Alternator/charging question

hummin cummins

hummin cummins

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Dec 17, 2006
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01 with a new alt (that has been tested) 2 new batteries. It's charging at the batteries but on the gauge it shows only 10v at start up and gradually goes down to 8 and the check gauges light comes on. Any ideas? Thanks
 
I had the same issue with my 99. I swapped the batteries and installed a new high amp alternator which took care of the problem. I also had problems with TC lockup before the new alternator. Now it's great.

I had my old alt tested too, and it tested ok, but wouldn't charge in the truck. I was told that it was a problem with the diode.
 
Bad pcm or bad grounds. Check gauges. Hold down trip/odometer, turn key on and "check" will show. Release button and it will run through the gauge test. Probably pcm reporting voltage improperly.
 
Thanks, I will check these on monday. Will it give me a code so I might know whats wrong when I run the test on the gauges?
 
Mine threw 0622-Gen field circuit open and 1594- Charging system voltage high. But my gauges test gave no code. The gauges were fine, which led me to the PCM. There is a company in Alabama that has pcm and then Auto Mobile Source in Florida that has them also. I have used Auto Mobile Source for PCM and ECM and have had no problems at all.
Also check for ac feedback at batteries. That will show a field short in a diode or issue with the alternator that the "tested good alternator" didn't pick up. 12.5 volts on static batteries, 13.5-14.2 volts on charging batteries and less than .1 AC volts on batteries during charging state. Any more than .1 AC volts, you have an alternator issue. The voltage regulator is in the PCM for triggering charge and no charge from alternator. You can install an external regulator from a 80s model dodge/chrysler and bypass the PCM voltage regulator. Your lights will probably surge brighter and dimmer, but it will allow you to drive the truck and charge the batteries and everything else will work without causing more damage to anything.
 
jesnic said:
Mine threw 0622-Gen field circuit open and 1594- Charging system voltage high. But my gauges test gave no code. The gauges were fine, which led me to the PCM. There is a company in Alabama that has pcm and then Auto Mobile Source in Florida that has them also. I have used Auto Mobile Source for PCM and ECM and have had no problems at all.
Also check for ac feedback at batteries. That will show a field short in a diode or issue with the alternator that the "tested good alternator" didn't pick up. 12.5 volts on static batteries, 13.5-14.2 volts on charging batteries and less than .1 AC volts on batteries during charging state. Any more than .1 AC volts, you have an alternator issue. The voltage regulator is in the PCM for triggering charge and no charge from alternator. You can install an external regulator from a 80s model dodge/chrysler and bypass the PCM voltage regulator. Your lights will probably surge brighter and dimmer, but it will allow you to drive the truck and charge the batteries and everything else will work without causing more damage to anything.
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Thanks, I'll check this tomorrow. I think there is a place in Columbus In. where my brother gets his pcm's from if i need one. I've tried the external regulator before and the lights did surge, so I'll just get a pcm if I need one.
 
My truck charges the right battery at 15.02v and the left battery at 15v. This concerns me because I always believed 13.2-14.5 was good charging voltage for an alternator. My gauge has always seemed to read right about the 15v mark though. What's your voltage at the batteries? Static and running? You said it was charging at the batteries just not showing on the gauge in your first post.
 
If the temp outside is cold, the batteries have a harder time taking voltage. The pcm gets a signal from the battery temp sensor and tells the alternator to increase voltage, up to 15 volts, until the battery temp increases. When the battery temp sensor sees the increase in temp, the voltage supplied from the altenator should drop back to 13.5-14.7 volts. Moparman1973 has a full write up on it and tests to perform to validate altenator is charging properly.
 
skav said:
I also had problems with TC lockup before the new alternator.
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Not to de-rail but would you mind explaining the problems you had with tc lockup? Im having issues staying in lockup. Also having charging problems at idle.
 
Make sure the power lead to the underhood fuse box qnd the in cab fuse box is making a good conection. If not it.can throw the voltage gauge off.
 
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