wandering fuel guage

[window5]

When i fill the tank the guage reads full but it either will stay full or only go down to half way mark it . but if i turn off the ingnition it goes straight to empty. any ideas. Thanks Paul 2000 gmc safari 4.3 2wd.

[Matrixx]

Hi window5

It sounds very much like a faulty sending unit, but you need to make certain first.

You can check the harness plug-in underneath the vehicle just before the tank and make sure it has a good connection. Also check and make sure the ground wire that leads from the harness that bolts to the body isn't corroded in anyway, this can cause problems as well.

I'm sure others will chime in if they can.

Please keep us updated, thanks.

[window5]

Thanks will check the plug today and the ground wire. if it is the sending uni how big of a pain in the butt is it to replace?
Thanks Paul

[astro355]

I like the fuel tanks on these vans. They are a lot easier to work on there a lot of other vehicles on the road.

Two straps hold it on. It's best to soak the nuts/bolts with PB Blaster (or other penetrating oil) a week before you intend to work on it.

Once you are ready to remove, put a floor jack with some blocks under it to secure it. Obviously, if there's fuel in it, that will just add weight which is why I use the jack. Undo the two straps and the filler tube. Drop it down a couple inches so you can remove the rubber hoses without stretching anything and unplug the harness. Let the tank down slowly so your sure nothing is hanging you up and then the tanks out.

Before you remove the sending unit from the tank, clean, clean, clean the top of the tank. You don't want any crud falling into the tank. Using a screwdriver (punch) and hammer, knock the retaining ring around until the releases the sending unit and carefully pull it out. Congratulations, its a sending unit!

While you are under there, you might as well inspect the rear brake line that is above the fuel tank. They like to rust thru there.

[Big_kid]

Like Astro355 said. I've done at least half a dozen different tanks, and the Astro is BY FAR the easiest one. I'm also not in the rust belt, so the PB blaster wasn't an absolute necessity for me, but it did help.

[window5]

thanks to all that have responded. i did go under and check all connections and all is well. i guess i will go and get a sending unit and a case of beer>
Thanks Paul

[jcivince]

I had the same issue with my gas gauge. It didn't really bother me so I didn't mess with it. When replacing the brake lines to the rear I did replace the sending unit and it started working just fine.

[toddb]

Mines fine, only thing though, is when I first start it on empty it says I have a 1/4 tank - it does slowly read right. Almost run out of gas because of this. Even though I know this it has nearly gotten me more then a couple of times.

[ghostrider1061]

sounds like a loose ground wire to me. next time your tank is about empty, drop it and trace down the ground wire. it should be the one welded to your tank. it should be connected firmly and tightly to yoour frame. remove it and check the connection for rust or any other crud that can prevent a good metal to metal ground.

[RichinMD]

Using a screwdriver (punch) and hammer, knock the retaining ring around until the releases the sending unit and carefully pull it out.

I prefer a brass rod personally to avoid sparks. Vapors and sparks = bad news. I found a threaded brass rod about 1/4' diameter and 12" long at my local hardware store for about 2 bucks.

As for dropping the tank, I have a small floor jack and had to use a piece of plywood cut into the distance between straps to help spread the weight to initially lower it, then used some 2x4's to drop it all the way to the ground. After that I was able to access all my lines somewhat conveniently.

While you have the tank open, you may as well inspect for any debris in the bottom and try to get it out. Also, when was the last time you changed the fuel pump? Again, as long as you have the tank down, that may be something to think about since you are looking at a sending unit anyway. Regardless of what you do, I would recommend changing the fuel filter after the first run through of the tank to ensure any debris that did get sucked through doesn't cause you grief in the future.

One last trick that I do to avoid running out of gas, I religiously refill my tank at 400 miles or 1/4 tank whichever comes first, so at least if my gauge goes out, I know I have xxx amount of miles to go before I have to fill up(I love trip odometers!).

my

[Stuart]

I'm having trouble with mine as well. It bounces back and forth, between reading correctly, and being maxed out at the full mark. When reading correctly, I've noticed the needle wandering by 1/8 tank, and also moving in time to the turn signal. I'm thinking (and hoping) that it is ground related... any thoughts?

[sieng]

My fuel gauge reads correct but the needle vibrates back and forth in a high frequency. Also, when this problem started, the needle would max out way beyond the full mark when I engage the starter. Once running, it would read the correct amount but have this vibration. Anyone have any ideas.