Another CUCV Alternator question

[roscoepcoltraine]

Hi all,
Hoping this is not a dumb question that has already been answered. I've read the multiple CUCV Helpful Threads on the CUCV alternators, and although I understand most of it, I'm afraid some of the technical lingo goes beyond my 'shade tree mechanic' level (so, maybe my question is answered somewhere in there, and I'm just not seeing it).

Anyway, here's my situation (which I'm thinking means my Gen1/driver's side alternator is bad):

With key off, I have:
12.4-12.8v at both batteries.
12..4-12.8v at both alternators (with voltmeter leads on alternator big wire terminals).
12.4-12.8v at both small red wires (with voltmeter pos on red wire, voltmeter neg on alternator big wire neg terminal).

With key on, but motor not running, I have:
11.8 v at Gen1/driver's side alternator small brown exciter wire (with voltmeter pos on brown wire, voltmeter neg on alternator big wire neg terminal).
12.4 v at Gen2/passenger side alternator small brown exciter wire (with voltmeter pos on brown wire, voltmeter neg on alternator big wire neg terminal).


So, I'm understanding that the above findings pretty much rule out any problems with the truck's wiring...


With motor running, I have:
11.8v at Gen1/driver's side alternator (with voltmeter leads on alternator big wire terminals). --Clearly, BAD.
14.8v at Gen2/passenger side alternator, (with voltmeter leads on alternator big wire terminals).

I have checked fuse#5 and fuse#12 since they are both related to Gen1 and Gen2, and they are fine.


Here's my question: I'm thinking I need a new/rebuilt Gen1/driver's side alternator -- do you guys agree, or is there something else to check?


And thanks to those of you who created the CUCV Helpful Threads! (Even though I couldn't find the answer to my question there, y'all were helpful in coaching me with the all the diagnostic work above.).

 

[roscoepcoltraine]

By the way, Gen1 belt is tight, with no squeal

 

[87cr250r]

The drop from 12.6 to 11.8 volts when you cycle the key on indicates that battery is bad.

 

[roscoepcoltraine]

Thanks, 87cr250r --
So, that would be my front battery then. So is my Gen1/driver's side alternator also bad, then? (Because if it were good, I would think it would put out 14.8v or so, no?)

 

[87cr250r]

Some voltages to remember:

12.6 volts means the battery is fully charged.

13.6-14.5 volts is the ideal range for an alternator charging.

When cranking the voltage should maintain ~10.5 volts.

Double these numbers for 24v systems.

Your battery raises a red flag because it's showing 12.6 volts (fully charged) but can't carry any load if it dropped to 11.8 with just the ignition on.

Yes, your alternator is likely bad as well. You should replace both the battery and the alternator.

 

[roscoepcoltraine]

Got it, makes sense. Thanks for the education!

 

[sneekyeye]

One thing to be sure of is that your alternator light indicators in the dash are also good. From what I understand, the alternator needs that path to ground and the small load the light provides to turn itself on. If they turn on when the engine is not running but the key is on, then the circuit is good.

 

[roscoepcoltraine]

Yes, I forgot to put in my post what my dash lights look like, sorry.

With key on, but motor off: Gen1 is very weakly lit, and Gen2 is brightly lit.

A few seconds after motor is running: Gen 1 remains weakly lit, and Gen2 goes off.

 

[Tow4]

Hi all,
Hoping this is not a dumb question that has already been answered. I've read the multiple CUCV Helpful Threads on the CUCV alternators, and although I understand most of it, I'm afraid some of the technical lingo goes beyond my 'shade tree mechanic' level (so, maybe my question is answered somewhere in there, and I'm just not seeing it).

Anyway, here's my situation (which I'm thinking means my Gen1/driver's side alternator is bad):

With key off, I have:
12.4-12.8v at both batteries.
12..4-12.8v at both alternators (with voltmeter leads on alternator big wire terminals).
12.4-12.8v at both small red wires (with voltmeter pos on red wire, voltmeter neg on alternator big wire neg terminal).

With key on, but motor not running, I have:
11.8 v at Gen1/driver's side alternator small brown exciter wire (with voltmeter pos on brown wire, voltmeter neg on alternator big wire neg terminal).
12.4 v at Gen2/passenger side alternator small brown exciter wire (with voltmeter pos on brown wire, voltmeter neg on alternator big wire neg terminal).


