Engine/Transmission (1998.5 - 2002) Do I have an alternator problem ?

[Tractorat]

I actually noticed this a while ago, and forgot about it. When I first start my truck, and it doesnt matter if it warm and just running, the alternator looks like it is discharging. When I first turn the key on, it shows about 14v. After about 15 or 20 seconds, it comes back up to the 14 volts. I forgot about it for a while because I thought it could be related to the batteries. But, I put brand new batteries in it today, and it is still behaving the same way.



Thanks,

TRat

 

[DAWG-1]

When the grid heaters cycle everytime you start the truck for approximately 90 seconds they will draw down the volt gauge just like you experienced. If you have a DC amp gauge you can see how much the alternator is charging.

What happened to the old batteries ? Sam.

 

[Tractorat]

I took the old batteries back for the core charge.

The grid heaters shouldnt have come on, since the truck was warm. How would I test to see if they are coming on anyway ?

 

[Tractorat]

BTW, the old batteries were the original OEM's. They were new in Sept 01 when I bought the truck. They were still fine, but since they are now 9 years old, I didnt want to have a problem at the worst possible time.

 

[Ramtuf1]

It doesn't always matter that the truck is warm. It also depends on the ambient temperature outside as to if they cycle. I have seen my truck at operating temperature cycle the heaters at restart quite often.

 

[Tractorat]

Well, its about 45 degrees outside. Is that cold enough to have them go on ?

 

[JMetzger]

My 02 has done that since new, doesn't seem to make any difference if it is warm or cold & I know the grid heaters do it to. Someone told me that either the ECM or PCM controls when the charging starts.

 

[Tractorat]

Thanks,

Im sure mine has done that since new. But, I never look at the alternator when it first starts. Oil pressure (and fuel), but I just zone out on the alternator at least for a few minutes.

 

[JLandry]

Well, its about 45 degrees outside. Is that cold enough to have them go on ?

Absolutely!

 

[DAWG-1]

Hi Tractorat,

If you have a multi meter you can check at the relay. See if the relay is getting a 12 volt signal at one of the two smaller wires ( 1 is ground and 1 is a 12v signal wire). If the relay signal wire has 12v, then check to see that the larger diameter wire going to the grid heater is 12v. As you have seen from your Volt gauge the voltage will be above 14v when there is no large draw and below when there is. Sam

 

[PBJ2500CTD]

TRat,
IIRC the grid heaters can come on up to 60* ambient temp. It is a two stage event with the cycle and time dependent on the ambient/intake temp. The grid heaters shut down when the vehicle reaches ~ 15 MPH. With each grid sucking up ~95 amps each (95 X 2 = 190 amps) you will see the cycling on the voltmeter. I can't seem to locate my operation information and am relying on my flickering memory cell.