My car's been down a week now for this mysterious no charging problem. Things have gone downhill alternator wise in this car since the original one died at around 130K, now at 180K and on the 3rd autozone POS that most recently died last week...

I figure, no biggie, I'm used to swaping alternators on this thing at this point, removed the old one (coated in PS fluid of course from recent hose leak) so can't really blame AZ for this one; but I accidentally broke the very fragile red exciter wire; from this point on I've been in LS1 purgatory of having a car that will "run" but can't drive it anywhere.

I bought a soldering iron, bought a new generic 4 pin connector from AZ, cut off the 3 wires I don't need (A, C, D) leave leaving "B" (same location as stock connector) and splice in the new pigtail. I have tested the voltage at the new connector and it's getting 10v when the car is running....(what is it supposed to be reading with the car running to make the alternator charge?) I see conflicting info that it should be 8-9v or 5v......why is mine 10? Short in the wiring harness?

I've tried 3 alternators installing one a night for past 3 nights, no luck, battery goes down to 10v when running.... surely all 3 not duds?? (I know the autozone one is highy questionable junk ) Also I noticed my idiot light for not charging is not coming on....seem a bit odd and makes me think exciter circuit issue? PCM issue? WTH....such a pisser.

None of these worked on the car:
1. AC delco reman stock replacement (tested good on machine)
2. Duralast gold reman (figured it was at least worth a shot to exchange my old PS soaked old one lol...have not had it tested yet on machine)
3. New Carquest 145Amp 03 6.0 truck alternator (not tested on machine yet)


I'm breaking down and driving it down the road to a local shop or maybe even towed to the dreaded and costly stealership very soon unless anyone has any bright ideas?

 

Bump....

The shop has had the car all day, it's the frigging PCM not commanding the alt to turn on....hence the 10v where it should be 5v. Looks like I'm buying a new PCM, which sucks because I spent $400 having it dyno tuned years ago, hopefully they can save the file and put in on the new PCM. Anybody else have a PCM all the sudden stop commanding the alternator? (everything else works fine...except charging idiot light) Seems like a weird problem as I've never experienced any PCM issue; my good ole' LT1 and it's primitive PCM still works like a charm lol...WTH is wrong with LS1 PCMs?

 

The 0411 LSI PCM is every bit as reliable as the primitive LT1 units. I would say your problem is highly unusual, in that I've never run across it in all my years reading this board. In fact, my initial reaction to your shop's diagnosis was skepticism ... I would post up on the PCM Diagnostics forum to see if others have had this problem.

Your tune can certainly be saved and transferred to a new PCM. In fact, I would talk to Steve at "Tuned by Frost" and get your new PCM from him with your tune loaded onto it.

 

Your first problem was throwing away your stock alternator and replacing it with that POS autozone one.

Next time your starter or alternator dies, take it to a starter/alternator rebuilder.

 

The PCM commands the alternator to operate at variable levels in order to save a tiny bit of fuel. In the olden days, there was a voltage regulator that either turned it off or on depending on what was needed. It's pretty easy to change yours to the old style. It will cost you <$10, and you can keep your PCM.

http://www.racingtheexocet.com/?page_id=348 Look towards the bottom of the page.

 

Steal the 5v from somewhere else and feed it into the turn on wire for the alternator. Ive done it before in a pinch (all the sensors run off 5v signals from the pcm). Do not feed it 12v+ however.

 

I dont think that info is correct. I think the pcm just sends a constant 5v and thats it.

 

6 days, $876 shop bill (including 1 brand NEW PCM) later it's FINALLY charging the god damned battery with the AC delco alt I already bought.

FWIW the shop tried the resistor "trick" to provide 5v to the alt L terminal and it did not work....apparently LS alternators run on some sort of voodoo black magic supplied by the PCM I can't possibly hope to understand or comprehend. At least I now have a truck alternator and a highly questionable duralast POS on hand should the new AC delco fail....

What a cluster f#@k!

I need a drink or 10 after dealing with this nonsense for over a week....

 

Very odd issue to have (random PCM failure like that.) I wonder what the order of events was here, meaning did that last alternator actually die or was it a PCM failure all along? Or did the PCM and alternator coincidentally experience failure, and/or did the PCM fail after the last alternator died, perhaps due to some sort of short/spike when the exciter wire broke and/or during the wiring repair?

 

Honestly... my real opinion on this is that the A/C Delco Alternator is what really fixed the issue. Do a search on my threads, I replaced over 5 Autozone Alternators in the course of 1 year.. all BRAND NEW non reman DURALAST GOLD.. they are absolute junk and most members who have used this on this forum experienced the same issues you did with them dieing. I switched to Powermaster and havent had an issue since.

The reason I don't believe that you ever had an issue with your exciter wire or PCM is that after replacing with another Autozone alternator, it DID work for a short time before dieing, just long enough for the alternator to crap out. If there was an exciter wire issue you wouldn't get 5 miles from your driveway.

 

I KNOW THIS POST IS OLD

so guys im having sort of the samei ssue. if i jump the exciter wire up by the pcm with a 5v source my alt will work just fine. so figuring it was the pcm i picked up a new one and it still wont chargev unless i jump the exciter wire.. Now ive eliminated any chance of breaks in the wire between alt and pcm. is there anything else that controls the exciter wire besides the pcm??? thanks guys.. fyi its a autozone alternator but if my alt is charging when i jump the exciter wire doesnf that eliminate it being an alt issue?

 

Absolutely incorrect. 5v applied to the correct terminal WILL turn the voltage regulator on in the alternator. The shop performed this incorrectly or gave you bad info. See below.

Its a computer only circuit. Im not sure WHAT makes the pcm turn that wire on, like what requirements have to be met. What is your voltage at the alt with the engine running? Zero? Next I would check it AT the PCM and see the difference. If two PCMs dont work in your car, I would try and figure out what makes this wire excite, maybe rpm based? All fuses good in the car? And you can grab 5v from the MAF or other sensor to get you by in a bind. I have one running like this for 5+ years though there is no MAF in the car.

 

So it seems that one could just put together a few resistors (from 12v) and built a voltage divider into a 7805 - 5 volt voltage regulator and call it good.

 

gonna check to see bout volts at the alternator running.. i know my gauge just reads roughly 12v. ALL fuses are good i could use another 5v source like i been doing its just i want to figure out y my alternator wont get signal from the exciter wire from the pcm. i know theres no breaks in the wire up to the pcm... The computer has to get a signal from somewhere to apply power to that wire.. i guess il have to do some more searching..