2004 9200i international

Something is wrong with your ECM power feed. Check your battery connections, and check the ECM power wires and fuses at the batteries too. The volt gauge is reading data from the ECM. The volt gauge shows exactly what the ECM is getting for power.

 

Check altenator output

 

Check your voltages. A bad alternator or a bad battery is possible. Corroded cables maybe. ECM is possible but I would look at the others first. They're way cheaper to fix if needed.

Was told your gauge will move more under throttle due to the injectors pulling more juice. I'm still learning the ins and outs of this thing called a truck. So, take that with a grain of salt.

As for the beeps, I've got an 05 9200. I get three beeps like I'm low on fuel pretty much within the first 5 minutes of starting the truck. EVERY time. Just ignore it, it won't go away.