Fuel gauge stuck in a full position, did I just get lucky?

[cubandeathgrip]

Now I never have to worry about an empty tank again!



Tho..Seriously my gas gauge is stuck full it may move an eighth or a 10th of a position but it never goes past that point, just happen a few days ago thinking it may go away, just wondering what I should check for.. bad gauge or a bad sending unit?

thanks

 

[Schurkey]

Gauge past "Full" is typically a broken wire between gauge and sending unit, or a broken ground wire.

When that was my '88, the wire was broken along the frame rail, just below the driver's feet. But the break can be anywhere.

 

[xXxPARAGONxXx]

Now I never have to worry about an empty tank again!



Tho..Seriously my gas gauge is stuck full it may move an eighth or a 10th of a position but it never goes past that point, just happen a few days ago thinking it may go away, just wondering what I should check for.. bad gauge or a bad sending unit?

thanks

Mine's the same way since I bought it used.

Subscribed.

 

[1500z71]

If it’s stuck full that would indicate it’s receiving constant voltage wouldn’t it? Does it drop when the key is off or stay up?

 

[Schurkey]

The older fuel gauges are magnetically-driven. Constant power is given to one side of the gauge, which is counterbalanced by variable power to the other side.

The fuel tank sending unit works on a "0-to-90 ohm" resistor, that resistor controls the variable power to the gauge. "0" ohms produces maximum current, and therefore maximum electromagnetic power. The needle goes to "E". "90" ohms produces minimum current, minimum electromagnetic power, the needle goes to "F".

When the wire (including the sending unit ground wire) or the connections along it become corroded, resistance increases, current decreases, and the gauge reads more "Full" than is accurate. If the wire breaks completely, current flow goes to zero, and the gauge goes past Full and stays there.

 

[454cid]

The older fuel gauges are magnetically-driven. Constant power is given to one side of the gauge, which is counterbalanced by variable power to the other side.

The fuel tank sending unit works on a "0-to-90 ohm" resistor, that resistor controls the variable power to the gauge. "0" ohms produces maximum current, and therefore maximum electromagnetic power. The needle goes to "E". "90" ohms produces minimum current, minimum electromagnetic power, the needle goes to "F".

When the wire (including the sending unit ground wire) or the connections along it become corroded, resistance increases, current decreases, and the gauge reads more "Full" than is accurate. If the wire breaks completely, current flow goes to zero, and the gauge goes past Full and stays there.

OP has a 98.... I think that's the later style, like mine. It's something like 40-to-200 ohms (I checked it when I replaced my tank). I believe it feeds the PCM. Mine is working a little wonky lately, and I think it's the air core motor. It's vibrated for years, but now it shows way past full, works it way to empty, yet somehow I can't get any where near the tank capacity in it.

 

[smdk2500]

but now it shows way past full, works it way to empty, yet somehow I can't get any where near the tank capacity in it.

Both my 95's doe this. I've just accepted when it shows a 1/4 tank I need to go to a station and fill up. I wish that they would read at the full mark when full not past it. I don't trust that if they go that far past full that when it shows 1/4 tank that it actually is a quarter. I feel that it is amost empty since I put 28-30 gallons in. With diesel prices right now my 6.5 hardly ever sees a full tank anymore.

 

[Frank Enstein]

I have modified all my sending units to read more accurately and in every case the arm for the sending unit is too long.
That makes the one in the Astro a real M#&%@^*#@*er to install. I nearly doubled the length of the arm using my antique coat hanger collection to make a new arm on all of them.

When functioning as Generous Motors intended they stay full far longer than is real and drop like a stone under 1/2 tank.
Three Quarters on the gauge is more like a half tank.

Supposedly this is to make you think that your brand new GM vehicle is getting better mileage than it really does.
I don't recall the source of the info but it seems to make sense to me.
My 77 Catalina ex-cop car was the exception. When the gauge read E you were walking!

 

[454cid]

Both my 95's doe this. I've just accepted when it shows a 1/4 tank I need to go to a station and fill up. I wish that they would read at the full mark when full not past it. I don't trust that if they go that far past full that when it shows 1/4 tank that it actually is a quarter. I feel that it is amost empty since I put 28-30 gallons in. With diesel prices right now my 6.5 hardly ever sees a full tank anymore.

Thats actually the opposite of what mine does. Mine is reading about empty, but then I "fill" my 32gallon tank with only about 20 gallons.

 

[HotWheelsBurban]

I have modified all my sending units to read more accurately and in every case the arm for the sending unit is too long.
That makes the one in the Astro a real M#&%@^*#@*er to install. I nearly doubled the length of the arm using my antique coat hanger collection to make a new arm on all of them.

When functioning as Generous Motors intended they stay full far longer than is real and drop like a stone under 1/2 tank.
Three Quarters on the gauge is more like a half tank.

Supposedly this is to make you think that your brand new GM vehicle is getting better mileage than it really does.
I don't recall the source of the info but it seems to make sense to me.
My 77 Catalina ex-cop car was the exception. When the gauge read E you were walking!

Yes we noticed this on many of our GM vehicles. The gauge on this Burb is pretty accurate though; if it's reading half down, I can put in 20 gallons and it's real close to full.