The Stovebolt Site Forums The Shop Area The Electrical Bay New sending unit issues

Yes, a string attached to the float arm and threaded through one of the 5 holes. I've done this before and while it is crude it will allow you to be certain the float is rising. Sounds like the float is okay. Sorry Bartamos...I thought he said cork and rubber floats. My error.

One of the reasons I wanted you to check with the multimeter to know if your ground was good was to make certain you had the two wires positioned correctly (I suspect you do). On most multimeters there is a buzz sound you can use to see if you have a solid circuit. Disconnect the green wire, connect it to one of the multimeter leads, find the little buzz selection, connect the other lead to a known good ground spot and see if you hear the buzzer. Or if your meter doesn't have this function, the resistance should go close to 0 when you touch the other lead to ground.

[quote=Forget it

Jon,
My guess is float bad or float arm sticking. That's what logic says but logic is just an educated guess. Unless there a some factor not disclosed yet. Mistaken info.

Please see the attached images. Something else dawned on me as a possibility. I'll do my best to describe it. In the first image you see the top plate of an OEM 1952 pickup sending unit. It might look like you can mount this 5 point star in different ways but you can't...or that is to say it should be made so the bottom two points of the star (across from the one closest to the sending wire connection) are slightly further apart. This forces the float rod to swing parallel to the tank sides, however (a large however) if you install the float backwards...that is pointing toward the outside wall of the tank and not toward the center of the tank...the float can rub on the side of the tank and keep it from working. The second float orientation image in the attached images are not what you want your float to look like. You want it to look like the first image...pointing to the interior of the tank.

Jon,
Of all the senders I have worked with, the hole pattern is "keyed" so it only goes on one way. I already mentioned that I didn't undertand how he could try it two ways. I posted my guess just before you posted. Are you saying that the senders arrive and need assembly?...and can be assembled backwards?
FYI: we never go the Summit part number. I searched the Summit site yesterday for 1950 fuel sender and got 2000 hits.

The spacing of the holes prevents the top plate from being mounted incorrectly. However on a couple of the generic replacement senders the beam (the beam that holds the sending unit) is capable of being attached in 4 separate orientations. The original sender was a stamped little rectangle (you can see it in my image) but some of the generic replacements aren't...the stamped recess is square and that means the float rod might be trying to operate 90 degrees out of the intended spot. Somewhere I kept one that came to me that way.

Good info Jon
Poster says "it is correct for year and model". This does not indicate a generic I guess.

Summit is not on my list for a part like that.

I suggest to others to use venders who specialize in our trucks, not a drop shipper with parts for vehicles up to 2023.

And there it is. Chinese special. The mast can be mounted in any of 4 positions and as you can see this one is mounted 90 degrees rotated from what the AD tank will need so it could never work the way it was assembled when I got it.

Good work Jon.

Jon
Thank you taking the time to help me.
I just want to give you more information.
So I topped off the tank to roughly 3/4 inch from the top.
I re-installed sending unit hooking up only the ground ohm meter register 27. Good right?
But then I hook up signal (red wire) and it drops to 10.
Gauge in instrument cluster measures a little less than 3/4 full.

Perfectly understandable when you realize that you're measuring the resistance across the sender AND the gauge coil in parallel.

The only way that you get a true reading of 0-30 0hms from the sender is with it isolated from everything but the meter.

If your tank is 3/4 full and the gauge reads 3/4, then what are you worrying about?

Ment to say 3/4 of an inch from top sorry

Hi Cheap,
As Kevin said isolate the sender...remove one wire (ground or signal wire, doesn't matter) and then connect the tester again. With both wires connected, you have the resistance of the fuel gauge in play plus the resistance of the wires themselves...but we are making progress.

By the way, yes...27 ohms is good. That should provide an almost full reading on your gauge...presuming the gauge is working okay.

