Gas Gauge Stuck On Full

[808humbo1]

I'm pretty sure this has already been asked many, many times but i cant seem to find the threads.....

my gas gauge is stuck on full.......

any suggestions/answers to why this is or where i should start? should i just order a fuel sending unit? thanks!

[dmack91]

Is it on Full, or beyond (at 3 o'clock)?

3 o'clock probably means the sender is open (no resistance) or beyond spec.

Put an ohm meter on the sending unit stud to ground. It should be 0-90 ohms.

If stuck at full, it could also be a sending unit float that is hung up.

[bosco200]

A gas gauge that always says full.....what are you complaining about

[LockDoc]

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LockDoc

[808humbo1]

Originally Posted by bosco200

A gas gauge that always says full.....what are you complaining about

hahhaha...i had to think about this for a couple seconds....but then i got it.....

[808humbo1]

Originally Posted by dmack91

Is it on Full, or beyond (at 3 o'clock)?

3 o'clock probably means the sender is open (no resistance) or beyond spec.

Put an ohm meter on the sending unit stud to ground. It should be 0-90 ohms.

If stuck at full, it could also be a sending unit float that is hung up.

its at 3 oclock......so does that mean i need a new sending unit?

[808humbo1]

Originally Posted by LockDoc

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Could be a wire problem, some people have had the wire short out under the sill plate at the drivers door. This causes the wire to ground out and the gauge read full. This usually makes the needle go past the full mark as dmack91 mentioned.

LockDoc

so how would i fix this?

[ol'blu72]

If i remember right full means an open circuit and empty means it is grounded out. Check your connection to the sender it may have come off and check for breaks in the wire or other connections coming off. You should be able to touch the wire to the sending unit to a ground and the gauge will go to empty.

[ol'blu72]

I did more looking. Pull the wire off the sending unit and touch it to ground it should go to empty, if it does more than likely the sending unit isnt grounded well to the tank (you can use a jumper to give it a good ground). If it doesn't go to empty look for a break in the wire tracing it all the way to the gauge cluster. hope this helps! My gauge is stuck on empty so I have been looking for a grounded out wire for a while.

[dmack91]

Originally Posted by ol'blu72

I did more looking. Pull the wire off the sending unit and touch it to ground it should go to empty, if it does more than likely the sending unit isnt grounded well to the tank (you can use a jumper to give it a good ground). If it doesn't go to empty look for a break in the wire tracing it all the way to the gauge cluster. hope this helps! My gauge is stuck on empty so I have been looking for a grounded out wire for a while.

Also, check the sending unit by pulling the wire, then run an ohm meter from the post to ground. If it doesn't read between 0-90 ohms, the sender is shot.

[Legolas894]

Fuel senders aren't all that expensive. I had one that had a rough spot on the resistor so it would seem to work fine until that magic amount of gas was in the tank and then it would go to full for a bit until you hit a bump.

All the advice on this post is good. Touch the sending wire to ground, it should read empty. Put an ohmeter on the sender and see what it reads. You can take it out of the tank and manually move it up and down to see what it's reading.

I had a sender rebuilt, changed the resistor on the back of the fuel gauge etc. The new sender worked the best.

Also, make sure you have gas in it!!

[altownsend]

I have read the posts because I have a similar problem. My problem is as follows: (there is about 3/4 tank of fuel)
With key off, the fuel gauge needle is past the full position.
With key on, the fuel gauge needle is still past the full position.

Troubleshooting:
I took the Sender Lead wire off, Ground wire still connected. With key in the On position, I grounded the Lead wire to the Sender's housing and watched the fuel gauge needle swing to the Empty position. When I removed the Sender Lead from Ground, the Needle quickly went back to the past full position.

When I reconnect the Sender Lead wire, turn key to the On position, the fuel gauge needle stays in the past full position.

The Sender is about 1 year old. Everything was working fine a week ago. Anyone have an idea of what I need to do?

[68gmsee]

If you touched the wire at the sending unit to ground and needle went to empty and hooked it back up and it went past full, you have either a defective sending unit or stuck sending unit arm. If the variable resistive windings are broken it would be like a full tank but check the arm to make sure it's bent away from tank sides. You can also check it outside the tank to insure it's working properly with an ohm meter.

I bought a sending unit several years ago that was defective. I had to piece parts off my old one to make it work. On another truck I installed a new one and the arm was not bent right.