So, I'm understanding that the above findings pretty much rule out any problems with the truck's wiring...


With motor running, I have:
11.8v at Gen1/driver's side alternator (with voltmeter leads on alternator big wire terminals). --Clearly, BAD.
14.8v at Gen2/passenger side alternator, (with voltmeter leads on alternator big wire terminals).

I have checked fuse#5 and fuse#12 since they are both related to Gen1 and Gen2, and they are fine.


Here's my question: I'm thinking I need a new/rebuilt Gen1/driver's side alternator -- do you guys agree, or is there something else to check?


And thanks to those of you who created the CUCV Helpful Threads! (Even though I couldn't find the answer to my question there, y'all were helpful in coaching me with the all the diagnostic work above.).

Follow the link. Testing the alternator on the vehicle

 

[roscoepcoltraine]

Hi Tow4,
Thank you! Yours was actually the first post I had read (before posting my question), because it seemed to be the exact topic I was needing help with. I think the problem is that I'm an amateur, and so there is some terminology you mention that is above my level (such as B+ and B-, and regulator, and jumper clip -- things I probably should know, but nonetheless didn't know where to find). And, the other thing is -- probably because of my bad eyes -- I couldn't quite figure out in some of your pics where your voltmeter leads were going to. So, I'm sorry that I probably asked a question that you had done a great job of proactively answering in your sticky post. Thank y'all for tolerating the dumb newbie questions that guys like me come at you with

 

[WWRD99]

Hi Tow4,
Thank you! Yours was actually the first post I had read (before posting my question), because it seemed to be the exact topic I was needing help with. I think the problem is that I'm an amateur, and so there is some terminology you mention that is above my level (such as B+ and B-, and regulator, and jumper clip -- things I probably should know, but nonetheless didn't know where to find). And, the other thing is -- probably because of my bad eyes -- I couldn't quite figure out in some of your pics where your voltmeter leads were going to. So, I'm sorry that I probably asked a question that you had done a great job of proactively answering in your sticky post. Thank y'all for tolerating the dumb newbie questions that guys like me come at you with

There's no dumb questions here. You should be able to click any picture and zoom in on. My laptop has the touch pad and use 2 fingers to pinch in and out to get close or far. Not sure what computer your using but it should have that capability. If you can't figure that out post up what computer your using maybe I can help to figure that out too. I'd be curious what you find with the dim light on gen one....they should be the same brightness with the key on. Whenever I do diag like this I start at one end of the circuit that is easiest to get to...the alternator is very easy to get to....check the main ground wire on the back of the alternator and make sure it's solid. A simple push and pull test can find the smallest problem.
I also test after every problem I find to see if it made any difference. Write down voltages on anything you can find on the alternator before you do anything. That gives you a starting point. Most problems can have more that one fix. Not sure what batteries you have but I always charge them separately on a low amp to make sure they are charged plus check the acid as well. I had a pair of batteries fail after doing this but at least I knew they were bad. Batteries are a hefty investment in these trucks so I don't replace them quickly. If you do find the alternator is not charging after going through all the diag rebuilding the one you have is best...there's companies that sell quality kits. Good luck with the truck and hopefully figure it out before this cold snap hits Saturday!!

 

[roscoepcoltraine]

Thanks, WWRD
One of the great things about this site is you guys are so open to educating us guys who know less, but are aspiring to your level.

Good idea on the pinching in and out to zoom -- although I had known about that, my 15 yr old son just now showed me how to do it properly!

Thanks for the reminder on the importance of double checking contacts. My neighbor had helped me clean up all the connections on all both alternators, and we also put dielectric grease on, before I bothered you SS guys with my question. We were both pretty satisfied that the connections were all good. (Also, I was getting the same voltage at the batteries and at the alternator terminals, so my amateur understanding is that that means wires and connections must be good, no?)

And yeah, I was confused about the dim Gen1 too. Since I had gone ahead and bought a new (isolated ground) alternator, I'll be sure to report back on what happens when I install. Its due in the mail in a day or two. I do appreciate your advice on trying to rebuilt the alternator, and I'm all about saving a buck, but I just feel that'd be above my level. Maybe when my Gen2 goes, I'll have upped my level of confidence enough to try rebuilding my own. (I'm a pretty visual learner, so maybe by then somebody will have a YouTube video taking you through rebuilding these alternators.)

