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1952 Buick Special Fuel Sending Unit


HoboBuick
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Hey guys, just a quick, hopefully easy question for tonight.

 

I bench tested my fuel sending unit and it's all over the charts. I mean, way out, as in, in the mega ohm reading. No where near the 0-30 reading. So Im looking at going with the TANKS INC one.

 

My question stems from checking the connection in the trunk. I was always under the impression that there is no voltage going to the sending unit, since its just acting as a rheostat or variable resistor of sorts. With ignition on, and nothing connected to the socket in the trunk, my gauge reads full (as expected since there is basically infinite resistance), but when connecting the multimeter between the socket and the body/ground, Im getting around 2.7v. Is this correct? Just doesnt add up in my mind is all!

 

Any reassurance would be awesome. Thanks!

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I too just tested my Sending Unit for my '50 Special as I was in the process of cleaning the tank and installing a new fuel line.  My float was totally eaten away, but found an identical one off eBay.  I at first tried using an ohms meter on the Sender (tested out of the tank and disconnected from the fuel line and fuel gauge wire) and was also getting some wacky readings.  As you said, out of the 0-30 range AND not much of a difference when checking from Empty to Full.  However, I did a test as highlighted in the Shop Manual.  I took the Sending Unit up to the front of the car.  Removed the cowl access hole and attached a lead from the post on the sending unit to the left post on the back of the Fuel Gauge.  Next connect a lead from the mounting flange of the sender to a good ground on the car; I attached it to one of the dash brackets.  With leads that are a good 5'-6' you can then hold the Sending Unit inside the car with you.  Turn the Ignition to on, and try moving the float arm up and down.  On a '50, the needle on the Gas Gauge doesn't have all that much of a sweep, (I at first thought it was doing anything until I looked closer) as compared to the float arm swing distance.  I lucked out that when mine touched the stop at the top (Full), my gauge read Full.  When at the stop at the bottom, it was reading Empty.  A similar test can be done to check the front to rear wiring for the Gauge/Sender (IF it is already known that your Sender is working using the above test); steps below.

 

1.  With Ignition OFF disconnect Sending Unit wire.  Connect a lead from the post on the Sender (out of the tank) to the wire that exits out bottom of trunk..  Attach a lead to the flange of the Sender to a good ground on the car.

 

2.  Turn ignition ON, then move Sender arm up and down to the Full and Empty stops.  If wiring is okay, dash unit will move freely from Full to Empty.

 

3.  If, on the test, the dash unit reads Empty at all times or the reading is noticeably lower than from when testing the Sender directly connected to the Gauge, look for a ground in the wiring between the Gauge and the end of the wiring.  If the Gauge reads Full at all times or is reading higher than Empty or Full when at either stop, look for points of high resistance such as dirty connections, broken wire strands, or open circuits.

 

I know this is more of a manual process than just getting a simple ohms reading, but intuitively it should work (I'm not sure how "accurate" these gauges were to begin with as again on a '50 the Gauge needle sweep is only like 1/2" Empty to Full).  My next test will probably be doing the one I just highlighted in steps 1-3 above just to make sure that the Gauge reads Full or Empty when it's supposed to with the Sender still out of the tank, but attached to the wiring leading from the trunk.  I would hate to do this whole project, get everything buttoned up and come to find out I've got an issue with Sender to Gauge wiring.

 

Good luck.

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beerczar1976,

 

I appreciate the help with the explanation of the test. I already know my sending unit is faulty as I removed it and bench tested it without being hooked up to the car. Even if it were questionable, but working, it appears it has been repaired by someone soldering/brazing on the pick-up tube to the unit. For $40, a new one was a bit of an easy choice since it's out, and this will likely be by daily driver when it's done. 

 

I may have been unclear in my description of my question, but my question is about voltage. 

 

Should you be getting voltage at the lead connecting to the sending unit. I'm gettting around 2.7v. Are you supposed to be getting a voltage, or does this mean I have a chaffed or crossed wire?

 

~Anthony

Edited by HoboBuick (see edit history)
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I might be able to help - where is the connection in the trunk?  I replaced the tank & sender w/ new from Tanks, Inc. on my '51.  One issue is the new sender has a flared end to slip a hose over it - no thread.  So I had to cut the threaded fitting off the car-side fuel line and make a little jumper out of hose.  I then put an extra worm clamp on the tube on the sender side and another worm clamp on the frame-mounted tube with a jumper wire pinched under the worm clamps.  This is needed to provide ground to make the gauge work because the sender is electrically isolated from the tank because it sits on a rubber gasket, and I think the screws may have O-rings or some sort of non-conductive sealing washer under the heads.

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Awesome! The connection Im working with comes into the trunk on the drivers side, and come around towards the back. My car's trunk was a little 'mickey moused' so Im not sure if it's current location is where it's supposed to be. But it does come in on the drivers side. I think it's a white or natural colored with black parallel tracers.

 

And thanks for the idea of using the clamps. I was thinking of running a jumper from one of the screws that holds the sending unit in, but this might just make more sense...thanks! 

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Ok, took me a few days to remember to check this, but I got 1.9 - 1.91V on the tank level sender lead at the in-the-trunk joint in the wire.  Maybe the voltage you measure is correct, and maybe I was just working the probe through surface oxidation.  Anyway, I'd say it's not intended to be anywhere near 6V.  The gauge in my car works really well.

 

I add 5 gallons when the needle gets to the "G" in "G A S".  The needle on the gauge stops moving somewhere below the "G", but not at a definite, easily-remembered point (such as at the edge of a red mark or something), and the needle doesn't go all the way down to the "dot" below the "G" before the car runs out of gas...  I guess I could drive around with a couple-gallon emergency gas can in the trunk and try to find the engine-stops-here point again, but once was enough for me.

 

Once you get it working, consider anything at/below the "G" in gas as eminent-need-of-a-gas-stop, unless you drive with a (filled) emergency gas can in the trunk and figure out the actual out-of-gas point on the gauge...

 

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  • 2 weeks later...

Not to hijack this thread, but I have a '52 as well that came to me with the fuel gauge inoperable.  I dropped the tank the other day and found that the float was missing and that somebody had tried to make a sender flange gasket from Permatex (which explained why I'd have a gas leak when the tank was topped off).  So I popped a Caddy repro float on there because Bob's Automobilia and Cars, Inc. are fresh out of them, installed a gasket and swapped out the 5 old screws for new ones.  Upon re-installing the tank, the fuel gauge will work...in the ball park, anyhow.  Tank is about 3/4 full and it reads between a little over 1/2 and 3/4 full, depending on it's mood I suppose.  But when I start the engine the needle is flapping erratically between 3/4 and F.  Doesn't seem to follow RPM, just flicks at the right end of the scale back and forth as long as the engine is running.  Anybody got a diagnosis or an easy fix?  The insulated pad was still on the original sender and I did install it when I re-connected the wire to the terminal.

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You are welcome to pm me if it's easier, but my guess is to start by throwing a multi meter across the gage terminals. They are actually really easy to get to under the dash. One side will read 6 and change, the other around 2.7 volts. 

 

Do this with the car off, but key on, and again while running. Watch the meter to see if the voltage is fluctuating like the needle on the gage is. Just good place to start  

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