LMM: Alternator???

[twest42271]

When I start my truck in the morning or after sittin all day the truck will not charge for about 5 minutes then go right up to 14. And when it's warm and I start it. It goes up in about 30 seconds. Had alternator checked but it checked good. But by the time I made it to napa it was already charging. Do I need a new alternator? Thanks and god bless

 

[hondarider552]

Well, if its charging, probably don't need a new alternator.

Are you sure its that? How old are the batteries? I would test those too... make sure to unhook them separately as well..

 

[LWATSON]

Is there some kind of regulator that can be causing problems?

 

[Darius6t9]

Probably just the intake heater and glow plugs still on till everything gets warmer in the combustion chamber. Or however all that works. Mine does the same thing. Has for as long as I have owned it. It is charging, just being pulled down by those things stated above.

 

[THEFERMANATOR]

If it's a stock truck, and cold out. There is a chance your intake heater is drawing it down for that period and preventing it from bringing the voltage up. It sounds liek your alternator is fine from your description, but the ECM may be keeping it offline until the intake heater is shut off(haven't logged an LMM in cold enough weather to know if the intake heater will do this or not).

 

[twest42271]

Thanks guys the batteries r brand new

 

[twest42271]

It hasn't always done this and it is just concerning me cause I'm goin hunting for a week I'm leaving Thursday and didn't wanna get stranded in the cold

 

[christopherglenn]

Normal, there are FAR more loads when cold (heaters and plugs) then the stock alternator can provide. When you rev to about 2k the voltage goes up a little right?
You can try plugging the block heater in overnight and see if a warm engine helps.

 

[dmax711]

Mine did the Same thing Last year, new alternator fixed it.