Fuel gauge issues

[ericwilkison]

I'm getting erratic readings from the stock fuel gauge and could use some help figuring out.

First some history: All the stock gauges were working good, well as good as the stock gauges work. I also had a cheap set of aftermarket gauges that were dripping oil on my leg. So I pulled them out removing a wye at the oil pressure sender, but otherwise not intentionally touching anything with the stock gauges. This is when my issues started, now the oil, temp, and fuel all maxed immediately and quickly on turning the key.

The gauge cluster needed a face lift any way, so I pulled it and took it apart for paint and check things out, roughly following the instructions at http://classicbroncos.com/speedoreset.shtml. All three gauges check out fine using the 9v battery test. But the voltage regulator did not pass inspection which I suspect was causing the gauges to max out. I ordered a new solid state regulator from Toms and put everything back together. I also installed new oil and temp sending units just to be sure. Now the oil and temp gauges work correctly again.

After all this the fuel gauge is very erratic. With a full tank it reads full. But when I get bellow 3/4 of a tank the gauge reads anywhere from E to 3/4 and is constantly moving. The swings roughly correspond to movement. Accelerating from a stop makes it go up. Stopping makes it go down. Sometimes it goes to E, sits there for a minute or two then gets to wagging back and forth again. The movement is not especially fast taking several seconds to reach the extremes.

Now, I'm trying to figure out if this is an issue with the fuel gauge or the sending unit in the tank. BTW, this bronco has only one tank, a 23 gal in the rear. Could the bad voltage regulator have fried one or both? Any suggestions and/or experience with these issues?

 

[DirtDonk]

Not sure if it could have damaged the senders, but being old senders (I assume?) it's just possible.
Or, as Broncos like to do with their owners, it's messing with you by throwing out "coincidental problems" just to keep you on your toes.

Sounds like the sending units to me, but with the new solid state regulator/reducer showing all the little oddities immediately.
I think (but don't know for sure) that one of the benefits/reasons for the original IVR's function of pulsing voltage signals was to not only work with the dampened gauges to keep readings stable, but to keep them stable during different temperature extremes.
So maybe the solid state setup is just showing you what is wrong with the sender more blatantly.

Just a guess though. Not really sure, but you could probably test the theory by yanking the plug on the tank sending units and jumpering the two wires together with a wire and resistor.
I don't think simply jumping them with straight wire (effectively grounding the unit with very little to no resistance) will help, because it already reads correct at full and doing that is only going to peg the gauge and keep it that way.
Not sure what value the resistor would be, but someone will.

Maybe it's just as easy, or easier even to test the sending unit with an ohm meter? Not sure.

Good luck though. Someone will have a good suggestion for you.

Paul

 

[ericwilkison]

I have a 23 gal tank that was installed by a PO. (I don't think that the 23 tank was available stock). Do they use the same sending unit as the 13 gal tank?

 

[Attac]

I have a 23 gal tank that was installed by a PO. (I don't think that the 23 tank was available stock). Do they use the same sending unit as the 13 gal tank?

Yes and no. Depending on who tank came from they can have a sensor that uses the same ohm range @ 10-73 for factory gauges. I have heard of some tanks that came with a different sending ohm range and the installer had to put some sort of adapter (help me out guys) to make it read correctly.
Run your tank until it's almost empty and take a ohm reading directly at sensor and then also at wire where it hooks to gauge. Then fill up and do the same again.
Also take your ground off rear crossmember where sensor grounds and clean it up real good and put some dielectric grease on it and reinstall.
As Paul said the new parts might be showing irregularities and funny enough when dealing anything electric, grounds are usually the culprit
Chuck

 

[DirtDonk]

Yeah, not the same. The factory was what the factory was. No optional sizes, just whether you wanted one tank only, or two.
The 23 gallon is aftermarket only, and the sending unit is aftermarket as well. Should be designed to work with the 73-10 range though, unless like Attac said there was a different one used and an adapter installed.
But that's pretty rare, as most companies have had correct Ford range senders for many years. People used to try to use GM based stuff that was more common, but hopefully that's not what yours is.

If you can find a decal or other indication of what brand the tank is, that will tell you what sending unit to use. We sell the ones for the old NWMP and now Sunset Metal tanks, as well as those for the Sherman and BCB tanks, and aux tanks as well.
They often start out as the same sending unit from the aftermarket, but are cut, tweaked and adjusted to work with a specific tank.

If you can't tell what you've got, post up a pic of it, or e-mail one to me and I can probably tell what it is.
But no, the factory sending units will NOT work. Not only the wrong size, but the wrong design completely. The only thing the same is the ohm range. Otherwise, physically they're nowhere close to each other.
The factory units will "fit" to each factory tank, but not correctly. You can use a main tank sender in an aux tank and it will work, but it's not aimed 100% correctly so using the proper one for each tank is the best practice. But neither will even fit into an aftermarket tank.

Here are at least some of the offerings I'm aware of: WH Fuel Tank Sending Units

You might even take a peek at the tanks on our site to see if any of them look like yours.
Back in the day there were many, but in the last twenty years or so there have mainly been three or four in various iterations.

Paul

 

[ericwilkison]

I just grabbed a few pictures the best I could. If you can identify the tank from this I'd appreciate it. I was not able to find a label, but as you can see the mud/gunk/sludge is thick on this one, could be one buried under there somewhere.


Looks like the sending unit is accessed through the top of the tank. I think I'll start by cleaning up ground and replace the old crimp connector with some solder and heat shrink.

The back of the tank:

This is the fuel supply line

The inlet and the two connectors in front of the filler tube go to the evap

 

[ericwilkison]

So, I just went out and cleaned up the wiring and the gauge is still erratic, I pulled out my voltage meter and started checking things. I connected the meter between the gauge output wire and ground. Couple minutes later I check the same place again and get a different reading by about 20 ohms, hmm. Noticed that any slight movement causes the resistance reading to start moving. Let it sit for 30 seconds and it settles down to a constant value. Push up on the frame rail to give it a shake and the meter starts moving again. Shake it a lot and I se it fluctuate up to 100 ohms. I'm thinking that the sending unit is shot and giving a bad signal. It should not be jumping around that much.

 

[DirtDonk]

Nope, good testing procedure. Showing a toasted sending unit. At least that seems the most obvious thing at this point.

No view of the side makes it a little harder, but the view of the way they did that "V" shield around the feed line makes it look like an old Northwest Metal Products tank. The same design we still sell, bought from them by a company called Sunset Metal Fabrication, but making the same basic tank.

So you can use a standard available universal sending unit with the Ford ohm range of approx. 73-10 (supposedly something like 73.4 to 9.8 or something odd like that, but we've been rounding off for 40 years) should get you there.
Our #9708 (WH/NWMP Fuel Gauge Sender is sized and adjusted for that tank already, if you prefer that way.

Of course, no matter what tank it's for, or who set it up, any sending unit (even stock ones for stock tanks) should be tested out of the tank, before assembling it inside.
This way you can verify that it's going to work with your particular gauge and wiring setup, as well as fitting into, and set up properly for your particular tank.
Especially since we're only 99.853% sure it's a NWMP tank.;D

Paul