This is good reading as my mechanic friend is going through the same thing now. Fuel gauge is original and never removed from cluster., all other gauges work. New tank and sending unit, the old one was a rusted cruded up mess. Original wiring, sender is oriented in the correct direction, float floats in a bucket of water( never had fuel in the float) I have about 10 gallons of fuel in tank, gauge reads empty. Remove the center wire from sender and gauge goes to full. Sending unit out of tank with gauge wire attached to center stud and then ground the flange to tank, move float up and fuel gauge reads E to F as it is raised up. Sending unit back in tank and ran ground wire to neg on battery, still reads empty. Same problem as original poster. The 5 screws holding the fuel sender flange to the tank are new, old ones were still clutch head screws. I don't remember where I bought the sending unit, as it has been a few years when I was buying parts for a truck that had sat for 31 years, my fault. It would have come from a vender selling parts for these AD trucks. Will keep at it and get it solved, your replies have helped to try some things. 1950 3100 that is very original, just neglected from sitting for 31 years. It does start easily and runs good now.

Jon
Please explain what I will be looking for when I remove 1 wire.
Do I test with key on or off
What should the fuel gauge and multimeter read when testing.
Sorry to keep bugging you but like you stated we are making progress.
Is it possible if everything checks out its a bad gas gauge, if so is there a way to test it while still installed in cluster in the dash?

Yes. It involves three 15 ohm resistors, some wire and soldering skills.

Hi Cheap,
You need to remove one wire at the sender (either one is fine) and then use your handheld gauge to check the resistance...key off. Your tank is full or very near it, so I would imagine your resistance ought to be in the high 20s or approaching 30 ohms.

To test your gauge in the dash, the easiest way is by disconnecting the signal wire from the sender at the tank (the red one in your case), connecting a 33 ohm common resistor to the signal wire's connector (you can just hold it with your finger and thumb) and touching the other end of the resistor's lead to a known good ground spot...ignition on. That should cause your fuel gauge to jump to full because the + contact of your gauge will see a ground connection, but it will be restricted to 33 ohms. If you need a 33 ohm resistor, please send me a PM with your name & address or send an email to jon_goodman@yahoo.com
I think I have a few around here and will be happy to send one. I probably also have a 15 ohm resistor, and by doing the same test with it, your gauge should register around half full. That should be a good test for the gauge.

Wouldn't you just connect the resistors across the gauge terminal and ground? A 15 ohm should make the gauge go to about mid scale, a 30 ohm should indicate full, and shorting the terminal to ground should show empty. Aren't you just simulating the sender?
[on edit] Looks like Jon gave a better and more complete explanation than I did.

For what it may or may not be worth, the way direct current electricity works is simply this: all the electrons want to go home right now. It is what they exist for, actually. In a system which has negative ground "home" is ground and all the + electrons want to go there. Management of those electrons to make them do just what we want them to is the trick. Some of them may run a clock, some may run a radio, others may illuminate headlights and other lights, some may heat up a cigarette lighter or run a heater fan. They might be directed to a USB port where they'll charge your phone. And it is all about the positive guys (+) wanting to make it to the negative side (-). Alternating current electricity is different, but you don't have any of that in your pickup. If you want a nice book on the basics of electricity, download this:

https://www.zpag.net/Electroniques/Kit/Getting_Started_in_Electronics_-_3ed_-_[Forrest_M.Mims].pdf

It is easier, Kevin to just use the signal wire (assuming it goes to the gauge in good shape...which our OP has said he checked). Here's why I say that:
The coil on the left of the fuel gauge is referred to as the choke coil and the other (on the right side of the gauge) is the operating coil. When you turn on your ignition, current runs from your battery through the choke coil and also over to the operating coil via the common connection between the two coils. Once it arrives at the operating coil, some current runs right through and to ground. This energizes the choke coil and the operating coil to an extent. Some more current at that junction runs back to your fuel tank and through the variable resistor that is your sending unit. And here is where the magic takes place. If you recall, this sending unit will register 30 ohms of resistance when your tank is full and 0 ohms of resistance when your tank is empty. When there is less resistance, more current will flow through the choke coil and the choke magnet will be stronger, pulling the needle to E. When there is more resistance, then more current is pushed into the operating coil and then this coil's pull will overpower the choke coil, pulling the needle toward F. And since the resistance is variable, varying degrees of resistance will cause more or less current to be in that operating coil and the needle will be pulled more or less toward F (or toward E) proportionally. So by connecting common resistors between the signal wire at the sender and ground, we'll simulate a working sender...in my suggested case with half full and a bit more than completely full.

