Topic: Help me with my altenator woes...

[TahoeYJ]

So last Tuesday my alternator took a sh!t on me. So being the cheap thinker I am, I figured I could snatch the one off my old motor and be good to go. It was only like 1.5-2 years old when I pulled the engine. Put it in, bam my volt meter is reading 14. So Saturday night this one acts up... I pull it out Sunday morning, run it to Kragen to have it tested, and it tested OK. Maybe when I dropped it while walking with it to my neighbors house to borrow his car, it knocked the brushes or w/e loose?  But it tested OK. Everything was fine when I put it back in...

So today it was reading 12 volts again, now it shows nada. I checked the connections, checked the fuse in the main fuse box, etc but all seems well. Is it possible that this alternator went bad while sitting? I've pulled this one and I'm going to take the two into Kragen and have them tested, if they end up failing I'm just going to upgrade to a higher amp unit... But in the mean time, is there anything I could be overlooking??? Every wire has been checked and checked and then checked once more, but I can't see anything wrong 

I want this outta my hair... I seeeeeriously don't want to chase a %^*&ing electrical problem down...

[Jeffy]

Hmm, don't have a spare PCM do you?

[TahoeYJ]

Hmm, don't have a spare PCM do you?

I do, off my old motor  tried offing it before but noone bought it. What would it have to do with the charging issue? I guess if both units test good then swap the brain?

[sharpxmen]

I do, off my old motor  tried offing it before but noone bought it. What would it have to do with the charging issue? I guess if both units test good then swap the brain?

the alternator charging field is driven by the PCM - not that common of a problem but there was another member that end up replacing the PCM and the alt start working again.

[Sine Deviance]

The voltage regulator is on the PCM. If your Jeep has suddenly started eating alternators or will not charge even though your fuses are good and your alternator is good, a new PCM is in your future. Sorry I have to be the bearer of bad news.

the alternator charging field is driven by the PCM - not that common of a problem but there was another member that end up replacing the PCM and the alt start working again.

Yep, that was me.

[TahoeYJ]

Both tested fine and swapping the PCM changed nothing, so today I started farting with the electrical with my dad and neighbor. We weren't getting voltage from the wires that my neighbor said "excite" the alt. His Camaro was showing 8.? volts with the key on, mine showed none. So somewhere along the line I've got a short in the wire or something else is loose somewhere...
I'm done with it for the day, it's dark. I'm gonna fiddle with it again tomorrow

[sharpxmen]

Both tested fine and swapping the PCM changed nothing, so today I started farting with the electrical with my dad and neighbor. We weren't getting voltage from the wires that my neighbor said "excite" the alt. His Camaro was showing 8.? volts with the key on, mine showed none. So somewhere along the line I've got a short in the wire or something else is loose somewhere...
I'm done with it for the day, it's dark. I'm gonna fiddle with it again tomorrow

you won't be getting any voltage with just the key on, the motor has to run first. measure it with the wire plugged in.

[Sine Deviance]

Both tested fine and swapping the PCM changed nothing, so today I started farting with the electrical with my dad and neighbor. We weren't getting voltage from the wires that my neighbor said "excite" the alt. His Camaro was showing 8.? volts with the key on, mine showed none. So somewhere along the line I've got a short in the wire or something else is loose somewhere...
I'm done with it for the day, it's dark. I'm gonna fiddle with it again tomorrow

you won't be getting any voltage with just the key on, the motor has to run first. measure it with the wire plugged in.

Actually you don't have to test the line at all. Just crank up the Jeep with the new PCM and a known good alternator installed and watch the voltage gauge on the dash. It should read in at least the 14v range if the system is charging properly, otherwise it'll read 12v or less and you're back to square one. This should take effect as soon as you crank up the Jeep, i.e. there's no delay. Also, if your battery is low it'll read higher, so don't freak out, this is normal. After swapping my PCM my voltage gauge was reading in the 16v range until it had charged for a bit. Normal charging voltage with a near-full battery is 14.4v by the way. I'm willing to bet the new PCM will fix the problem.

[TahoeYJ]

So after thinking all day and discussing it with my dad, we decided I should have the alternators tested by another shop that rebuilds alt's and starters. Both tested good, but the guy wanted to open them up and see how they looked inside. The brushes on one were completely gone, and the other was so worn that it was skipping over the rod inside. He said he's seen this same situation before where they test OK on the machine but don't charge on the car. It was $100 for him to rebuild it, $115 w/ like a $70 core charge for a new one at Kragen... I started talking to him about upgrading to a higher amp unit and he right away spotted a 135A unit. At first he said it'd be expensive since I didn't have a matching core, but then he said he'd go ahead and take both of mine as a core and gave me the 135A alternator for $120  Not knowing if it would solve my problem or not, I brought it home anyway.

The verdict: It charges!!!  Even with the fan running, stereo and heater blasting, and headlights on the battery shows 14.24 volts and the voltage gauge shows 14 volts. I've gone for about a 30 minute drive and all seems well.

Funny thing was that even though the 135A is larger, it was actually easier to slide in place? 

[Jeffy]

Congrats.  Not too many alt. rebuilder's anymore.

[Mozman68]

Almost makes me wish mine didn't come with the 117amp...not worth updating it until it takes a complete crap.

[TahoeYJ]

What puzzles me is that even though both tested good even with a load on them, they still didn't work on my Jeep... Either way, I'm just happy to have it fixed. I was thinking I was going to have to fight some stupid electrical issue which was the last thing I wanted to do. And what's even better is that I got 50% more power for only $5 more  I think 135 amps is more than enough for an e-fan, stereo, and eventually a winch. And if it's not, upgrade aga\in 

[neale_rs]

Great deal you got there!