Gas gague troubles.
 

This week my trucks gas gague has been kind of acting up. It pegs way past full. Then when I turn it off the gague will some times go back to where the needle should be pointing. Could this be a ground issue? It was working this morning on the way to school.

Re: Gas gague troubles.
 

A bad ground will cause them to read below empty all the time is what I've typically seen. Check the connector on top of the sending unit to see if it's loose/corroded.

Re: Gas gague troubles.
 

Also make sure that this thing is plugged into the firewall. After a recent carb swap on my 77, I had the same problem with the gas gauge showing WAY above full. After I plugged this in, all was well.

Re: Gas gague troubles.
 

short the sending unit to ground = empty,
unhook it it will go over full


but what does that wire hook to?

Re: Gas gague troubles.
 

On my '85, there is a single-wire connector, orange wire just barely accessible between the cab and bed. When that comes disconnected from it's post on top of the tank, the gauge will do what you described, read way over past full. I'm betting your problem lies there as well.

creativity will be required to get it reconnected if it came off, or needs to come off.

Re: Gas gague troubles.
 

Get a 6 or 7 year old kid to reach in there and plug it back in. :lol: Otherwise you may need to loosen the bed bolts and raise it a few inches.

Re: Gas gague troubles.
 

thanks everyone for your input, im trying all your ideas so keep em coming!!!

Re: Gas gague troubles.
 

If that don't fix could have a faulty sending unit. That is a bit more to check but not that bad yet.

Re: Gas gague troubles.
 

Its normal if at full its past F for a good while. i have to use 5 gallons before my truck hits Full when its off it goes down slightly

Re: Gas gague troubles.
 

I heard an interview with a Ford engineer on NPR a couple months ago who said that drivers have an expectation of "fullness" on the gauge when the tank is filled up, and an inclination to run the vehicle to the limit on empty. This is apparently a kind of "getting your money's worth" from a tank of gas mentality.
So Ford, and all other vehicle manufacturers, purposely design the fuel gauges/sending units to overestimate the fuel level when the tank is filled up ("I got my money's worth") and underestimate the fuel level when the tank is near empty ("I better get some gas soon before I run out"). Human psychology in automotive design.

Re: Gas gague troubles.
 

that seems logical i've panicked thinking i was out of gas but i got another 110 miles on the tank after it had read empty.

Re: Gas gague troubles.
 

I read the same thing in one of my mid 70s Chevrolet Service News publications. GM re-calibrated the CK truck fuel gauge and sender system around somwhere between 74 & 78 so that F-1/2 was more like F-5/8 or F-11/16. That makes 1/2-E actually 3/8-E or 5/16-E in the tank. That's why the bottom half of the gauge drops so fast.
A direct result of the artificial OPEC oil shortages in 1974.

Back on topic.

A loose or pinched sender wire and a loose or missing ground will cause the gauge to peg intermittently. The tank can still ground poorly through contact on the straps and frame. I had this happen with my 1985 C10 after i replaced the tank. The ground was completely missing from the old tank. After I installed a ground strap from the frame to the sender my problem went away.

Re: Gas gague troubles.
 

Yea the ground wire could be bad. Multimeter could be your best friend.

Re: Gas gague troubles.
 

Yea it doesn't sound like a ground it sounds like the power wire coming out of your tank hopefully. Cause if it's sending unit have to pull the bed or drop the tank!
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