vinny85

Hi all,
I pulled my alternator ('85) tonight and am going to get it tested tomorrow. I'm not sure if that is my problem, or possibly there can be some other underlying cause for its failure. A little background of what has been happening.
I had the car garaged for about a month or so while I was 'on the road' and after an oil change and some fluid top offs I went to start it and (big surprise) no joy. Nothing -- not even a clicking solenoid or anything. Totally dead. No big deal. I got a jump from my roommate (he has a '90) and I got it started. Shutdown after a few minutes and couldn't restart without a jump. Battery was around 2 years old, so I thought maybe it was a bad battery. Borrowed my roommate's battery for a test, and it seemed to work fine. His battery was also about 2 or 3 years old. Long story short, I drove with his battery for a couple of days until the same symptoms reappeared.
Well, talked myself into possibly another weak battery and bought a brand new one. Worked great for a couple of days until this morning. Shut car off for about 45 minutes and went back out to start - no luck. Nothing. No click from solenoid, starter not even attempting to turn. Voltmeter reads 11.4 or so with a red flag. Ok. Jump it, take the car home, shutdown. Won't restart.
After the first battery problem, I checked circuits through the fuse panel to determine if there may be one that is drawing current (i.e. short) but everything checked fine. Today, I checked the alternator with the car off, ignition ON. Got 12V at BATT output, 12V at Term 2, 2.4 V at Term 1. Jumped car, let it run. had 13.8V on dash voltmeter, 14V output from alternator, 14V across battery terminals.
I did not check the amperage output, I will just take alternator in to NAPA tomorrow. I suspect that the alternator is working, but just not charging battery. My question is this: If the alternator checks OK, what next? Should I be thinking along the lines of fusible links? Or maybe a broken ground? Any advice is greatly appreciated. I'm hopeful that it is just the alternator (more expensive than a bad ground or fusible link, but easier to find!). What is the best way to troubleshoot further to see if I can avoid burning up a new alternator (assuming this one is bad)? Thanks in advance!
Phil

AGENT 86

Its sounds like possible diode problem in alt. If it tests ok, try load test on battery. If thats ok then i guess the search is on for the drain!! Good Luck !! :cheers:

jfb

If the alternator puts 14v across the battery with the engine running, then the alternator is working . When the red battery symbol is lit on your dash, the alternator is not providing current to your electrical system. Your symptom is of excessive leakage current from your battery which discharges the battery overnight. Disconnect the negative cable from your battery and place an ammeter from the battery neg to the neg cable and after the courtesy lights time out, measure the leakage current. It should be smaller than 50 milliamps, my 87 measures 27 ma. If your battery is discharged overnight, you will read leakage current around 3 amps. First check that your underhood lights are off, along with the courtesy lights, vanity mirror lights. If you have any add on electrical equipment, like an audio amplifier, aftermarket car alarm, these items might be the cause of the leakage. While observing the ammeter, pull your fuses one at a time and see if one fuse dramatically drops the leakage current. If it does, than further inspection of the circuits that fuse powers should be performed to find the culprit. Some CFers found their power seat controllers were drawing their excessive leakage current. A defective rectifier diode in the alternator can cause leakage and you can remove the large red wire on the alternator and see if your ammeter drops. Be careful with a wrench on the alternator red wire because it has 12v on it all the time and touching the wrench to ground will cause sparks and will blow the fusible link on this wire. Good luck.


[Modified by jfb, 11:48 AM 5/6/2003]

vinny85

Agent86, jfb. Thanks for the info. I'm headed off to get the alternator tested ...And then I'm gonna do some more investigating. I appreciate the help. I'll post what I find!
Phil

vinny85

Ok, here's my update. NAPA said the alternator is good...which I kinda was expecting since it obviously is outputting enough amperage to run the car and all its electrical components.

I came home reinstalled the alternator, and the car started. All day I have had no problems starting during troubleshooting. Of course I have not driven it anywhere though.

I disconnected the neg battery terminal and hooked up an ammeter to the cable and the terminal. Read 2.49 mA. disconnected alternator - still 2.49 mA. disconnected fuses one at a time with no change. Then disconnected starter now it reads 2.3 mA. I suspect 2.3mA 'leak' is not enough to cause any problems, but on my truck and my roommate's vette the same test yields 0 mA.

I also performed one of the tests from the service manual (can't remember which test it was right now) that involved testing the cranking voltage from pos term to solenoid and then neg terminal to block. The flowchart says if one of them is more than .5V, then check leads. If both of them are below .5V then repair starter (solenoid terminals are bad). So am I to infer that those two voltages should be exactly .5V?

It could be possible that the starter is messed up. But, other than that I haven't found any other source of the 2.3 mA drain. possibly a battery cable change may help?

Anyway thanks again. All advice is appreciated!!!
Phil

lite blue

I rebuilt my '85 alternator three times before I wised up and replaced it with a CS-144. The '84 and '85 alternators were the last of the SI series, and they were seriousely overtaxed. Even with the 120 amp rating, they are just barely hanging on. These mega SIs were only used on those two year Vettes, and the same year Camaros with TPI, and a few Caddys. The CS series came out in '86.
You can easliy retrofit your Vette with a CS-144. Delco has a harness that plugs in between your stock wiring and the newer alternator. I did this about two years ago, and have had no problems, even with underdrive pulleys.
If you want info on specific part numbers for the alternator and the harness, just email me.