Alternator Question
 

Hi,

The other day, I noticed the battery light come on on my 95 993, I gave it some throttle and it went away.. so i thought it was just a glitch. Later on that day, the light came on again, but as i revved the engine the battery light became dimmer... Pretty soon, other random lights started coming on. I knew I was running on the battery juice alone, so I drove home with the headlights off. The second I got home the car totally shut off.
Do you think its just a bad belt?
BTW: I noticed this problem after taking her to a carwash (thats probably a mistake with these cars)

Check grounds, voltage regulator possibly alternator. Doubt the car wash had any thing to do with it. Good luck, Tim

Given the level of engineering in the wiring harness it's unlikely this problem originated with the car wash. The spiderwebs in your clear coat, that's a different story.

All right, so is this an occasional use car? My guess is, if you're like me and eleven million other people around here, you take public transportation on a daily basis and the car sits. A 993 sits, with all of the parasite current drain ticking away, the battery slowly fading.

Let's suppose further that you park this car in a public indoor garage. Ok, so the battery drains between starts. Then the garage attendant starts it up and immediately gives it full throttle to bring it to the front. Think about that from the perspective of the alternator.

The battery drains down probably 20% when the car is not frequently used. Now the car starts, and the alternator immediately goes to full-field in an attempt to bring the battery condition back to 100%. This takes a while, particularly with the engine at low RPM. So the alternator gets very, very hot, and all that heat is the enemy of electrical components, cooking the diode plate.

Happens all the time and is the reason why my daily driver needed the alternator replaced at 60,000 miles.

So first things first. Can you charge the battery for THREE DAYS nonstop using a chipped battery maintainer like the Battery Tender Junior? All electrical diagnosis begins with a fully charged battery.

Next: with the battery fully charged for THREE DAYS, what is the battery voltage measured at the battery with the ignition off? What is it with the engine running?

Those two values are the key to making any progress here.

How old is the battery? If it's older than five years, that's the problem right there. You get three to five for battery, right? :)

There's a whole decision tree to follow but the above steps are the critical ones to getting on the right path.

Now if on the other hand you tell me that you commute to New Jersey every day with the car, that's a different story . . .:)

Appreciate the response...Actually, I dont think the battery is the culprit. It was freshly charged with an automatic battery charger. And I actually just ordered a trickle charger so I'll always have a fully charged battery.. My mechanic looked at it today, and said its the alternator..I need a new clutch, so everything has to come out, engine and all...so he's gonna do the alternator at the same time.. Any thoughts on what to change while the engine is out? She has over 100k miles.

Check voltage after fully charging the battery. Should be at least 12.5 at rest, 13+ at idle and no more then 14.2 at 2500 rpms.

As I suggested in another thread, check for oil leaks on top of the engine, degrease engine and trans.

New hydraulic valve lifters. Possibly new plug cables? New belt for the twin distributor. New belt for the PS pump. New clutch slave cylinder. Change transmission oil.