Jeff, or anyone, I can't find the fuel sending unit thread s

[rock]

Hi Jeff,and all,

After 25 years of not worrying about a non functional fuel level gage I did a complete truck rewire with relays for most functions, and added in new Auto Meter gages, including a 2 5/8 inch Phantom for the fuel level. Course the new gage didn't show any more action than the previous original so my hope it was the gage was crashed. SO I measured resistance from tank fuel sender stud to ground with tank full and then empty. It was 40.6 ohms each time. I ran a new good tank ground and re tested resistance with same results. Seems pretty clear that the sender is bad. I know how to get it out but want to see if there is any more testing I can do to the sending unit in place before pulling it. And I could sure use a part number or want to buy a used sending unit if this is bad. This is a wedge shape tank behind the sea, holds about 15 gallons, the tank and sender are OEM as came in the truck.

Thanks!
rock
'64d100

[wideblock]

finding a good used on is your only hope. i havent seen anyone offering new sending units for these tanks. sounds like you did all the needed tests. to me it sounds as if your float is sunk. try pulling the sender and make sure everything is clean and the arm is moving freely. a lot of times if the truck sat for years, it will rust in one position. also, on the sender in my truck, there is a very small ground wire on the sender, goes from the body to the frame work of the sender. this is all on the inside side of the sending unit. these break, but a small piece of 22ga wire and some solder fixed mine right up. also check the float, make sure its empty. you may have developed some pin holes that a dab of solder could fix up as well.

[Jeffc]

Agree with Trey,
Have you grounded the wire at the
tank and did your gauge rise?
If not the problem is with the gauge, or
wire to it,
or its power supply.
Also,
once the sender is out you can
check it to see if it is working
by using you volt/oms meter, ground
the neg side to the base and the
pos to the wire post,on the oms setting
meter needle
should swing with movement of arm.

Grounding of the sender is most often by
a strap between the sender tube and the
fuel line, stock would be a clip
that spans one to the other.

[rock]

Thank you Trey and Jeff,

Man what a nice thing to see such helpful answers so fast and on a holiday too! Lemme clarify your suggestion about "Have you grounded the wire at the tank and did your gauge rise?"

Is the suggestion here to pull the wire that runs from the threaded stud on the sending unit to the gage,(on the sending unit mine is kinda pushed on with a right angle rubber or plastic guard) and put maybe a short piece of wire inside the guard to allow me touch the wire inside the guard to a known good ground?

Reason I ask is if I do this while leaving the sending unit wire attached to the gage, and also leave the 12 volt hot line on the gage, and also leave the ground for the gage on its ground, I will have 2 grounds..one from the tank and one from the gage to the a good ground I wired in behind the panel. Thinking electrically I don't see what this would be doing that would be useful diagnostically...but it must be related to the little ground inside the tank that you are talking about.

Oh, if I pull the unit, can I make a new gasket out of gasket paper?

Thanks!
rock
'64d100

[wideblock]

rock, the gauge works by reading the amount of ground put up by the sending unit. if you pull the wire off the tank, and touch it to ground, your gauge should read full. ungrounded it will go to empty. yes, you have a positive and a ground at the gauge, this is to make the gauge work. the third wire that goes to the sending unit runs thru the resistor on the sending unit and is exposed to a variable ground as the arm rises and falls to give you the gauge reading. so if you slide a small piece of wire into that 90 degree boot at the sender, and touch it to good ground with the ignition on, your gauge will swing to full if its wired and working right. and yes, gasket paper works fine for a replacement. thats whats on mine

[Roger]

A general rule of thumb is the more gas in the tank, the lower the ohms resistance, the less gas in the tank the higher the ohms of resistance, if the gauge is functioning correctly.

[Russ]

"Reason I ask is if I do this while leaving the sending unit wire attached to the gage, and also leave the 12 volt hot line on the gage"

Rock, guages don't usually have the full battery voltage directly to them. Do your aftermarket guages say to hook them up that way? Be careful or you might damage your fuel sending unit.

You can't get a new sending unit for a Sweptline but there are places that rebuild them.

[wideblock]

russ, the gauge for my aux tank had both a positive and negative wire besides the sending unit wire. some of the newer gauges require thier own power to work. it also has a hot wire for the light.

[Jeffc]

Are we talking about a stock gauge set or aftermarket?

The stock set will have a 12volt supply reduced
by a voltage limiter (regualtor) built into the
gauge. The 3 posts on the stock gauge are as
follows:
>>marked 'a' top post supplies reduced voltage to
temp gauge.
>>marked 's' side post runs to tank.
>>post to alt gauge side is 12 volts in.
>>ground is though the gauge set mounting pod.

Aftermarket sets will very on setup.
some may or may not work right with
a 60s mopar tank sender.

As stated above, sending unit must be grounded
to work and unless the tank is well grounded
will not get enough of a ground to be reliable
just using the ring that holds to the tank.

If stock set, grounding the sending unit
wire will not damage anything since voltage
has all ready been reduced by the limiter
built into the gauge.
Testing a stock gauge
......
http://imageevent.com/jeffc/techstuff2e ... =4&s=0&z=2

[rock]

OK guys,

Here is a success story. Wouldn't have happened without the advice in the thread so THANK YOU THANK YOU. I realize I coulda just kept doing what I have done for 25 years...write down odometer at fillup and go what I know is limit (or less) before fillup. But with the new stainless dash insert and new AutoMeter gages, I just decided to be stubborn and get the gage to work.

First the measuring totally proved the sender was at fault. So, last week as a 70 degree week here in NC, truck got moved to clear yard, fire extinguisher at hand, and even scored a used unit. I thought I was gonna do a direct swap of old for newly scored sender til I pulled the old sender. ( A Ford sending unit wrench fits perfect BTW) Naturally the two are slightly different. Old has a right angle dog leg in pickup to shelter the float, newly scored not only was straight tube but angled to wrong side of tank. Not to worry. Tubing cutter took care of the too long problem, but I managed to separate the tube from the flat top. I considered swapping the rheostats, then checked resistance in both after opening them up. It seemed the old one could be carefully cleaned of oxidation, so I did clean it. Bingo, not exactly 73 -12 ohms, but not far. Certainly better than steady 43. Except float had a hole in it. Looking over the "new" float showed a hole in it too. Since it was solder at least one float, I decided to solder both and the loose top too. I considered silver solder and oxy acetlylene, but was afraid to melt the float, so out with the propane. Using non acid flux both floats and the top were soon soldered, then tested over night under water for good luck. No leaks in floats! SO, into tank, gage reads perfect from old unit, and even have a spare on shelf. Couldn't have happened with out you all, and of course, now it is 38 degrees with the winter winds from the west coming in. Time to read the forum posts!
rock
'64d100