Gas guage with dual tanks

[mikedag]

Hello,
I recently acquired a 86 Chev with the dual tank system and I have a couple of questions/concerns.

The first being the fuel gauge. It seems to come and go. For example I'll start the truck and it will be on empty (tank is actually full), and if I start it again immediately after the gauge could read full and go to empty within minutes of driving. Switching tanks makes no difference. To my understanding this is a problem with the gauge because it is consistent with both tanks....am I correct? could it be a bad connection?

The second concern is when switching the solenoid over it sometimes makes no noise and other times makes a loud buzzing noise....Is this an indication that it is crapping out and I should be investing in a new one?

I don't know much about this system so I am looking to you gents for help,
Mike Dagenais

[motornut]

Hi welcome
I've heard of lots of issues coming down to ground problems
one is the gauge bouncing,when driving,i'd check your grounds...add one behind the cluster

[VetteVet]

It does sound like a grounding problem but too much ground rather than no ground.
Testing the fuel gauge is pretty simple. If you pull the fuel gauge wire off at the fuse panel fuel terminal then the gauge would go to way past full. This is the no ground symptom.

Yours is hanging on empty which is too much ground and the fuel sender wire is grounding on the truck somewhere instead of grounding through the sending unit resistor. I would trace the wire from the tank sending unit switch and see if it has worn of the insulation and is touching the truck frame or the cab. The wires run under the trim piece on the left door rocker and are notorious for shorting to the cab.

I've got a diagram of the dual tank valve on the tank, if I can find it I'll post it.