Technical Newbie with a Bad Alternator ????

[better2diy]

Have a 1981 Pininfarina Spider. Alternator was not charging and had it rebuilt at a local shop specializing in this work. Now there is severe engine surging, but runs fine when the leads are disconnected from the alt. and clamped together. Returned the alt. to the shop to be tested. Wife picked it up with a report it is working fine. Reinstalled it, see the same symptoms. Have the appropriate wire diagram and can only conclude that the alt. is indeed bad. Any suggestions would be appreciated. THANKS

 

[GeorgeT]

Is this a carb engine or fuel injected engine?

 

[better2diy]

The engine is fuel injected. Also, just had he alt. tested by the rebuild shop, it's AOK. Installed it and the surging was there for 2-3min. and it smoothed out and idled fine. Ran it for 10min., turned it off, restarted and the disease was immediately present and didn't go away. Any suggestions would be appreciated.

 

[jconfar]

might be a dumb suggestion but have you checked your grounds? I just re-wired my '70 to have a single, solid ground point and my electrical issues went away immediately... I can even drive it at night now that the headlights are brighter than a flashlight!!

 

[better2diy]

Hey Jason, Thanks for your thoughts. Yup, grounds were checked early on. Also I think they are OK because everything runs normal when the alt. is disconnected. The wizards at the rebuild shop think it's an alt. problem and are in process of giving it another rebuild to replace all parts again. I'll post with the outcome.
Bill

 

[GeorgeT]

This may be a silly question but is the polarity of the alternator correct and is the voltage output of the alternator correct?

 

[better2diy]

Rebuild shop replaced all components for the 2nd time and again reports it tests out OK. I put it in the Spider and the disease is still there (rhythmic idle swinging between 550 and 750 rpm, idles fine when alt is disconnected, with good voltage output at 14v). SO, with alt disconnected, I disconnected both battery cables and jumpered them to my truck, thinking that the Spider would be talking to the truck alt. Car started and idled fine. Any opinions as to if this is conformation that rebuilt alt. is indeed NG?? Regarding the polarity suggestion from GeorgeT, i would think that it would be a basic issue during the rebuild, but how should I check it out? Thanks to all responders for your replies. Bill P

 

[GeorgeT]

Try one more thing: Disconnect the battery, jumper the battery cables to your truck battery and start your car (do not start your truck). Does it idle okay or is it erratic? If it is okay, your battery may have a bad cell - I had this problem in a carbed Spider - erratic gauges and idle.

 

[better2diy]

After 5 days of hunting in a remote area of NY Adirondack Mts., I'm back to civilization. (Got a 175 lb, 8 point white-tail). Had ordered a new alt. It arrived while I was away, installed it this PM, problem still there. What a wild suggestion by GeorgeT above. Will try a different bat. in the AM.

 

[better2diy]

GeorgeT, you are the man! I connected a new bat. this AM and the problem is gone. (By the way, I also wrote your name after "wizard" in my dictionary). Who would have thunk that the new battery I was using could be defective!! I have had some strange electrical issues eventually traced to a battery problem, but this idle problem skunked me due to my innate assumption that a new bat. would have no defects. Thank you