So I ran Gary's test over the weekend and have confirmed my Sending unit is bad.  Given that I installed a new sending unit 9 months ago, I will NOT use the same brand. As I don't want to do this again for a VERY long time, does anyone have brand recommendations? Thanks in advance for your thoughts!

Anyone ever use Spectrum?

I’m running Spectrum fuel deliver modules in Big Blue and they work well.

OK. I stayed away from them originally because they came with a plastic float and looked cheap. I opted for one that had a brass float thinking it was better. That's what I'll buy then. Thanks for the info.

If this is any help to anyone, I have found another possible ground problem. The top of the sender assembly has contacts going through it, and one of them is for the ground wire. It is possible, and I have seen it happen, for the "joint" between the sender assembly and this contact to corrode. If this happens, it will increase the resistance until your gauge no longer reads at all. This is what happened on my truck. When I found what the problem was, I took the sender out and cleaned it as best I could. The gauge worked fine for a short time, and then gradually read less and fuel in the tank, as it corroded again. I'm going to have to take it back out and try something else I've been planning for a while. More on that if it works. By the way, has anyone else installed the 38gal rear tank? If so, what did you do for the sender?

I am very annoyed by this. I, too, installed a brand new sending unit when I built my pump-on-a-stick and it immediately failed. I have a new unit sitting on the shelf that I was going to put in (which involves more than just dropping the tank and R&R of sender since I'm using a hydramat and custom pump for my ProFlo EFI). It does not make sense to me to go to the trouble of replacing it if there is a high likelihood that it will fail again. My wiring and gauge tested fine and I've got a ground strap on the tank; the sender is a piece of sh!t.

What is the problem here? Is there a flaw in the design of this part that causes them to be so prone to failure? Can some preventative action be taken besides simply testing before installation?

If there is no good as-stock replacement, what is the best workaround? Has anybody adapted another sending unit? Has anyone installed a separate aftermarket sender that worked well? Does anyone know if the sending units on the later trucks suffered the same problems as ours do?

Interesting.  And good question, Chad, if there is a way to prevent this.  Like soldering it.  Or adding anti-seize compound.  Or maybe dielectric grease.

As for later sending unit, I hate to jinx it but my fuel delivery modules are working well.  Some time after the Bullnose era Ford went to an integrated pump, sending unit, and control valve and called that an FDM.  I'm running them on Big Blue and have had no problems.

But, be aware that the resistance range for the senders is upside down and backwards to what the Bullnose gauges need.  So I'm running a MeterMatch unit to adapt them to the gauge.

And the external plumbing is different in that there's only a wye for the supply and a wye for the return.

Plus, you should have the later tanks as well since the FDM's have a tab that is in a different position than the tab for the Bullnose tanks.

So to make your fuel level sender dependable you have to replace your gas tank, fuel pump harness and sending unit and install an electronic device for your fuel gauge?

I'm not saying that you have to.  Just saying that's what I did and it seems to have worked.

Having said that, if you look at Ford's history of fuel systems they clearly didn't have a solid solution for many years.  They changed and changed and changed - surely because there were problems.

Even Factory Ford Fuel Senders for 1980-1984 were prone to fail in a similar fashion after awhile and/or read wonky in my experience.

If the aftermarket sector just copied them, then there you go...

mine seems to be taking heavy drugs and sleeping in. it can read dead empty and I can hit a bump. Then it sometimes decides to wake up. who can tell. I always fill the tank and always reset the trip meter just in case.
now my f250 with new tank and sender work great except not reading the range properly. I did not tune the float before install. it is something we should do but is it something that we should need to do? why get upset about it.

