What would you do with this alternator sit.

[JTucholke]

In diagnosing my battery thermal code I took the truck to Autozone for a battery check. As posted in my other post, the batteries turned out to be great (even though almost 5 years old) but the alternator was only putting out 30 amps.



SO... I priced some reman. alternators and found on at Advanced Auto for $139 with a lifetime warranty and is re-manufactured by Delco (Chebby people rejoice). Put it on last weekend. I then had Advanced check the alternator with their system (different than AZ's).



I've read in other posts that sometimes these testers get confused on our trucks. Well, Advanced told me it didn't look like I was getting a charge with my new alternator. I restarted the truck, ran the test again, and then it did get a charge on my gauge, but it wasn't great with the tester. Weird. He then took my old alternator and tested on the bench only to find out it looked fine. When driving the truck later it looked like I was getting a solid 15 amps from the gauge with the new alternator (batteries were a little low). I'm not sure why the batteries were low, but it could be my old alternator.



One thing I have noticed is sometimes it takes a couple minutes for my gauge to show I'm getting a charge of like 15 amps. Others notice this too?



Now, this isn't a horrible job, but I've already put this one on and it has a lifetime warranty.



Should I put the 5 year old one back on? Any ideas why it takes a couple minutes for a charge to seem to appear?

 

[rscurtis]

IMO, put the old one back on. Alternator output is controlled by the ECM. It is normal for the voltmeter to show a low voltage when the grid heaters are functioning. As you study all the different forums here, you will see the alternators on these trucks are very long lived, but you could be getting near the end on your batteries.

 

[rbattelle]

One thing I have noticed is sometimes it takes a couple minutes for my gauge to show I'm getting a charge of like 15 amps. Others notice this too?

What gauge? Did you install an ammeter? Or are you confused about the factory voltage gauge?



The factory voltage gauge is normally supressed to around 8v during the post-startup heater cycle if the ambient temperature is below 66°F.



Ryan

 

[JLovas]

Its difficult to test alternator output immediately after start up and while the grid heaters are cycling due to the large amperage draw of the grid heaters. This test will show low alternator voltage output. Allow the engine to warm up and test alternator output when grid heaters are not cycling.



I inadvertently left some electrical accessories on in my pickup for a 3-4 day period, drawing down the batteries. The batteries were still able to crank and start the engine, but after about 20 minutes of run time, my volt gauge dropped all the way down to 8 volts and the "check gauges" light came on. Its easy to suspect a faulty alternator, but I wanted to do some more testing, before throwing parts at it. I trinkled charged the batteries up to full charge, and everything was operating as it should. Apparently the ECM has some programming that shuts off alternator output during unusually high and prolonged demands, sort of a duty cycle watch dog.