fuel guage problems... about ready to give up.

[67chevy1series]

well heres the story. when i finally started to drive my truck i realized the fuel guage wasnt reading properly. so i took the original sending unit to the tank out and put a new one in. this one was a reproduction made for a 72 (has vent tube) so i put that one in and it didnt read right either. so i replaced the fuel guage. still didnt read right. so i bought another new sending unit that is a reproduction for a 67 (has no vent tube) this one worked for 3 days maybe 2 after i put it in. one morning driving to school i stopped to get some gas. i put 20 bucks of gas in and then turned the truck on and realized that my gauge started to read empty... so i was thinking how i could fix it, and thought maybe its the little resistor that goes from one of the metal studs to the other, on the back of the guages. so i replaced that with one that looked perfect, and still my guage read empty... so i kept driving and i noticed when i made turns it starts to read but once the gas in the tank levels it reads empty again. so i figured out that the little brass float in there was full of gas and just sinks. so i got another one and i submerged it in water to see if it would fill up with water or if it would float. it floated every single time i submerged it. so i figured, ok this ones good and i took the sending unit out of my truck and put the new brass float in..... STILL DOES NOT READ!!!! it still says empty!! and my wire is fine i checked the wire and it has no bare spots or anything im getting really tired of this and i am out of ideas and im just about ready to let the truck win the battle. PLEASE HELP ME.

[71 super]

Float. The repop floats are all trash. I have several that show good in water and end up sinking when in a tank. Take yours out and drill a small hole with a pin vise in it. Bet it has gas in it.
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[BADPURPLE70CHEVY]

Originally Posted by 71 super

Float. The repop floats are all trash. I have several that show good in water and end up sinking when in a tank. Take yours out and drill a small hole with a pin vise in it. Bet it has gas in it.
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71 super is correct. The repop ones tend to be terrible. Been down this road.

[mking]

Have you tried Taking the Sending unit out of the tank, Hooking it up and grounding it really good, then moving the float to see if it works then?
You have to move it pretty slow. If the gauge reading doesn't change, it's not the sending unit.
You said you changed the Fuel gauge in the dash. Is the replacement new or used?
If your sure the gauge is good, Check the ontinuity of the wire from the dash to the tank.

[davepl]

Just a "safety shout-out" here. Remember that the gauge uses a pretty serious resistor to limit current flow through the sender. You don't want to be "testing" anything here with a full unrestricted 12V, I don't think (not implying anyone suggested doing so, just in case there's a misunderstanding).

Electric Arcs + fuel vapor == Fastest path to an RIP thread.

I imagine you're fine if you're just testing with a multimeter or the original gauge output.

[Davemotohead]

Take the wire off the sending unit and ground it and watch the gauge,,I believe it should read full when grounded and empty when not grounded,,if the gauge works,,then its the float or sending unit,,are you sure you have the Unit grounded?

[VetteVet]

Originally Posted by Davemotohead

Take the wire off the sending unit and ground it and watch the gauge,,I believe it should read full when grounded and empty when not grounded,,if the gauge works,,then its the float or sending unit,,are you sure you have the Unit grounded?

You've got the right idea Dave but you have it backwards. The gauge should read past full when not grounded and empty when the sending wire is grounded.
The best thing to do is to pull the sending unit wire off at the fuse panel and turn the key on. The gauge should go past full. Then run a temporary wire from the fuse panel to a good ground and the gauge should go to empty. This isolates the gauge from the sending unit.

If this checks out then re-connect the sending wire to the fuse panel and disconnect it from the sending unit. If it reads past full then the sender is the problem and if it still shows empty then the sending unit wire is shorted to ground before it gets to the sender. A common problem in these old trucks and the wire runs under the left sill plate and is commonly shorted under there.

[67chevy1series]

well when i take the wire off (brown) the gauge reads full put as soon as i put the wire back on it starts to read empty evem though i am most certainly not empty.
so if the repop ones are all junk then what do i do? find a good original?

[diabloceto]

I had a problem like this with my sending unit and just about beat my brains out. What I finally figured out was that the metal strap that goes from the resistor to the lug at the top was touching one of the metal tubes cause it to not read empty. It is very easy while putting it in to bend that over and touch one of the metal tubes.

Diabloceto

[pritch]

Just throwing this out. On mine, it was driving me crazy for some time until I discovered this:



This is my printed circut board, and the line to the gauge is burned through. I put in a different one and now my gauge works perfect. I kinda found it by accedent-I was trying to figure out why the dash lights didn't all work.

[67chevy1series]

Well I'm pretty sure my metal line isn't touching. My circuit board is brand new as well lol
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[67chevy1series]

Ttt
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[luvbowties]

Originally Posted by 67chevy1series

well when i take the wire off (brown) the gauge reads full put as soon as i put the wire back on it starts to read empty evem though i am most certainly not empty.
so if the repop ones are all junk then what do i do? find a good original?

TESTS:
Disconnect brown wire at tank. With ignition turned ON, on these tests, ground it & gauge should read E. Loose & it should read FULL. If not, run new wire from tank to gauge, AFTER disconnecting original wire from gauge to tank at BOTH ends.

