Fuel gauge

[givengold]

My fuel gauge just stopped working. I did a visual check of the fuses, everything looks OK. Where do I look next?
'77 stepside, big block, dual tanks.
Thank you,
Dan

[old Rusty C10]

is there any change with switching the tanks?

[BGRAFX]

I'm looking for a similar answer, mine is readiing a 1/4tank low. so is it the guage or the fuse or the sending unit?

[givengold]

No, the gauge does not move for either tank. It is pinned all the way to the right (past full).

[Zman86]

having a similar problem with mine. Replaced the gauge with another I had, same thing. I've not gotten any further into the problem.

[asphaltburner]

Yo! Wow! Just posted this info in pokethesmot's post. Pegged beyond full is an indication of an open circuit, and is usually attributed to a bad ground on the inner frame. Could be a bad sender if you've not replaced it already, or could be a damaged pink (or light brown) sender wire between the gauge and sender.
Todd.

[givengold]

Todd,
Thank you for the info. I will check those issues ASAP.
Dan

[68 TT]

Originally Posted by BGRAFX

I'm looking for a similar answer, mine is readiing a 1/4tank low. so is it the guage or the fuse or the sending unit?

I had one that only moved a 1/4 tank for its entire range. Within that range it was accurate on how much was in that tank.

Turned out the float had a leak in it and was partially submerged in fuel. Check the float in the tank.

[joe231]

a leaky float will give you low readings.....as Todd stated, pegged to full is an open circuit, and since both tanks show the same look at what is in common for both tanks...which is also what Todd had said

[asphaltburner]

Yo! Dudes!
The new senders that I bought have solid floats so they'll never leak, so replacing old senders (if inaccurate or malfunctioning) would sure be a plus. LMC and Classic Industries have them. They ARE, however, $70 each.
Todd.

[joe231]

Soild?
what is it made of?

[asphaltburner]

Yo! Some kinda very dense material, shaped like a roll. Doesn't seem porous,...cool, huh?
Todd.

[joe231]

yeah, that is wild

[asphaltburner]

Yo! joe231!
I just LOVE applying new technology to my 30+ year old vehicles!!
Todd.

[joe231]

Heck yeah!!

[givengold]

I found it. A spliced section of wire was missing running along the frame between the passenger side tank and the firewall.

[68 TT]

Glad to hear it was something easy.

Dropping the tank sucks especially if it has much fuel in it.

I just helped a friend change the in tank pump on his late 90's Chevy van. It has a 100 gallon tank and we could only get 50 gallons out of it with all the gas cans in the neighborhood so we still had probably 35 gallons to deal with. Good thing I had a tranny jack.

[asphaltburner]

Yo! Far out!
Todd.

[bigred1957]

Originally Posted by 68 TT

I had one that only moved a 1/4 tank for its entire range. Within that range it was accurate on how much was in that tank.

Turned out the float had a leak in it and was partially submerged in fuel. Check the float in the tank.

Mine did the same exact thing, read a bit over a 1/4 a tank to empty through the full range sweep. I tried a new sender it did the same so I know it's not the float. The wiring checked out but have'nt checked the gauge. Anyone know how to test the gauge? In or out of the truck?

[oldwagon]

Hey guys, along the same lines, when I start out with a full tank, the gauge works fine; however, when the gauge drops to about 3/8 of a tank full, it will start fluttering real bad. Any possibilities?

[68 TT]

Originally Posted by oldwagon

Hey guys, along the same lines, when I start out with a full tank, the gauge works fine; however, when the gauge drops to about 3/8 of a tank full, it will start fluttering real bad. Any possibilities?

Sounds like a bad spot in the float level rheostat.

[motornut]

an open/cut sending wire will max out over full
a grounded wire will go empty
a flutter might need a ground in the cluster
may want to try adding a ground behind it..... there they all go to one

[jesse977]

I just went through this...my fuel gauge was stuck at 1/4 and didnt move at all. The culprit was the wire that goes from sending unit to dash.

[wilkin250r]

Originally Posted by bigred1957

Mine did the same exact thing, read a bit over a 1/4 a tank to empty through the full range sweep. I tried a new sender it did the same so I know it's not the float. The wiring checked out but have'nt checked the gauge. Anyone know how to test the gauge? In or out of the truck?

The gauge is fairly simple. The sending unit is basically a variable resistor ranging from 0 ohms at full, 90 ohms at empty (with 45 ohms being half full, ect ect). So all the gauge does is read that resistance. To test the gauge, you just pull the sending unit out of the circuit and replace it with a known resistance.

You can accomplish this by pulling the actual wire off the sending unit and connect a resistance to ground, and this will not only test the gauge, but also all the wiring associated with all of it. Variable resistors (also called Rheostats or Potentiometers, or pots for short) are only a few bucks from Radio Shack, the hardest part is making sure you're showing the gauge a realistic resistance. Keeping within 0-90 ohms is going to be difficult with a potentiometer that ranges from 0-100,000 ohms. If that's your choice, you might actually be better off buying a selection of fixed resistors and using them.

Let me know if you want more help, not only am I an electrical engineer, I just recently fixed a similar issue on my 79 squarebody. I had to replace the sending unit, along with most of the wiring all the way to the dash (luckily, my gauge was still functional).

[bigred1957]

Resistance makes sense, both my new and old rheostats do the same thing. The full sweep ranges from empty to just above a quarter tank, but it still is a full sweep (i.e. the gauge isn't stuck at a quarter a tank until the tank reaches a quarter, it sweeps the entire capacity of the tank). Wouldn't that mean added resistance in the gauge or printed circuit?