2005 freightliner columbia with low voltage reading

I have a 2005 Freightliner Columbia, with a 14l Detroit 60 Series. Recently, it started reading a low voltage on the cluster. While accelerating (empty or loaded) voltage would drop to 11 point something. Then when throttle reduced, it would climb back up to 13.8-14 volts. After while even at idle it would just sit at 12.5 volts and, of course drop to low 11s while accelerating. Now, after you start the truck (at 12.4 volts) just sitting there, and within a few minutes it drops to below 9 volts and dies. It's got a new alternator and batteries ( all withing a 4 or 5 weeks. Cleaned battery cables and frame ground from battery. It reads 14+ volts at the alternator, starter and #1 battery. I'm gonna change the starter when I get back to west Texas Wednesday as my driver said the solenoid was much hotter than the rest of the starter. The reason I changed the alternator, is because when I first started troubleshooting, I could disconnect the batteries and It would continue running. The other day, I disconnected the battery and it died. If anyone has any other ideas as to what may be the cause, your experience and knowledge would be greatly appreciated.

 

How tight is the belt that turns the ALT. If you can get someone that has the tool that hooks behind the belt and reads how much the spring in belt tensioner has in it, if you haven't replaced it and the belt now would be the time to catch up on repairs

 

It's pretty tight. Tensioner is new. Thought about changing the belt out just in case it's glazed. But, figured it wouldn't volt out at 14 volts if that was the case. I had volted it out at idle and high idle. It remained reading 14.1 at 700 and 1500 rpms.

 

Changed starter. Voltage still low. Disconnected battery ground to frame, Voltage goes up. Disconnected main battery wire... no change. Disconnect main ground and main power... truck dies. Get 14+ volts at alternator, starter, secondary mag switch, battery and fuse box. Can the low voltage disconnect cause a low voltage situation?

 

Really bad disconnecting batteries with the engine running. Good way to spike the alternator or ECM and fry them.

 

Yessir, but was at wits end...

 

After changing starter. Volts went to 11.8 volts at highest but didn't have major volt drop anymore that would kill the truck. Found a bad battery, changed it.... 12.5 volts at highest, dropping to 11.7 lowest while driving. Changed battery interconnect cables, and now we sit at 13.5 and 13.3 lowest while high RPM. Gonna clean the egr and blow put egr cooler then drive it and find out. The egr is not related my issue... just some PM..

 

So you founded new battery that was bad?

 

I’m keeping my eyes on this bc I have the same issue with my 2006. What’s a secondary mag?

 

Wound up being just the battery interconnect cable. Once it ran a while. Went up to 13.7-14 volts idle or pull.