Engine/Transmission (1994 - 1998) Voltage and RPM fluctuation when engine cold

[rstl99trial]

I noticed when I started my truck at the cottage yesterday morning (temperature had dropped and there was frost on the ground), it kind of balked, as if there was barely sufficient voltage to turn it over. It started right away though. After starting, I noticed the voltmeter read low (first line above the 8), and only some seconds later it went up to above 14, where it usually sits. Drove back to the city, all seemed fine.



This morning, when I started it, it didn't balk like yesterday, but similar thing with the voltmeter (low at first then goes up to 14). In addition, I notice now, when the truck is idling cold, that the voltage cycles from 14, down to a lower spot for a few seconds, back up to 14 for more seconds, then down again). I notice the engine rpm goes down when the voltage drops, and comes back up when it rises to normal level.



What could be happening?

 

[FourBarR]

grid heaters cycling on off. more pronounced in cold weather. How are your batteries? If your batteries are old I would get them load tested.

 

[rstl99trial]

grid heaters cycling on off. more pronounced in cold weather. How are your batteries? If your batteries are old I would get them load tested.

Thanks! Still relatively new to Cummins, and hadn't operated my recently acquired '96 in cold weather yet. Makes sense, that's probably what's happening. I gather the grid heater circuit is operated by the Computer based on an engine temperature sensor, meaning that once temperature X is attained, the cycling stops?



The batteries are mis-matched on the truck and one is notably older than the other one. I'll be putting the truck away for the winter (I bought it to carry a slide-in camper during spring-summer-fall trips), and my plan is to put 2 new batteries in there in the Spring (along with 5 new tires) before heading out on lengthy trips.

 

[The patriot]

IIRC under 59 F they'll cycle.

 

[cerberusiam]

I gather the grid heater circuit is operated by the Computer based on an engine temperature sensor, meaning that once temperature X is attained, the cycling stops?

Timed cycle based on the intake air temp. The colder it is the longer they will cycle to get combustion temps up.

 

[MLee]

And while cycling, when you drive off and reach 18 miles per hr, it stops cycling. This is normal for the Cummins family.

 

[DieselDoghouse]

They will cycle until:



Intake air sensor >59°F

Road speed >18 mph

Engine speed below 1800 rpm.



BTW if you're new to cummins welcome! If it gets REALLY cold you may want to cycle the key twice (turn to wait to start... light extinguished... turn key off and REPEAT, start truck).

 

[DieselDoghouse]

WHOOPS! meant to say engine speed >1800 rpm. Dang keyboard in my bwain!!!

 

[rstl99trial]

WHOOPS! meant to say engine speed >1800 rpm. Dang keyboard in my bwain!!!

Yeah I figured that's what you meant!

Indeed, I'm finding out a lot about these Cummins engines, and so far it's all good.

Addressed the KDP after getting it, and the pin hadn't moved at all. Oh well, at least it's done now and has new seal on the crank and cover...

I paid for an oil change and fuel filter change, but will have to have a go at it myself next time. Seems a bit cramped access to do those jobs though...

 

[RVPILOT]

alternator

After many miles on the clock iv'e experienced about everything that could go wrong with the cummins except a rebuild. I think your alternator needs replacing or the brushes, which is much cheaper. they last about 200 to 250

thousand. Batteries should be the same age. with a mismatch the weaker one will bring down the newer. I found this out the hard way, I kept going back for a replacement under warranty until both batteries were replaced with new and since then no more trouble.