So, what about HOLLEY EASY LEVEL™ FUEL LEVEL SENDER?  It says, amoung other things:

Our all-new Holley Easy Level(TM) sender uses LiDAR technology to precisely measure the depth of fuel remaining in your tank and works with all Classic Instruments' fuel gauges, including short-sweep, full-sweep, and selectable ohm range fuel gauges. It also works with many other gauge brands. This model is compatible with tanks ranging from 4-to-39-inches. Setup is a breeze with the on-board buttons. Easily set empty and full tank positions, with reserve, right on your workbench before installing and then set the empty, half, and full positions on the gauge. The desired dampening rate is adjusted with dip switches right on the unit to reduce fuel slosh and gauge bounce by adjusting how fast or slow the gauge reacts to the fuel level change. Plus the necessary screws and gasket for installation are included.
 
Upgrade Classic Instruments' or other brands' gauge sets to capture the benefits of LiDAR, "laser imaging, detection, and ranging" technology. This exciting and innovative automotive application replaces vulnerable moving parts with a hi-tech laser; technology that has been used successfully in other applications for many years. An instruction sheet is included for Classic Instruments and other standard gauges. See additional instruction sheet below for AutoMeter applications.

Frickin' laser beams?

Seriously, though, it doesn't have any moving parts which makes it simple and elegant. At that price, it is the same as using a float style or a tube style or a reed style sender that do have moving parts and are built for specific depths.

I'd try it. I'm concerned that is says it doesn't work with ohm style readers (which is confusing because it implies it gives readings in ohms). I can get to the bottom of that one.

The other issue, though is that this needs to be installed on the top of the tank. That's the same problem with all of the separate sender units. This one is especially thick compared to others. I don't think there is any space above the tank, is there?

Good question, has anyone ever tried using an aftermarket sender? That's one of my next projects after this engine is built. (I never realized until starting an engine build how fast funds can disappear.)

well you did not exactly choose a cheap one either.

Darn right about that. I could probably build 5 small block chebbys for the same amount of money. But who wants a bunch of those pieces of junk laying around?

touche'

Littlebeefy wrote

Frickin' laser beams?

Seriously, though, it doesn't have any moving parts which makes it simple and elegant. At that price, it is the same as using a float style or a tube style or a reed style sender that do have moving parts and are built for specific depths.

I'd try it. I'm concerned that is says it doesn't work with ohm style readers (which is confusing because it implies it gives readings in ohms). I can get to the bottom of that one.

The other issue, though is that this needs to be installed on the top of the tank. That's the same problem with all of the separate sender units. This one is especially thick compared to others. I don't think there is any space above the tank, is there?

I'd be interested in this as well! Aside from your well thought out questions, wondering if this is direct bolt in for our tanks or would one have to cut a hole in the tank?  

Video on set up:

I know I'm the one that suggested the Holley unit, but now that I've had a chance to read up on it and look at the spec's I don't think this will work directly on a Bullnose truck.  But I think it can be made to work with those which only have a sending unit and not a pump in the tank, and MIGHT be adaptable to those with a pump.  Here are the issues I see:

Mounting: The Holley unit mounts with the "industry standard 5-bolt flange" with a 2.122" bolt circle. But our senders go in with a locking cam, not bolts.  So some kind of mounting flange would be needed that would use the locking cam and provide the 5-bolt mounting.  But I would think that could be done.

Pump: There doesn't appear to be a provision to have a pump occupy the same hole as the Holley sensor.  And the Holley doesn't appear to be sealed so that it can actually go into the tank, so I don't think it'll work if you also have a pump - unless you cut a hole and mount it separately.

Electrical: The spec's say the "Output is a PWM signal for 12 Volt applications (10 volts to 20 volts maximum)".  However, the guy in the video above keeps talking about a 0 - 90 ohm range, but if you listen to what he says he means that 0 ohms is Empty and 90 ohms is Full.  Our trucks use a 10 - 72 ohm range, but 10 is Full and 72 is empty.  So this won't work directly with a Bullnose truck.  However, you could add a MeterMatch between the Holley and the Bullnose gauge and it should work.  But that adds $90 to the total cost.

Bottom Line: Cool technology but not a bolt-in fit for a Bullnose truck.  Sorry.