2000 K3500 7.4l
Just noticed it.
Turn key on, gauge shows full.
Start engine, still full.
Run for around 5 minutes, or more, and it drops to empty.
A few seconds later it goes back to full.
It's a random thing.
The fuel pump was changed about a year ago.
I think it was an Airtex aftermarket pump.
Any ideas????

 

Airtex does not have a good reputation for their fuel pumps. It could be the sending unit on the fuel pump or possibly the stepper motor for the gauge. Another possibility is in the wiring.

 

I tried it this morning, and now the needle didn't even move.
I missed the days when vehicles were more reliable.

 

If you moved the wires around and it quit working completely, this is where you should keep looking.

 

Didn't move any wires.
Truck doesn't move much.
Probably hasn't moved in over a month.