TMI, Jon.

[on edit] How about writing up a tech tip on our gas gauges?
[on edit - again] You already collaborated on one. (I should have known ) It's here: Tech Tip on Troubleshooting gas gauges

Hi Kevin,
I've done that...actually have written up one on installing the sender correctly and another on "How Your Fuel Gauge Works...sort of" which is just a cleaned-up version of a report I wrote here maybe 3 years ago. It has images and other things that hopefully will de-mystify the fuel gauge and how/why it works. Around the same time...maybe 4 years back...I was working to create a fail-proof and very long-lasting sending unit for the AD fuel tank. And I did. I created a walloping and very accurate sender but there's one out there for $29 delivered that is just as good and created by a gentleman in Taiwan who has his ducks all in a row. I can't make the sender I devised for $29. Peggy, Phil, John and maybe others (as I'm sure you know) are working on revising the tech tips now and hopefully it will be part of that group.

Yes! That's Phil's work...he did it and I just sort of looked over his shoulder a time or two.

Yes, three 15 ohm resistors simulating the sender at empty, 1/4, 1/2, 3/4 and full.
A 10 pack of 15 ohm resistors can be had for under $5 on Amazon.


With the key on the first test is does the gauge read full or more when the sense wire is removed from the sending unit and empty or less when the sense wire is touched to ground?

If no to either, the wire or the gauge is bad or the gauge isn't getting voltage from the battery. No sense going further until that problem is fixed.

If yes to both the wire is good and the gauge is working somewhat, so continue testing. Work the image below from left to right and you only need 3 resistors.

Cool! Thanks for posting that figure, Bill.

Jon, I recall your posts on that bulletproof sending unit.

I thought it was a noble idea, Kevin. Flat wound Kanthal wire, stainless steel and brass with a stainless steel ball to measure the resistance. Smooth and accurate but there was the cost issue and with many vote with their wallet. A couple of images of the prototype I made attached.

Why is the focus on electrical if it all works in semi bench test mode? That has been asked and I did not see an answer.
I think if a wheel bearing was loose, Jon would put a multimeter on it.
This is going off the deep electrical mish mosh end for no reason. According to the poster the electrical wiring and ground is the SAME in both test modes.
Hello? Earth calling. Come in Sparkies.
'

Your multimeter doesn't have the wheel bearing function, Bartamos? Here...take a look at mine...

Okay...everyone can get back on topic and try to figure out what is the matter with Mr. Cheap's sender, gauge or whatever.

I would like to know how much force is required to manually move the arm on this particular sending unit. If the force required to move the arm exceeds the amount of force imparted by the the buoyancy of the float, why, you got a hitch in your gitalong.
(Please excuse my cowboy ranch terminology. There is an Arizona rancher a listening in. I reckon anyways.)

I was having the same problem with my fuel sending unit from Classic Chevy Truck parts. It would work outside the tank holding the wires to it, moving the float arm up the gauge went from E to F. Full was 30 ohms. Put it back in and it would not move off of empty. Remove signal center wire and would go to full. Just would not work in the tank. I ordered a new on and it checked good, 0 to 30 ohms and E to F by raising the float arm, just like the old one. My mechanic would not give up, must have removed it 15 times. Finally figured out that the center wire stud was making intermittent contact. He could wiggle it and the needle would defect up to full and back down. Never did figure out what caused it. Put the new same style sending unit and it works perfect.