Voltmeter drops to 9 volts on Chev 454 P30 motorhome

14 is good, (10 is bad). Any other issues with the electrical system?
The gauge may just be off a little. If you put a voltmeter on the battery with engine running, it should show anywhere from about 13.5-14.5 volts. That's the alternator output to charge the battery and run the car's electrical systems.
If voltage truly dropped to 10 volts when car was running, I think your check engine light would come on, and there would be serious issues with lights flickering and dimming. Check the alternator output. Good luck.

The diagnostic procedure for EI (electronic ignition) systems varies depending on the vehicle make and model year. Always follow the procedure recommended in the vehicle manufacturer's service manual.
The following procedure is based on Chrysler EI systems. The crankshaft timing sensor and camshaft reference sensor in these systems are modified Hall-effect switches.
If a crank or cam sensor fails, the engine will not start. both of these sensor circuits can be checked with a voltmeter or lab scope.
If the sensors are receiving the correct amount of voltage and have good low-resistance ground circuits, their output should be a pulsing digital signal or voltmeter reading while the engine is cranking.
If any of these conditions do not exist, the circuit needs to be repaired or the sensor needs to be replaced. When the engine fails to start, follow these steps:

1. Check for fault codes 11 and 43.
   • Code 11, "Ignition Reference Signal," could be caused by a defective camshaft reference signal or crankshaft timing sensor signal.
   • Code 43 is caused by low primary current in coil number 1, 2 or 3.
2. With the engine cranking, check the voltage from the orange wire to ground on the crankshaft timing sensor and the camshaft reference sensor. Crankshaft timing and camshaft reference sensor terminals.
   • Over 7V is satisfactory.
   • If the voltage is less than specified, repeat the test with the voltmeter connected from PCM (powertrain control module) terminal 7 to ground.
   • If the voltage is satisfactory at terminal 7 but low at the sensor orange wire, repair the open circuit or high resistance in the orange wire.
   • If the voltage is low at terminal 7, the PCM may need replacement.
     • Be sure 12V are supplied to the PCM terminal 3 with the ignition switch off or on, and 12 V must be supplied to PCM terminal 9 with the ignition switch on.
     • Check PCM ground connections on terminals 11 and 12 before PCM replacement.
3. With the ignition switch on, check the voltage drop across the ground circuit (black/light blue wire) on the crankshaft timing sensor and the camshaft reference sensor.
   • A reading below 0.2V is satisfactory.

NOTE When using a digital voltmeter to check a crankshaft or camshaft sensor signal, crank the engine a very small amount at a time and observe the voltmeter. The voltmeter reading should cycle from almost 0 volts to a highter voltage of about 5 volts. Since digital voltmeters do not react instantly, it is difficult to see the change in voltmeter reading if the engine is cranked continually.

1. If the readings in the previous two steps are satisfactory, connect a lab scope or digital voltmeter from the gray/black wire on the crankshaft timing sensor and the tan/yellow wire on the camshaft reference sensor to ground. Lab scope patterns from the camshaft and crankshaft position sensors.
   • When the engine is cranking, a digital pattern should be displayed or the voltmeter should cycle between 0 and 5 volts.
   • If the voltage does not cycle, sensor replacement is required.
   • Each sensor voltage signal should cycle from low voltage to high voltage as the engine is cranked.

A no-start condition can occur if the PCM "locks up."

• In step 2 above, if 0 volts is indicated the PCM may be faulty or it may be locked up.
• If the PCM is locked up it will not store a fault code for the reason.
• Basically, the PCM will lock up when it goes into a safeguard routine if the 9-volt or 5-volt reference voltage shorts to ground. This shuts down the PCM to protect it. Since it shuts down, no DTCs (Diagnostic trouble code) are stored.
• The engine will not start as long as the ground is present. An intermittent ground will cause the engine to stop running.
• Attempting to restart the engine without cycling the ignition switch to the full LOCK position will not start the engine, even if the ground is lifted.
  • Cycle the ignition switch to the LOCK position and wait about 5 to 10 seconds.
  • If the ground is lifted, the PCM will reset and the engine will start and run until the ground occurs again.
• On 1996 and new SBEC III and JTEC engine controllers, there are two 5-volt reference signals. The sensors that require 5 volts are separated, thus If this signal shorts to ground the engine will still stop running, but for the first time a DTC can be set.
• Also note, if the 9-volt reference voltage is opened, there will be no DTC stored for the crankshaft or camshaft positions sensors. With an open circuit the PCM cannot tell if the engine is cranking or not. The diagnostic routing does not begin until the PCM senses engine cranking.

For a car to start you need compression spark and fuel. If you put a rag over the schrader valve (looks like a bike tire air valve) on the metal fuel rail and push the center down with a screw driver gas should shoot out if it doesn't you have a fuel problem.They make a spark tester that goes in line between the plug and wire see if you have spark when it cranks. Look up on line for a picture of the crank sensor at auto parts web site and look for sensor front of engine just above oil pan

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check with voltmeter to see if you have 12 volts at battery with engine off.

check for 14 1/2 volts with engine running at1500 rpms.

Report results

When your engine is running, you should have around 14.2-14.5 volts using a voltmeter across the + and - terminals on the battery. If it is around 12, you have a bad alternator, blown alternator fuse, or alternator wiring fault.

