Question about 1994 Chevrolet C/K 3500

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Voltmeter drops to 9 volts on Chev 454 P30 motorhome

The voltmeter starts off at about 14 volts. After the engine is running for about 10 minutes the voltmeter will drop to about 9 volts. Maybe 20 minutes later it will jump back up to 14 volts for two or three minutes. Any ideas what could be causing this?

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  • geomail65 Apr 27, 2009

    Thanks for the help

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This is eithere a loose positive cable from the altenator to the battery or the regulator in the altenator is about to fail. if you have not had any problems starting the vehicle then most likely its a loose connection between the gauge and the charginging circuit or the gauge is faulty. take a multimeter and test the charging votage at the altenator while the vehicle is running it should measure 13.5 volts and should not change more than .5 volts. if the voltage drops more than 1 volt the regulater is bad and the altenator needs to be replaced. if it is working fine then looke for a bad connection make sure all positive and ground cables are tight. if they are replace amp gauge

Posted on Apr 19, 2009

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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.
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I have a 2006 chrysler 300 2.7 engine it did not start up change spark plugs


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. fr_24.13.gif 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. fr_24.14.gif 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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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. fr_24.13.gif 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.
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  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.
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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. fr_24.14.gif 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.
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    • 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.

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