Mike Murphy

It's been -1F up to low 20's in Chicago lately...

I was taking my car to get a hand car wash and the engine started running rough. In fact, it continued to get worse, even backfiring as I tried to give it some gas. It finally died and when I tried to start it back up, it wouldn't even crank - it was as if the battery was dead. The battery is 6 months old.

One of the workers offered to jump start it with one of those portable battery starters, and that seemed to work. I instinctively turned off the heaters, headlights, fresh air and rear/mirror defrosters. I got home just fine.

But before I shut the engine off, when parked in my parking spot, I turned on everything: brights, driving lights, heaters full blast, fresh air, defroster, etc. The engine started running rough again, so I knew right away that the engine was having trouble due to proper battery voltage/current supply.

I removed the battery and slow-charged it for 2 days (2amps or less). It was reading 13.5 volts on 100% charge. After reinstalling it in the car, I tested the
drain with a mulitmeter: 80-85mA. Sounds fine to me.

I started the car and did not see a voltage increase, but when I revved the engine up to 2500 RPM, I instantly got 14.7 volts. So the alternator isn't kicking in right away. I re-tested this numerous times, and sure enough, the alternator doesn't charge until it gets at least 2500 RPM. Then it works fine, produces 14+ volts, even at idle. It's just that getting it to "excite" is the problem.

I shut the car off and now the heater motors are continuing to run, even with the key out of the ignition and the switches off! There, I just found the source of my battery drain!

Now for the questions:

1.) Is the alternator charging issue normal? Actually, from what I recall from my auto-education, this is the voltage regulator not "exciting," correct? The alternator was rebuilt in 2003.

2.) Is the heater issue the relay or some other temperature switch issue? Again, I think the fan will come on if the engine bay gets too hot, so maybe that is faulty? Or is that temp sensor built into the relay?

3.) I hate that relay anyway, is there a way to just by pass it? I know of the heater mod that shunts the internals so that you can run the footwells without the rear compartment fan, but I don't even want that stupid relay at all. I'd rather just use the switches when I want to turn on and off the heat.

Finally, I should also note that my driver side window just came off its track. I probably shouldn't have tried to open it with the freezing water from the car wash causing it to stick.

I even had trouble opening the door to the gas tank because of the frozen water.

Man, not a good day for the Porsche!

theiceman

That could be why mine is sleeping ....
definitely sounds like the alternator/regulator.. I think yours is internal so the whole thing has to come out anyway. Of course check to see if the belt is not loose and slipping first. strange that the light would not come on though. Does it come on with just the ignition . Tht would tell you if the light is working. I have a Volt meter in my car and whenever I start it afte sitting for a whil it immediately goes to about 14.5 or so , afte a few minutes of driving it goes back down to about 13.5 ..after it has "topped up " the battery.
The dying of course due to the facy the battery is running the engine and when you turn off the accessories you have enough pwer to supply spark. Turn on the accs and you have now depleted your energy in your battery and you don't have enough left to charge the coil. YOu ain't putting enough out of your alternator to run the car.

Sorry I can't comment on the rest I have an " archaic" 78 .. no fancy gizmos :-)

Mike Murphy

Actually, my alternator light doesn't work. That's probably why I'm in this mess. I really need to get that fixed, but I haven't been able to pull the gauge out.

theiceman

Well now is a good time since you may be off the road for a while while you fix your alt/reg. If you can get any of the guages out ( they are press fit in ) pull it then reach in with your hand and work the others out. Alternatively pop the hood and reach through from the front luggage comaprtment after removing a few bits and push it out . then you should be able to replace the bulb. Without a voltmeter in these cars electrical issues can be tricky to troubleshoot. Without an alternator bulb .. well..... your pretty well doomed :-)
I think Porsche certainly missed the boat on this one. I would certainly like a VM over a clock any day. I always thought it odd that a car company whos history is racing and performance would forgoe waht I would consider a critical guage and give you a big whopping clock that could be integrated into the radio anyway .....

anyway I think you are on your way to recovery.

Mike Murphy

Thanks, IceMan. Yes, I am used to having voltage and an ammeter gauge in my cars as well.

Mike Murphy

IceMan, I just thought of something neat. I don't smoke or use the cigarette lighter. Wouldn't it be cool to have a voltage gauge that plugs right into that cigarette lighter socket?

ron mcatee

I saw one at a parts store the other day. Cost was around $20. Just plugs into the cigarette hole.

Mike Murphy

I just found one online too: http://www.cetsolar.com/cigplugs.htm

Mike Murphy

I have to rev my engine up to 2500 RPM before the alternator light goes off. Anybody else have this problem? Is the an issue with the alternator or voltage regulator?

1988 Carrera 3.2

PorscheMD

The alternator light has to work in order for the alternator to charge! This is critical for your car to charge properly! When you turn the key on and engine off, the light should come on. This is a bulb check. If you check the voltage at the bulb socket, you will have ground at the blue wire coming from the alt and batt. voltage at the red/black wire. When the car starts the alt energizes the blue wire and you should have at least batt. voltage at both the red/black and the blue wire. This is how the light goes out once the car is running. The current has to run through the bulb. If the bulb is bad the alt won't charge!

Mike Murphy

When you say "the current has to run through the bulb," I don't understand how this is practical. These car have 90-amp alternators. I know of every few light bulbs that can pass that kind of current. How does this work exactly?

PorscheMD

Ok, Probably a poor choice of words on my part. Because, the bulb has to be good for the Alt. to charge properly, over the years as a reminder I have always told myself the the current has to pass through the filament and if it can't the alt. won't charge. It is my way of keeping things in my memory. What actually happens is this. The blue wire has to have a certain amount of resistance to make the alternator start charging when the engine is running. The bulb supplies this resistance. If the bulb is burned out the blue wire cannot excite and the alt will not charge properly. On some early 911's sometimes you have to add a resistor to the blue wire to make the alt charge and turn the light out completely.

Mike Murphy

OK, I see. Very interesting, actually. I wish Porsche just used a gauge instead of the idiot light. OK, I will check and replace the bulb.

glenncof

Look at the circuit diagram of the alternator and ALT light. That tells you what is going on. Current only flows in the direction of the arrow in a diode.

Also when the light is NOT Lit, there's no substantial current going thru it.

Quiz, who can tell me why the light goes on 'almost' immediate after shutting ignition while the engine runs down ? (two part q. why 'on' at all ? why not immediate?)

PorscheMD

Well, While the engine is running you have batt voltage to both sides of the bulb. When you turn the key off, you lose power to the bulb on the side that is not coming from the alt while you still have power on the blue wire coming from the alt to the bulb until the alt quits spinning so the light lights momentarily. I think this is the "why on at all part". As far as the "why not immediate" part, I would say it is pretty much immediate.