Calibrate fuel sending unit?

[Spartan]

Well, this has been the latest I have had my 69 on the road in the 24 years I have owned it.  I had it out for a spin Christmas eve (not a typical Michigan winter).  I had my gauges done a year ago and hooked them up but the gas gauge always registered empty, even before I had them done so I figured the wiring was jacked.  I was going to go through everything next spring when I put in my rear defrost and took out the heater box. 

I was tooling around a bit and since I did not put allot of miles on I figured I had gas left.....well, I ran out about a block from the house.  After I put 5 gallons in, I took it to the gas station and filled it up for the the rest of the winter but when it is full, it registers now but at a 1/2 tank.  I knew the gauge tested ok when it was bench tested before and after the refirb was done (hence the wiring) but now, since it is regestering, I am wondering if the new sending unit that was put in two years ago needs to be calibrated.  All the other gauges (except the tic-toc, I need to add the wiring to the engine) work.

Does the sender need adjusting or is it still a wiring issue?

[resq302]

Could be a couple of things.  The ground clip was known to never make a good connection.  That is the thin metal wire that goes from the sending unit tube to the metal fuel line tube and acts as a jumper wire where the rubber fuel line is between the steel line and sending unit.  It could also be that the float on the sending unit is leaking which is not allowing the sending unit to register correctly.

[Just 6T9 CHGR]

Sometimes ( in my case as well) the float arm needs some minor tweeking to register the correct reading

[TylerCharger69]

resq302.....I always thought that was a clip to hold the lines together.....I never knew it was an actual ground!!!    We learn something new everyday I s'pose!!!

[Plumcrazy]

resq302.....I always thought that was a clip to hold the lines together.....I never knew it was an actual ground!!!    We learn something new everyday I s'pose!!!

Correct.   But that also means the fuel line must be grounded too.

I would try taking a 10 ohm resistor and connecting it between the wire that attaches to the sending unit and a good ground.  That should put the fuel gauge at it's full reading.

[SFbullitt]

I went through the same exact issue with my 68.  New guages, new sending unit, tank lines etc....  It was doing the same thing yours is.  I bought the ground strap, nothing.  Even grounded the wire from the batt. directyly to the float to test is....still no go.

Here is what is most likely the issue.  The float in your sender could have developed pinholes and the floater is weighed down by fuel.  It's acting as a sponge and not letting it rise above the fuel when you have a full tank.  Next time you have an empty tank, drop it down, remove the sending unit and raise it by hand with the ignition on.  It will most likey return to the F position.  If this is the case, replace the float.  If it lingers around 1/4 tank then drops to E quickly this is most likely the issue.

[Spartan]

Thanks for the info guys.  I should have tried all that when I ran out of gas, hehehe.   I will play around with this during the next warm spell and see if I can get it to work correctly.

[TylerCharger69]

resq302.....I always thought that was a clip to hold the lines together.....I never knew it was an actual ground!!!    We learn something new everyday I s'pose!!!

Correct.   But that also means the fuel line must be grounded too.

I would try taking a 10 ohm resistor and connecting it between the wire that attaches to the sending unit and a good ground.  That should put the fuel gauge at it's full reading.

Let me hijack for a second....I need to tell you that about 3/8 of my fuel line coming to the pump is rubber fuel line,  and is also rubber coming out of the pump,  then filter, then carb.   So basically  most of the entire line is rubber.   Can this have negative effects?...Because if so...I'll put steel lines back on from the tank up.   Everything runs fine,  but...could it possibly run better?  FYI   both rubber and steel lines are the same diameter.

[Plumcrazy]

resq302.....I always thought that was a clip to hold the lines together.....I never knew it was an actual ground!!!    We learn something new everyday I s'pose!!!

Correct.   But that also means the fuel line must be grounded too.

I would try taking a 10 ohm resistor and connecting it between the wire that attaches to the sending unit and a good ground.  That should put the fuel gauge at it's full reading.

Let me hijack for a second....I need to tell you that about 3/8 of my fuel line coming to the pump is rubber fuel line,  and is also rubber coming out of the pump,  then filter, then carb.   So basically  most of the entire line is rubber.   Can this have negative effects?...Because if so...I'll put steel lines back on from the tank up.   Everything runs fine,  but...could it possibly run better?  FYI   both rubber and steel lines are the same diameter.

You could just attach a wire between the sending unit and body and supply the ground that way.

[resq302]

resq302.....I always thought that was a clip to hold the lines together.....I never knew it was an actual ground!!!    We learn something new everyday I s'pose!!!

Correct.   But that also means the fuel line must be grounded too.

I would try taking a 10 ohm resistor and connecting it between the wire that attaches to the sending unit and a good ground.  That should put the fuel gauge at it's full reading.

Let me hijack for a second....I need to tell you that about 3/8 of my fuel line coming to the pump is rubber fuel line,  and is also rubber coming out of the pump,  then filter, then carb.   So basically  most of the entire line is rubber.   Can this have negative effects?...Because if so...I'll put steel lines back on from the tank up.   Everything runs fine,  but...could it possibly run better?  FYI   both rubber and steel lines are the same diameter.

You could just attach a wire between the sending unit and body and supply the ground that way.

I actually tried that.  Seemed to get a better reading but still not 100% accurate.  Mine just might need to be tweaked a bit though at the sending unit to adjust it to the propper reading.