Fuel gauge

[motornut]

In high school i put a switch in, that grounded the sending unit
leaving school tank would read empty,
buddies cough up a few bucks for a drive home ,stop for gas"click"
u got gas,read as normal lol

When i change /remove a gas tank/sending unit
I will bend up the float rod an inch or more
this will leave you more gas below empty,rather then gas over the full
for 2 reasons
1.more gas in tank less chance of freeze up at -40
2.at almost a 1/4 tank ,to me it's like having the reserve on a motor bike lol

doing this the needle will go empty to full still ,
just now you might not have to walk @ E.
lol

you can use the (prob almost any simular gm type)float out of the tank as well for testing
and the wrong float, not long enough, won't drop enough, either
dirt,rust,other debris

[oldwagon]

Thanks guys. Looks like there is a number of things I can look at.

[wilkin250r]

Originally Posted by 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?

First of all, I'm pretty sure I had it backwards. 0 ohms is empty, 90 ohms is full (mods, can we edit my last post in this thread, then also get rid of this disclaimer for future people searching for answers?)

Additional resistance would just read higher. Instead of ranging from 0-90 ohms, you'd be ranging from 60-150 ohms, so your tank would always look more full than it is. You'd basically read from 3/4 to full.

Is it possible you have an old 30-ohm sending unit? They were used I believe before 1965.

You can do some really simple tests to check the gauge. Pulling the wire off the sending unit should peg the fuel gauge to full full full. The gauge is expecting to see 90 ohms at full, and you're showing it a million ohms (open circuit).

Likewise, taking the wire from the sending unit and shorting it to ground should peg the gauge at empty. The gauge is expecting zero ohms at empty, and that's exactly what you're doing. Sending it to zero ohms.

[bigred1957]

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?

Figured mine out finally, ended up being a tiny bit of resistance at the gauge connections. Pulled off the printed circuit and cleaned all the contacts. Works fine now. Wish I would have figured that out sooner.....