Also kind of interesting, I went down to my local Interstate dealer and they tested both my batteries, and they both tested good. To answer your question, they are Group 31 batteries rated for 900-something CCA's new, and each tested above 800 CCA's. (Their brand is OTR.) And yes, you aren't kidding that batteries are a big investment, and even bigger with all this inflation lately. So I was so glad to not have to walk out of there with two new Interstate Group 31 batteries, at more than $200 a pop. (They said they didn't have access to any refurbs currently. I've seen your guys advice about saving some $ on refurbs, if possible.)

So there it is. I'll report back in case that's useful for someone else's learning.
Thank you!

 

[WWRD99]

Re

Thanks, WWRD
One of the great things about this site is you guys are so open to educating us guys who know less, but are aspiring to your level.

Good idea on the pinching in and out to zoom -- although I had known about that, my 15 yr old son just now showed me how to do it properly!

Thanks for the reminder on the importance of double checking contacts. My neighbor had helped me clean up all the connections on all both alternators, and we also put dielectric grease on, before I bothered you SS guys with my question. We were both pretty satisfied that the connections were all good. (Also, I was getting the same voltage at the batteries and at the alternator terminals, so my amateur understanding is that that means wires and connections must be good, no?)

And yeah, I was confused about the dim Gen1 too. Since I had gone ahead and bought a new (isolated ground) alternator, I'll be sure to report back on what happens when I install. Its due in the mail in a day or two. I do appreciate your advice on trying to rebuilt the alternator, and I'm all about saving a buck, but I just feel that'd be above my level. Maybe when my Gen2 goes, I'll have upped my level of confidence enough to try rebuilding my own. (I'm a pretty visual learner, so maybe by then somebody will have a YouTube video taking you through rebuilding these alternators.)

Also kind of interesting, I went down to my local Interstate dealer and they tested both my batteries, and they both tested good. To answer your question, they are Group 31 batteries rated for 900-something CCA's new, and each tested above 800 CCA's. (Their brand is OTR.) And yes, you aren't kidding that batteries are a big investment, and even bigger with all this inflation lately. So I was so glad to not have to walk out of there with two new Interstate Group 31 batteries, at more than $200 a pop. (They said they didn't have access to any refurbs currently. I've seen your guys advice about saving some $ on refurbs, if possible.)

So there it is. I'll report back in case that's useful for someone else's learning.
Thank you!

Rebuilding doesn't save much money at all...I think the kits are 60-70$...once you add in time it's a wash for most. I do mine so I know it's put together correctly and with a solid rebuild kit. The wires that usually give trouble are the grounds...most are cheap crimp with no heat wrap and corrode inside...those are the ones I pull on the most...I've had many that looked fine but pulled apart with little effort...the ground on the alternator back is one I replace even if it looks good. Some trucks are missing grounds!! It never hurts to add some.

 

[roscoepcoltraine]

Some feedback, in case it helps somebody:
Simply replacing my bad driver's side alternator (with a new isolated ground alternator, part# 7847, orig Delco part# 1105500, bought on eBay, $140) solved my problems completely. Gen1 and Gen2 lights now are functioning as they should (equally bright at all times now; going on when key on, going off just after engine starts), each alternator is putting out 14.2+ volts when engine running, each battery is reading 12.6 volts with engine off. So glad I didn't end up having to buy any new $200(!!) Group 31 batteries.
Thanks for all the help, guys!!

 

[WWRD99]

Some feedback, in case it helps somebody:
Simply replacing my bad driver's side alternator (with a new isolated ground alternator, part# 7847, orig Delco part# 1105500, bought on eBay, $140) solved my problems completely. Gen1 and Gen2 lights now are functioning as they should (equally bright at all times now; going on when key on, going off just after engine starts), each alternator is putting out 14.2+ volts when engine running, each battery is reading 12.6 volts with engine off. So glad I didn't end up having to buy any new $200(!!) Group 31 batteries.
Thanks for all the help, guys!!

That's great news! So the low gen 1 light was from the alternator...interesting. Yes batteries are one expensive part for these since they need to be big and high ca...not sure if you're around a military base but there are battery distributors near them that stock the 6tm battery if you can find them. The 31s work fine though since that's what they came from new...they just got replaced with the 6tm since that's what they put in everything. Now look up a rebuild kit and do the spare up!! Would be a fun project.