I want to confirm an issue I have. I belive the alternator is shot, I get good volts with no electrical load. turn on the lights, fan-volts drop below 12. Second, on a cold start(all parts are outside temp) the alt will get HOT in under 5min-no load.

Am I correct that it's shot, or do I need to look elsewhere?

 

a good way to test if you have a bad altenator is

with the truck not running take a volt meter read battery voltage should be 11.5 to 12.5 or so

then start the truck test the voltage again should be above 13.5 hopefully

also I believe the PCM controls the output of the alt. so I wouldn't necessarily think you have a bad alt.

although I had 5 total go bad on my old 2500 1 taking out the PCM (awesome)

 

My batt volts (truck off) never dipped below 12v. I tested both independant to rule out a bad batt. With the truck running, at idle the volts were around 13.5-13.8. Once I turn on accesories, fan, lights, ac-the volts drop nice and steady( and quick)

 

well it may be worth trying out a new aly. as NAPA sells them for like 200 or less if i remember correctly it s alot cheaper than a PCM maybe someone else will be of better help

 

I had an alternator failure on the road. See this thread https://www.dieseltruckresource.com/...l-t250893.html

In my case it was the alternator. In your case, if you are seeing 13.5 to 13.8 volts then you are getting some output from the alternator. You might try the test for max output and see what you get. Also when you have the voltage drop, check to see what the output is at the alternator output terminal. You may have some other issue going on.

My batteries were new so I started out with 12.96 volts. After several starts and some driving around I never went below 12 volts. You might do a load test on the batteries. You can take your alternator to AutoZone and have it tested.

 

I replaced the alt and I am lost. At idle the volts will creep down. If I give it a bit of throtle they go up. I feel I have a big power draw as the alt got Real hot under 3min.

My first thought was " what draws lots of power-starter, heater grids. I removed the wire from the batt that feeds the two contactors for grids. No change. I don't think it's the starter as it turns over nice.

The batts were a bit low on volts( 11.4) when I first fired the truck up(had sat at week). If it had a bad cell, or internal short wouldn't the batt die real quick?

 

You changed out the alternator and still have the voltage creep so you have some other problem. If the batteries were at 11.4 at start up what are they now. Have they charged any? During the voltage creep, with some throttle, I would use a meter to check voltage at the alternator output terminal to see if you are still at 13.5 and above. You can also check the alternator feed wire that feeds the batteries. Your alternator may be ok and charging but you are experiencing some other problem. If the output is low then you may have a problem in the field control or PCM.

If your batteries are good they should carry the load for a while before a voltage drop. I would load test your batteries to verify they are good. Also check you battery terminals to make sure they are clean and in good shape.

Maybe some of the expert electrical guru's will chime in.

 

I agree w/ ET RAM. Disconnect both batteries and load test individually. I always load test 2-3 times in a row, letting the tester cool each time. Look for any bulges in the sides of the batteries, or if it seems unusually warm after running the truck. Also, if you can find one, I like using a dial guage type alt. tester. It's about the size of a can of dip with a meter on it, and a little channel on the back you lay on the alt. wire, it'll read amperage output. (They also make one for testing amps at the starter, another nice tool to have) It's never let me down before. That way, you can see what the alt is puttin out while the truck is runnin. And, like already mentioned, trace your alt. wire and check for corrosion and/or a bad connection. It may be puttin out, but not getting all the juice to the batteries.
And keep in mind that a bad battery can eat up a brand new alternator. I've never experienced it, but that's what I've been told. Probably because it's constantly trying to keep up a charge

 

Biododge, FWIW my Greenie does the same thing, been doing it for over a year, no issues.

Other than wondering why it does it and Brownie doesn't, I have gotten used to it.

Where in Illinois are you?

 

I think I got it!!!

Ok. with a fresh approch on things, I started from the begining. I isolated both batts, put the charger on the passenger side-volts went up(took and held a charge). Next, I did the other batt. I started off with 10amp charge, 1/2hr later the amp gauge hadn't moved. So I went to 50amp, gauge showed batt drawing 32amps--- 2hrs later the gauge had not moved.

I am 90% sure this is my heavy current draw I was looking for. So I bought a new batt tonight and install tomarrow. The funny thing is, I had done this first when I started looking for the problem. And at that time the batt did take a charge. However, I only tried 10amp, and charged only afew min. I guess the 50a charge was needed to show the issue.

Thanks everyone for the replys!!!
--patdaly,, I am near Crystal lake..I like the names for the trucks... It wont work for mine though as I think "purplely" sounds funny

 

LOL, Yep, and Barney is out as well.......... You could call it "Purple people pusher" or PPP for short.

At some point we should have enough of us Illinois guys to start a chapter!

 

LOL! Just as I read "PPP" I thought of the song purple people eater! A Il. chapter would be cool--

 

the batt was not it. I took the starter off-cleaned the contacts and wires going to it. Is there a way to test or check that the voltage regulator is working? The fsm only tells you how it works My volts on a meter start at 12.41 and very slowly raise. I dont get to 13v as the alt gets REALLY hot within 2min


I am about to rip my hair out!!!!

 

Bio, look at my response to your post in the help section.

 

Well this is a trip-I took the new alt off and had it tested, it was bad, new out of the box. Now Im back to square 1. Hope this 1 works( or I'll be back to rant).