fuel gauge concern

[Eds56]

Hello everyone,

I just replaced the fuel tank, sending unit, fuel pump & in-line filter on my 56. How sensitive are the tri-five gauges? The reason I ask, is I have added about 8+ gallons of gas (aka liquid gold) and the gauge needle is just barely in front of the 1st dot (E). Prior to installing the sending unit, I ran a jumper wire to it and moved the float up and down by hand, while watching the gauge to make sure it works.(it did).

some things I have tried--
1.) un-hook the wire @ sending unit, the gauges needles goes past full.
2.) re-attach wire to ground and needle goes back to E.
3.) Added additional ground wire to one of the sending unit screws, but it didn't help.
4.) Slapped bottom of tank with rubber hammer, while helper was in the car watching the gauge and it didn't budge.
5.) tested sending unit before install, to verify gauge / unit works and they did.

Any suggestions??


Thanks in advance,
Ed

[567chevys]

Here are some pointers :

Gas Guage & Tank Sender Problems
Many Gas Gauge problems relate to the Gas tank Ground. Before you check anything else make sure the tank itself or at least the sender itself has a ground to the frame. It may be necessary in some cases to add a wire from one of the sender mounting screws to the frame. 55-57's use a 0 to 30 ohm setup that is not the most accurate arrangement and has not been used since the 50's. If you are having problems with accuracy you can correct this to some degree by adjusting the sender arm. This is a trial and error process that you can do after you are sure that both the gauge and the sender are basically functional. For example if the gauge is reading lower than the amount of gas that you know is in the tank, you would raise the gauge reading by bending the float arm down.
	To Check Gas Gauge: Take wire off of tank sender, leave it in the air not touching anything. Turn key on, gauge should go to past full. Touch sender wire to frame {full ground}, turn key on, gauge should read empty. If wiring and tank ground is good then sender is not working. If you suspect the wiring this check should repeated by removing wires at gauge.
Trouble Shooting Gas Gauge: FUEL GAUGE Checklist with Ignition 'ON'. Gauge pegs itself to the right, above full, some possibilities are: Brown wire is off back of gauge. Poor connection at underdash to tail lamp harness plug. Brown wire is broken between gauge and sending unit. Brown wire is off of the sending unit. Bad tank to body ground. Sending unit is bad. Gauge pegs itself below empty, some possibilities are: Brown and pink wires are swapped on back of gauge ('55 & '56) Brown and tan wires are swapped on back of gauge ('57) Gauge reads 'E' all the time, some possibilities are: Brown sender wire is shorted to ground. Sending unit is 'stuck' or defective. Gauge won't budge when the ignition is turned on, some possibilities are: Pink wire is off of gauge or switch is defective ('55-'56). Tan wire is off of gauge or switch is defective ('57). Gauge is bad. Gauge 'bumps' but will not read at 'E' or above, it may be: Gauge is bad ​Hope this help's ! Sid

[chevynut]

As I understand it the sender is supposed to have a resistance of 0-30 ohms. Since you put in 8 gallons, it should be half full or about 15 ohms. You might check the sender wire to ground and see what the resistance is. If it's ok, your gauge may be bad.

[Eds56]

Thank you Sid & CN,

I'll take a stab at some of these trouble shooting items and report back later in the week.

Ed

[Eds56]

Hey everyone,

My troubleshooting has been delayed due to my employer actually expecting me to work this week....the nerve of some people.

Anyways, I added a ground wire from the frame to one of the sending unit screws just to make sure I do have a good ground. I also unhooked the sending unit wire a time or 2 and got conflicting results. The first time the gauge pegged past full (as it should)....then the next few times it didn't budge off E at all. SO my next step is tracing the sending unit wire back & see if I can find a short. I will also be removing the gauge cluster to check the gauge itself later in the week.

Thanks again for the tips.

Ed

[Rick_L]

The other half of this discussion is the adjustment of the float arm.

The float needs to be at the bottom of the tank when the gauge reads empty.

If the float runs out of travel (arm incorrectly bent upward), the gauge will read too low through the whole travel. (it may still read full when full, but the needle will drop fast as you drive.) The float arm needs to be bent down to correct that.

If the float has too much travel (arm incorrectly bent downward), the gauge will read too high through the whole travel. The gauge will still show quarter or half tank when you are really empty. The float arm needs to be bent upward to correct that.

You may have the first problem.

This assumes the float arm length is correct, and it is on the stock sender.

[Eds56]

Thanks Rick,

That's on my list to check this weekend.

[Eds56]

Update for any that are interested--

I found the root cause, it turned out to be a short on the sender unit wire inside the tank. Apparently it had a nic on it and was shorting against the tube/bracket area. I bent it away and recoated that area of strap...put it back in and it works just fine now. Shows me to have 1/2 tank, which is correct by ChevyNuts earlier post.

Thanks again to ALL of you who took time to offer suggestions.

Ed