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

Battery light indicates alternator failure. If you have a voltmeter, check voltage at battery with engine running. Should be at least 14 volts. If no voltmeter, remove alternator and take it to parts store for testing.
If the alternator is bad and that is your only problem, the truck should jump start, but it will not go far unless the battery is charged. OK?

It sounds like your alternator is not kicking in when the truck first starts. There is a wire that "tickles" the alternator to get it charging when you first start the truck, however it will start charging without that once you rev the engine up. A couple of good shots with the fuel pedal should snap the guage up to 14. If it climbs up slowly to 14 then the alternator is starting to wear out or you have poor contact.Get the alternator tested for output. If it's okay take the wires off the alternator and battery and clean up the ends so you have bare shiny metal and clamp them back down tight. Make sure you have radio codes and procedures before you unhook the battery. Hope this helps.

No-Start Diagnosis
The diagnostic procedure for EI (electronic ignition) systems varies depending on the vehicle make and model year. Always follow the procedure recommended in the vehicle manufacturer's service manual.
The following procedure is based on Chrysler EI systems. The crankshaft timing sensor and camshaft reference sensor in these systems are modified Hall-effect switches.
If a crank or cam sensor fails, the engine will not start. both of these sensor circuits can be checked with a voltmeter or lab scope.
If the sensors are receiving the correct amount of voltage and have good low-resistance ground circuits, their output should be a pulsing digital signal or voltmeter reading while the engine is cranking.
If any of these conditions do not exist, the circuit needs to be repaired or the sensor needs to be replaced. When the engine fails to start, follow these steps:

1. Check for fault codes 11 and 43.
   • Code 11, "Ignition Reference Signal," could be caused by a defective camshaft reference signal or crankshaft timing sensor signal.
   • Code 43 is caused by low primary current in coil number 1, 2 or 3.
2. With the engine cranking, check the voltage from the orange wire to ground on the crankshaft timing sensor and the camshaft reference sensor. Crankshaft timing and camshaft reference sensor terminals.
   • Over 7V is satisfactory.
   • If the voltage is less than specified, repeat the test with the voltmeter connected from PCM (powertrain control module) terminal 7 to ground.
   • If the voltage is satisfactory at terminal 7 but low at the sensor orange wire, repair the open circuit or high resistance in the orange wire.
   • If the voltage is low at terminal 7, the PCM may need replacement.
     • Be sure 12V are supplied to the PCM terminal 3 with the ignition switch off or on, and 12 V must be supplied to PCM terminal 9 with the ignition switch on.
     • Check PCM ground connections on terminals 11 and 12 before PCM replacement.
3. With the ignition switch on, check the voltage drop across the ground circuit (black/light blue wire) on the crankshaft timing sensor and the camshaft reference sensor.
   • A reading below 0.2V is satisfactory.

NOTE When using a digital voltmeter to check a crankshaft or camshaft sensor signal, crank the engine a very small amount at a time and observe the voltmeter. The voltmeter reading should cycle from almost 0 volts to a highter voltage of about 5 volts. Since digital voltmeters do not react instantly, it is difficult to see the change in voltmeter reading if the engine is cranked continually.

1. If the readings in the previous two steps are satisfactory, connect a lab scope or digital voltmeter from the gray/black wire on the crankshaft timing sensor and the tan/yellow wire on the camshaft reference sensor to ground. Lab scope patterns from the camshaft and crankshaft position sensors.
   • When the engine is cranking, a digital pattern should be displayed or the voltmeter should cycle between 0 and 5 volts.
   • If the voltage does not cycle, sensor replacement is required.
   • Each sensor voltage signal should cycle from low voltage to high voltage as the engine is cranked.

A no-start condition can occur if the PCM "locks up."

• In step 2 above, if 0 volts is indicated the PCM may be faulty or it may be locked up.
• If the PCM is locked up it will not store a fault code for the reason.
• Basically, the PCM will lock up when it goes into a safeguard routine if the 9-volt or 5-volt reference voltage shorts to ground. This shuts down the PCM to protect it. Since it shuts down, no DTCs (Diagnostic trouble code) are stored.
• The engine will not start as long as the ground is present. An intermittent ground will cause the engine to stop running.
• Attempting to restart the engine without cycling the ignition switch to the full LOCK position will not start the engine, even if the ground is lifted.
  • Cycle the ignition switch to the LOCK position and wait about 5 to 10 seconds.
  • If the ground is lifted, the PCM will reset and the engine will start and run until the ground occurs again.
• On 1996 and new SBEC III and JTEC engine controllers, there are two 5-volt reference signals. The sensors that require 5 volts are separated, thus If this signal shorts to ground the engine will still stop running, but for the first time a DTC can be set.
• Also note, if the 9-volt reference voltage is opened, there will be no DTC stored for the crankshaft or camshaft positions sensors. With an open circuit the PCM cannot tell if the engine is cranking or not. The diagnostic routing does not begin until the PCM senses engine cranking.

Check fuel pressure. Sounds like a bad pump or plugged fuel filter.

Hello, 9-10 volts is not enough to keep a modern vehicle running. Taking in consideration the age and model of this truck, it could easily be an alternator failure.
I hope this helps.
CYA Gator241