[grd777]

when the car is off (key out ) it reads 1/4 tank, which is correct .when i start the car it goes to full . i have replaced the tank and the sending unit ,it it also grounded .what should i check

[johnta1]

Does it go past full with key on?


If so probably disconnected wire at sender or broken wire.

[grd777]

Originally Posted by johnta1

Does it go past full with key on?


If so probably disconnected wire at sender or broken wire.

no stays at full

[johnta1]

Is the tank full?



I'd check that there is 12 volts at the dark brown wire at the gauge. The tan wire goes to the sender at the tank. The dash gauge needs to be grounded to dash and dash should have a ground also.

The sender on gas tank should be grounded also. The ground point may be corroded?

If the tan wire is grounded it should show empty I believe. (zero resistance)

At 'Full' it shows 90 ohms to the gauge.

[johnta1]

If it is at Full, the sender may be stuck up which would show full I guess?
(if the others stuff checks out OK)

[grd777]

Originally Posted by johnta1

If it is at Full, the sender may be stuck up which would show full I guess?
(if the others stuff checks out OK)

i will add more gas and see if it goes up

[Transamric]

Originally Posted by grd777

when the car is off (key out ) it reads 1/4 tank, which is correct .when i start the car it goes to full . i have replaced the tank and the sending unit ,it it also grounded .what should i check

Is the new sender an aftermarket replacement or a NOS GM?

[grd777]

Originally Posted by Transamric

Is the new sender an aftermarket replacement or a NOS GM?

aftermarket

[Transamric]

That may be the problem. It took me 3 senders to get one to read accurately on my '70.

[grd777]

Originally Posted by Transamric

That may be the problem. It took me 3 senders to get one to read accurately on my '70.

ok that will be a pain if i have to replace it . is anything i can try before i do

[Trevor78]

A faulty ground, or disconnected ground wire at the sender would cause the needle to max out, off the face of the gauge, and not change if keys removed. The fact it drops again to what is assumed the correct level, shows that something is being introduced to the feed that shouldn't be there with ignition, a crossed-wired somewhere perhaps, but where, no idea. I guess that could also be at the sender itself. Was you harness to it still intact, has the rubber boot?

[grd777]

Originally Posted by Trevor78

A faulty ground, or disconnected ground wire at the sender would cause the needle to max out, off the face of the gauge, and not change if keys removed. The fact it drops again to what is assumed the correct level, shows that something is being introduced to the feed that shouldn't be there with ignition, a crossed-wired somewhere perhaps, but where, no idea. I guess that could also be at the sender itself. Was you harness to it still intact, has the rubber boot?

yes i am thinking something like that. now i need to find out step by step

[Trevor78]

Some simple tests, that don't tell much, is to disconnect the sender wire at the trunk harness. With ignition, the gauge will max out, and without power, should stay there. Plugged back in, when working normally, it would pull back down to correct level. Normally.

[grd777]

Originally Posted by Trevor78

Some simple tests, that don't tell much, is to disconnect the sender wire at the trunk harness. With ignition, the gauge will max out, and without power, should stay there. Plugged back in, when working normally, it would pull back down to correct level. Normally.

k thanks will give it a shoot

[tdavidl]

i hope you can get it to work...if not, its not the end of the world...mine works, however, i don't know if mine is original or an aftermarket...same with gas tank & i don't have 100% confidence in how it reads so i just make sure i fill the tank every times to odometer turns over another 100 miles...never have to worry if the gas gauge us accurate then :-)

[grd777]

Originally Posted by tdavidl

i hope you can get it to work...if not, its not the end of the world...mine works, however, i don't know if mine is original or an aftermarket...same with gas tank & i don't have 100% confidence in how it reads so i just make sure i fill the tank every times to odometer turns over another 100 miles...never have to worry if the gas gauge us accurate then :-)

yes one of my cars in the past had this issue and i seemed to mange ,thanks for reminding me

[Formulabruce]

Sender GROUND is at Back of unibody near the tail panel on a unibody extension, not far from filler neck.

[grd777]

Originally Posted by Formulabruce

Sender GROUND is at Back of unibody near the tail panel on a unibody extension, not far from filler neck.

yes i see it will try to clean it up