Vold meter drops for a few seconds

[MegaCummins]

When it's cold outside and I'm warming my truck up before driving I my volt meter drop down to like what looks like 8-10 volts then the guage goes back to 14 and over. If my lights are on it becomes real evident that there is a huge draw on the ele. sys. for a few seconds the goes back to normal. It cycles like this for a while then goes away. Is this something that was designed in the truck or do I need to start being concerned? This is my first winter with this truck?

 

[Al Dahl]

grid heater

That is your gridheater its normal till it warms up

 

[SWithrow]

If you have a multi-meter and you test from the batteries you will see that the truck is charging despite what the dash gauge indicates while warming up.

 

[LRutigliano]

If you have a multi-meter and you test from the batteries you will see that the truck is charging despite what the dash gauge indicates while warming up.

X2 !!



Gauge shows way less than 14V, but voltmeter on battery terminals shows 14. 95 volts...

 

[jelag]

This is how I understand it.....

At cold engine start, Cummins wishes to keep some of the load off the engine for the first 2-3 minutes of operation and the ecm limits the alternator output until the engine is stable and can handle the load... . thus you have low voltage as the engine and all accessories for those 2 or 3 minutes are running off the batteries... the heater grid is a high current device and the voltage will drop when the grid cycles...

After the 2 or 3 minute time out, the engine has stabilized and smoothed out... the grid heater turns off and the ecm allows full alternator output and the voltage rises to 14+ volts. .

I own several of these truck and they all do this... but each varies in the exact time and sequence as they are all different years...

Hope this helps. .

 

[CBowden]

Trust me I live in Montana and unless I plug my truck in when I go and start it my voltage meter will go down several times before it warms up then back to normal. Only happens in the winter. If you leave your truck outside at home and have a block heater I suggest plugging it in at night.



Like Jim and others have said this is normal



Brian

 

[rbattelle]

At cold engine start, Cummins wishes to keep some of the load off the engine for the first 2-3 minutes of operation and the ecm limits the alternator output until the engine is stable and can handle the load... . thus you have low voltage as the engine and all accessories for those 2 or 3 minutes are running off the batteries... the heater grid is a high current device and the voltage will drop when the grid cycles...

Are we sure that's how it's programmed? I can't find this description anywhere in the factory manuals.



I've always been under the impression that the voltmeter is deliberately suppressed during the post heat cycle so people don't see the needle bouncing around while the grids cycle. Here's what the factory manual says:

On vehicles equipped with the optional diesel engine, the ECM is programmed to restrict the voltage gauge needle to a position above the graduation on the far left end of the gauge scale and suppress the check engine indicator operation until after the engine intake manifold air heater has completed a pre-heat or post-heat cycle.

I can't find anything that talks about what the alternator behavior is during these cycles, but I've always assumed that its output current is a function of the battery temperature sensors. In fact, the charging voltage varies inversely with the battery temperature.



Ryan

 

[SWithrow]

Put your multi meter on your battery terminals then start your truck, you will see that it is charging from the very beginning.