Fuel sending unit woes

[gcsupraman]

I just installed a new sending unit for the 1972 K20. Old unit would often get stuck and wasn't very accurate. The new unit came with a return that I didn't have, but a trip to the auto parts store solved that issue.

After installing the new unit I filled the truck up with fuel and the gauge reads about 3/4 full.

Where should I start? Should I try to test the sending unit? The thought of removing the sending unit isn't very appealing right now

Thanks

-Greg

[68gmsee]

When I installed mine, it read off like that and found out the float was hitting the side of the tank when it went upwards. I had to remove it and reform the float mounting wire/rod.

From http://www.chevytrucks.org/tech/gasgauge.htm

When the gauge reads lower than it should, check at the gauge by disconnecting the wiring from the tank unit. Turn the ignition on and if the needle reads full or above, the gauge unit is probably good and the tank unit or the wiring leading to it are probably the problem. Reconnect the tank unit wire to the gauge before proceeding.

Another good site for info. http://www.6066gmcguy.org/Electrical-02.htm

[gcsupraman]

Originally Posted by 68gmsee

When I installed mine, it read off like that and found out the float was hitting the side of the tank when it went upwards. I had to remove it and reform the float mounting wire/rod.

From http://www.chevytrucks.org/tech/gasgauge.htm

When the gauge reads lower than it should, check at the gauge by disconnecting the wiring from the tank unit. Turn the ignition on and if the needle reads full or above, the gauge unit is probably good and the tank unit or the wiring leading to it are probably the problem. Reconnect the tank unit wire to the gauge before proceeding.

Another good site for info. http://www.6066gmcguy.org/Electrical-02.htm

How were you able to determine it was hitting?

I had to slightly bend the hard fuel line so I could get the unit to seat in the tank - they must use super metal because that damn line was tough to bend!!! I never thought about the float being stuck.

The unit is reading 28 ohms in it's current position when running a meter between the sending unit wire and the unit flange. With the wire disconnected the gauge goes past full - with the wire grounded it goes to empty so that should be normal according to what i have been reading.

I guess I will need to remove the unit again once I drive some more and the gas level goes down to see if it's rubbing.

Thanks for your help - I am very frustrated!

-Greg

[68gmsee]

If the gauge goes past full when disconnected the problem is in the sending unilt. I forgot to mention that this was the second unit I had ordered. The first one was crap. Didn't register correctly.

It's been many years but I believe I compared the old one to the new one to determine that it was rubbing the tank.

[gcsupraman]

Originally Posted by 68gmsee

If the gauge goes past full when disconnected the problem is in the sending unilt. I forgot to mention that this was the second unit I had ordered. The first one was crap. Didn't register correctly.

It's been many years but I believe I compared the old one to the new one to determine that it was rubbing the tank.

I drained some gas and removed the sending unit. I grounded it outside the tank while hooked up. when I move the float down, gauge reads empty. When its all the way up, gauge reads 3/4. I ohmd it...when the float is down it reads close to zero. When raised it reads around 30.

Looks like it's a bad unit?

-Greg