Disconnect brown wire at tank AND at gauge(cut it?) at a point close to gauge, but where you can be assured it is NOT grounded up to that point. Run a temporary wire from tank-side-of-gauge to tank "area". First, ground this wire, & ga. should read Empty. Loose, & it should read Full. If gauge reads as above, sender or wire along floor is grounded and GAUGE IS GOOD.

Now: If gauge reads correctly with temporary wire checks above, replace brown wire along floor to tank; or else, remove ALL that original wire(which is likely at least partly grounded somewhere along the floor) & bury this temporary wire carefully under carpet/mat.

If gauge does NOT read correctly when temp. wire is connected to tank, then SENDER IS BAD OR INCORRECTLY INSTALLED.

Next, after gauge is determined good and sender is determined bad or installed incorrectly: With sender removed AND hooked to gauge, float swung to lowest point should show Empty on gauge. Float swung to highest point should show Full on gauge. If this check works right, you are picking up an improper ground on the sender as you install it in tank; if it fails, your sender is bad.
HTH,
sam

[67chevy1series]

thank you for the write up!! ill try that

[67chevy1series]

well turns out that the new little brass canister i put on fills up with fuel to i dont knwo where to get a good one aty ive used all the "good" ones i had

[luvbowties]

Originally Posted by 67chevy1series

well turns out that the new little brass canister i put on fills up with fuel to i dont knwo where to get a good one aty ive used all the "good" ones i had

Find leaking hole, shake out gasoline, dry in sunshine, clean, and use proper flux-and-solder to solder hole. Should be good as new.
Else, if brass is too rotten, try local suppliers--be sure to check with NAPA first--and then order new from like LMC.
HTH,
sam

[67chevy1series]

Ok so I fixed the brass float... It's still doesn't work..
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[Fitz]

Originally Posted by davepl

Just a "safety shout-out" here. Remember that the gauge uses a pretty serious resistor to limit current flow through the sender. You don't want to be "testing" anything here with a full unrestricted 12V, I don't think (not implying anyone suggested doing so, just in case there's a misunderstanding).

Electric Arcs + fuel vapor == Fastest path to an RIP thread.

I imagine you're fine if you're just testing with a multimeter or the original gauge output.

Let's put it this way....if you perform that test near the tank with the sender out you will only do it one time......

[cdowns]

try running a ground wire from the sending unit to the the cab body

[68gmsee]

Just to throw out another possibility if all of the above suggestions don't resolve your problem. About 7-8 years ago, I bought a new sending unit and it didn't work. The resistor wire that the sending unit contacts ride on were crap and weren't any good.

I decided to get another one from a different vendor and this time it looked pretty decent. I metered it out with my ohms meter before I installed it. After I had it in I noticed it didn't work right either. showed almost empty on an almost full tank. I took it off again and found that the way the unit was manufactured, the arm was binding on the tank itself preventing float from moving. Had to reform the unit so it wouldn't hit the tank.

And one more thing... I took the sock off and installed an inline filter instead. Easier to change than the sock.
And one last thing... Make sure you have a good ground strap from engine to cab and the one from gauge panel to cab is installed.

[67chevy1series]

Ok tommorrow when I have some light out I will put a grounding wire from engine to cab and from gauges to dash
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[magwakeenercew2jh]

I've just been through this...And when I say THROUGH it, I mean it. The frustration is the worst part.

Here are a few ways to help get past the fits:

Remember that there are only three elements at work, here:

The sending unit;
The gage;
The wiring in between.

I'm not going to waste your or anyone else's time here on how to check out all the parts. Many good tips already. And good threads on the Forum to fill in the gaps.
But if you compartmentalize into these three elements, you'll fix the problem........*Before* you get blown up.

Sounds simple. And, yeah, this IS an over-simplification. But I'll tell you this:

With an inexpensive fuel gage from any of the Name Auto Zone Whatevers (that is, is you don't want to pull your out of the dash) matched to your new sending unit (90 ohm), a multi-meter with
an ohm read-out, and 12v (your battery) on your work bench, you'll figure out which of the three elements is the culprit.

My story ended up with my finding out that I had too much resistance in my fuse block caused by weather and grime, a bad sending unit, AND a screwed up gage. I kept plugging away, steam coming
from my ears...pissed at the supplier of the sending unit, etc. So, I was able to tell from the bench-testing that the semi-new gage I had from my stash of extra dashes, and the new sending unit were
operational. I almost gave up....after checking pins in the dash connectors, the printed circuit on the dash, the wiring from the fuse box to the sending unit, etc., etc., etc.

Then, I installed the M and H under-dash harness that included the fuse box. I was going to do that anyway, and I already had the harness. So, before I started direct wiring to the gage,
installation of the harness "magically" created the fix.

That's MY story and I'm sticking to it....Except the part about running out of gas...not *knowing* I was out of gas when I thought I had plenty... and coming home on the back of
a flat......er, never mind.