74 Lesabre Fuel Gauge acting up

[JoelsBuicks]

About a month ago my fuel gauge on my 74 Lesabre went haywire. Upon filling my tank, the gauge reads way above full and stays that way for well over a half tank's worth of driving (see pic).

 

Then at some point, it quickly comes down to a full reading and usually doesn't get below about 5/8 reading even when the car is near empty.  

 

Any experience with this kind of behavior?  Maybe a bad float or something that ethanol could have created?  I got the car two years ago and have only put about 3500 miles on it.  Before that, it was driven about 300 miles since 1980 and none after 1994. 

 

Thanks,

Joel

[Beemon]

Check the ground to the sending unit. You may have to drop the tank and hope it's the sending unit.

[EmTee]

I agree with Ben -- reading too 'full' is usually indicative of a poor ground to the tank sender.  Try adding a jumper wire between the metal fuel line and the body near the tank and see if that helps.

[avgwarhawk]

Ground wire. 

[NTX5467]

I'm wondering if the rheostat on the sender itself (inside the tank) might not have some corrosion on it, which is "short circuiting" the resistance to read "Full"?

 

When you get the sender out, you might be surprised how dainty those contacts are! 

 

IF you do pull the (near empty!) tank, also replace the fuel line from the tank unit to the metal chassis fuel line!  It needs the upgraded ethanol-resistant rubber line as the old line is not ethanol resistant and will start to seep after exposure to the modern gasolines . . . which happened on my '77 Camaro about 10 years ago.  When I'd go home for lunch, I'd come back out and smell gas, but nothing on the ground (as it had evaporated) but I also noticed a drop in fuel economy.

 

Ethanol "cleans and dries" the rubber hose from the inside out on rubber items.  What might look good at first glance might be ready to flake off the outer layer of rubber on the hose.

 

NTX5467

[JohnD1956]

I thought I documented changing the sending unit on my 72 Electra, but I cannot find the posts and pictures from the past.  so here they are again.

 

Likely, you have the same problem I had when I got the Electra.  While my sender got stuck in different orientations than yours it acted just as erratic.  When bringing the car home form Oregon sometimes the gauge would not move to full in the 200 miles before I refilled it.  So upon disassembly I found that the float is contained in a canister.  And the float would get stuck on the square shaft at the center.  I tried to whittle the inside edges of the float with some light grit sandpaper, but just could not get it to move smoothly, so I replaced it with what's currently available aftermarket.  

 

[JohnD1956]

Word of warning on the aftermarket senders.  The available senders are more conventional in design, and do not have this container.  I found that there were several available at different price levels.  I chose a middle priced unit since they all looked alike in the pictures.

 

Now my gauge fluctuates wildly during driving.  Obviously the container acted like a baffle system and moderated the gas level around the original float.  I do not know if the higher priced pickups have a tighter pivot point on the float to reduce some of this annoying gauge action.  I also do not know if anything can be done with the aftermarket pickups to mitigate this issue.  But for the most part I can read the gas level with some confidence.

[JoelsBuicks]

Thank you all very much.  I'll first try better grounding and if that's not it then down comes the tank.  I do need to change that fuel line.  My 60 Electra started panoramic seeping - hose would be all wet but never dripped. 

 

Joel