Bizarre electrical problem with 80SC
09-23-2002, 11:29 AM
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Bizarre electrical problem with 80SC
Had charging system problems a few weeks ago. The car would die while driving short trips in the city, battery was totally dead. The charging system was tested, alternator putting out 80 amps at 13 volt under full load. The battery could not consistently hold a charge after being loaded. It was replaced and everything was all right until the past weekend.
Took a 4 hour trip on Saturday, no problems.
Sunday drove with a fair amount of electrical stuff turned on; stereo, headlights, wipers. After an hour it seemed like the stereo wasn't getting enough power. I turned it off along with the headlights and wipers so the only thing drawing power was for the engine. After another half an hour the engine died. Battery was dead, I was able to crank the engine but very slowly. During the trip the car was running at around 3500rpm, this should have been plenty of revs for the alternator to charge the battery.
This is the bizarre part:
After sitting for half an hour, tried to start the car and it ran fine. Started it 3 or 4 times just to test the capacity of the battery. Everything seemed fine even with all stereo and lights on. Drove the remaining 2 1/2 hours home and no problems.
My best guess of the problem is: an intermittently working alternator, a problem with the new battery, an intermittent short that is drawing on the alternator and battery.
When my mechanic checks the charging system he probably wont find anything wrong. Now I'm afraid to take the car very far for the fear of being stranded.
Any suggestions, no matter how obscure, are greatly appreciated.
Mark
Took a 4 hour trip on Saturday, no problems.
Sunday drove with a fair amount of electrical stuff turned on; stereo, headlights, wipers. After an hour it seemed like the stereo wasn't getting enough power. I turned it off along with the headlights and wipers so the only thing drawing power was for the engine. After another half an hour the engine died. Battery was dead, I was able to crank the engine but very slowly. During the trip the car was running at around 3500rpm, this should have been plenty of revs for the alternator to charge the battery.
This is the bizarre part:
After sitting for half an hour, tried to start the car and it ran fine. Started it 3 or 4 times just to test the capacity of the battery. Everything seemed fine even with all stereo and lights on. Drove the remaining 2 1/2 hours home and no problems.
My best guess of the problem is: an intermittently working alternator, a problem with the new battery, an intermittent short that is drawing on the alternator and battery.
When my mechanic checks the charging system he probably wont find anything wrong. Now I'm afraid to take the car very far for the fear of being stranded.
Any suggestions, no matter how obscure, are greatly appreciated.
Mark
09-23-2002, 11:39 AM
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My guess is an intermittant regulator or intermittant wiring connections to/from the charging system. On a car that's 22 years old it's not uncommon for wiring connectors to get corroded. You said that it started fine after waiting half an hour - sometimes this can happen since a battery under no load somewhat recharges itself a little. Best of success to you!
Chris
Chris
09-23-2002, 12:43 PM
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Alternator may be failing, probably drops current when it gets hot. Battery failure was probably due to alternator going out after use.
If you haven't upgraded already, this may be the time and a good excuse to put in the Alternator w/ built in regulator.
Possibly the regulator, but when that goes it usually locks open and cooks the battery, in the meantime your lights go dimmer and brighter with RPM. Did your battery look like it was boiling over?
rjp
If you haven't upgraded already, this may be the time and a good excuse to put in the Alternator w/ built in regulator.
Possibly the regulator, but when that goes it usually locks open and cooks the battery, in the meantime your lights go dimmer and brighter with RPM. Did your battery look like it was boiling over?
rjp
09-23-2002, 03:09 PM
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Symptoms: The car ran fine for a while, stereo faded, all electricals were shut down, engine finally died. Cranked very slowly but wouldn't start. 30 min later, starts fine (3 or 4 times), runs fine for the 2 1/2 hr trip home.
Check all the grounds and other connections! If the engine actually died while driving as you stated, it was probably because there was not enough voltage/current available to the ignition and/or fuel pump. That doesn't necessarily mean that the battery was actually dead - it may have just been temporarily "out of the loop". After all, it had enough juice for 3-4 starts after 30 minutes of "rest". I doubt that the battery "magically" re-charged itself enough for 3-4 starts during the 30 minutes that the car wasn't running. I'd certainly check all the ground (and other) connections - they may be going bad when things get hot and recovering as the car cools. Slow (or no) starter action when hot is a classic symptom of a bad ground strap or maybe a dying starter).
At they keep telling me:
When in doubt, check the grounds.
That said - You may well have a bad alternator or regulator - every time I've checked the voltage on a properly functioning alternator, they've shown 14.5 - 15.5 volts. A reading of 13 volts (as stated in your post) is essentially equal to the nominal 12 volt battery voltage - it's never going to get charged at that rate.
Best of luck, electrical gremlins can be nasty.
Check all the grounds and other connections! If the engine actually died while driving as you stated, it was probably because there was not enough voltage/current available to the ignition and/or fuel pump. That doesn't necessarily mean that the battery was actually dead - it may have just been temporarily "out of the loop". After all, it had enough juice for 3-4 starts after 30 minutes of "rest". I doubt that the battery "magically" re-charged itself enough for 3-4 starts during the 30 minutes that the car wasn't running. I'd certainly check all the ground (and other) connections - they may be going bad when things get hot and recovering as the car cools. Slow (or no) starter action when hot is a classic symptom of a bad ground strap or maybe a dying starter).
At they keep telling me:
When in doubt, check the grounds.
That said - You may well have a bad alternator or regulator - every time I've checked the voltage on a properly functioning alternator, they've shown 14.5 - 15.5 volts. A reading of 13 volts (as stated in your post) is essentially equal to the nominal 12 volt battery voltage - it's never going to get charged at that rate.
Best of luck, electrical gremlins can be nasty.
09-23-2002, 03:39 PM
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[quote]<strong>If you haven't upgraded already, this may be the time and a good excuse to put in the Alternator w/ built in regulator</strong><hr></blockquote>
You may find that if you need to replace your alternator, if you don't have it rebuilt, that you can only buy an altenator with the built in regulator (don't remember if the Bosch-based alternator made in Australia has an integrated regulator or not). If you do decide to "upgrade", there's an article in the PCNA 1974-1989 911 Parts and Technical Reference guide on how to do the conversion (it was also a dealer bulletin years back). Note it says you need to replace the air guide on the back of the alternator, and they are NLA. All you need to do is file or Dremel part of your existing air guide to make room for the integrated regulator.
You may find that if you need to replace your alternator, if you don't have it rebuilt, that you can only buy an altenator with the built in regulator (don't remember if the Bosch-based alternator made in Australia has an integrated regulator or not). If you do decide to "upgrade", there's an article in the PCNA 1974-1989 911 Parts and Technical Reference guide on how to do the conversion (it was also a dealer bulletin years back). Note it says you need to replace the air guide on the back of the alternator, and they are NLA. All you need to do is file or Dremel part of your existing air guide to make room for the integrated regulator.