[Sammy]

Common place for a break in the wire is under the sill plate on the drivers side. Maybe WES or GMC Paul has a source for decent sending units but the few new ones I have received in the past, I have checked the ohms reading's are seldom correct. And the fuel bowls/ pods have had pin holes seems to be common place. Just a few pointers to let you be aware a replacement might not be up to working standards if you end up down that road. Good Luck.

[WIDESIDE72]

Dead thread revival!!!

Im having trouble getting the gas gauge in my 72 working. It has a new blazer tank and sender in the rear, new sending wire, used gas gauge. I bought the truck INOP, so no way to compare before/ after. When I reinstalled everything, the gas gauge goes to three o'clock. When I tried two other used clusters, they did not move (stayed at 12 o'clock (?) (These clusters are of unknown condition as well.) Before I installed the bed wood, I made sure to scrape the paint off the frame and securely fasten the ground wire from the sender to the frame. When I unplug the wire that goes to the sender in the rear and ground the terminal on the fuse panel, nothing happens. I'm wondering if I have multiple problems (!)

[WIDESIDE72]

FYI I have a used OEM gauge cluster with a new repro printed circuit board.

[1972BlueC20]

I ran a wire from a bolt on the back of the fuel gauge housing to bare metal on the bottom of the dash by the parking brake release handle to make sure my gauge was properly grounded.

Just thought I'd throw that in, not sure if it's related to your issue

[LockDoc]

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Do you have a ground wire from the engine block to the frame? Engine block to cab? Two important ones....

Below is a picture of the ground wire for the instrument cluster to the dash.

LockDoc

[WIDESIDE72]

I did not have a ground from the cluster to the dash! I didn't see where there was a provision for one, but I added one to one of the mounting screws for one of the tins to the dash as mentioned above. The gauge now show 1/4 tank. We'll see what happens when I fill up! Thanks everyone for the help!

This weekend I plan to finish my side marker fuel filler mod. I already have the fuel door almost finished. I just need to work on the filler tube.

[LockDoc]

Originally Posted by WIDESIDE72

I did not have a ground from the cluster to the dash! I didn't see where there was a provision for one, but I added one to one of the mounting screws for one of the tins to the dash as mentioned above. The gauge now show 1/4 tank. We'll see what happens when I fill up! Thanks everyone for the help!

This weekend I plan to finish my side marker fuel filler mod. I already have the fuel door almost finished. I just need to work on the filler tube.

I hope you found the problem. Let us know.

LockDoc

[bigmac73]

Originally Posted by LockDoc

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Do you have a ground wire from the engine block to the frame? Engine block to cab? Two important ones....

Below is a picture of the ground wire for the instrument cluster to the dash.

LockDoc

where does that wire connect to in the instrument cluster?

[LockDoc]

Originally Posted by bigmac73

where does that wire connect to in the instrument cluster?

If you look close at the picture you can see it in the cluster plug. The black wire.

LockDoc

[bill3rail]

Originally Posted by LockDoc

If you look close at the picture you can see it in the cluster plug. The black wire.

LockDoc

To rehash an older topic,
My gas gauge was at 3:00 (Way past full).
I did some searching on 67-72 and found a few threads with information.
Ultimately I found it was the wire from the sending unit fell off the fuse box (Probably my ham-fisted working under the dash knocked it off).
See the attachment spade marked "Fuel Ga" on the left side of picture.
Thanks, Bill

[ballencd]

Can I bring this up again......
1991 Suburban, fuel gauge at about 3 o'clock position. When I turn the key on it moves a bit more clockwise. I assume that the sending unit is bad or the wire open between the gauge and tank but don't know where the plug is to test best. Not much room between the tank and body. There is a two (2) wire plug inside the frame on drivers side at front of the tank. One is for the fuel pump because when I disconnect it the vehicle will not start. Is other the gauge wire? I looks like its beige with white stripe?
Any Ideas??
ballencd

[ballencd]

Folks,

I pulled the cluster today and grounded the sending unit wire to chassis and the gauge went from 3'oclock to empty.
So
1) the wire from the rear is open or
2) the the sending unit has a bad ground or
3) the sending unit is bad.
Anyone know what wire I test at the tank? Looks like maybe a beige w/white stripe and a pink wire coming from the tank and headed forward past the drivers side rear spring shackle. I can see the ground screw and it looks to be good but I have not cleaned it yet.
ballencd