Alternator issue?

[maclaren65]

I am starting to think my alternator might be on the way out.

Last night after driving my 87 Carrera for about 30+ minutes, I turned it off for about 5 minutes. Then when I started it up and began to drive away I tried turn on the headlights again and they wouldn't work and there was a scraping noise coming from the back of the car. I turned off the car and inspected the engine compartment and didn't notice anything. Then I restarted the car and the noise wasn't present and the headlights turned on fine.

Do alternators usually fail and stop working immediately or is it a progressive failure? I had been using my Garmin GPS for a couple hours off and on. It was plugged into the cigarette lighter socket, so that was drawing power too.

Any ideas?

Thanks,

Richard

p.s. I just bought this car yesterday.

[flat6pilot]

Generally speaking, electrical components either work or they don't (electronics are digital in nature, either on or off).

However, in the case of an alternator there is at least one analog variable: brushes. The brushes will wear overtime and COULD cause the output to get worse until it finally "dies". This is just one of many failure scenarios and could explain an alt light coming on but the alt not completely failing.

What's you alt light doing during this? Have you put a meter on the battery to see what the charge is while the engine is off and running and during your symptoms?

The scrapping noise is disturbing. Is it sort of a metallic hollow sound? Like a fan blade scrapping against the fan housing? (and stopping?!? :O )

[maclaren65]

Originally Posted by flat6pilot

Generally speaking, electrical components either work or they don't (electronics are digital in nature, either on or off).

However, in the case of an alternator there is at least one analog variable: brushes. The brushes will wear overtime and COULD cause the output to get worse until it finally "dies". This is just one of many failure scenarios and could explain an alt light coming on but the alt not completely failing.

What's you alt light doing during this? Have you put a meter on the battery to see what the charge is while the engine is off and running and during your symptoms?

The scrapping noise is disturbing. Is it sort of a metallic hollow sound? Like a fan blade scrapping against the fan housing? (and stopping?!? :O )

The Alt Light didn't come on, but the headlights didn't either. The gauge lights seem really low to me too.

My mechanic said: "The first failure mode is overcharging. Then they stop charging. You only get a warning light when you turn the key on when the car is not running. The light will usually not come on when the alternator fails."

I was also thinking maybe the fan blade. I'm taking to my shop tomorrow to have it checked out. I will report back what we find.

I just got the car yesterday and was hoping to drive it around all weekend, but now I am a little cautious about venturing too far from home.

[flat6pilot]

Don't sweat it. I'm sure you have a great car. It's the accessory items that can't keep up with them. Alt, Starter, etc.....

Mine (alt) is getting "weak" too. I only have 167k on the clock too! Stretching for the winter....almost there.....

Ohh, be SURE to get a spare DME relay (under the drivers seat) while your checking things out.... LEAVE THE SPARE IN THE GLOVEBOX.

[86 911 Targa]

Richard,

Here's an idea.

Since it does not appear that you will be doing the work, take your car to someone who can perform a COMPLETE diagnostic on your electrical system.

Including an alternator load test, battery specific gravity ect...

Did you have someone perform a thorough pre-purchase inspection?

Good luck,

Gerry

[maclaren65]

Gerry: I wasn't able to have full PPI done by the Porsche shop I will use, so I used an independent German Import shop that mostly works on Mercedes and BMW and the occasional 911.

I did get a compression check and all cylinders were at 170 and the spark plugs were clean. I did do a visual inspection of the car with a mechanic, and it looked good, including inspecting the car from below.

I hope to do some of the more basic maintenance myself.

[86 911 Targa]

Originally Posted by maclaren65

Gerry: I wasn't able to have full PPI done by the Porsche shop I will use, so I used an independent German Import shop that mostly works on Mercedes and BMW and the occasional 911.

I did get a compression check and all cylinders were at 170 and the spark plugs were clean. I did do a visual inspection of the car with a mechanic, and it looked good, including inspecting the car from below.

I hope to do some of the more basic maintenance myself.

If your alternator does need replacement, the Bentley covers that repair.

It's about a two hour job for a "first timer".

I've done it twice on our '86.

There are however, a few details.

Having the alternator rebuilt "when in hand" will save you a couple hours of labor charges.

pm me with your email address.

Good luck,

Gerry

[Formerly Steve Wilkinson]

If you do pull the alternator, be sure to disconnect the battery first. It's very easy to inadvertently touch the alternator power wire to the engine block inside that confined space under the...jeez, I've forgotten what it's called, the fiberglass air shroud. (The mind is the second thing to go.)

[dtw]

Not sure what an alternator has to do with headlights failing to turn on. If there's juice (you said you were able to start the car, so there is), then the lights will come on if the switch is working. Are you sure they didn't come on? Perhaps they were on, but very dim?

An alternator load test is a relatively simple procedure. You can do it at your local FLAPS for free, generally, if you don't have the right equipment. First thing, though, would be to check the voltage across the battery at varying RPMs and load levels. That's easier and usually, as mentioned above, bad voltage regulation is the first sign of an alternator going tits-up.

Barring alternator issues, you may have a headlight switch on the way out.

[rick-l]

Originally Posted by dtw

Not sure what an alternator has to do with headlights failing to turn on.

Barring alternator issues, you may have a headlight switch on the way out.

+1 There is no indication the alternator is bad.

Did you look for marks on the fan shroud?

Next time it makes noise get out and see where it is coming from.

Headlights did not work, not just dim??? Do you have a turbo or turbo look?

[maclaren65]

I took my newly acquired 87 Carrera (Rick: it's not a Turbo or Turbo-look) to a good shop today as a drop in. The shop owner (super knowledgeable Porsche pro) gave it a very quick inspection and he wasn't sure what caused the noise yet, and wants me to schedule a full inspection next week.

The headlights have been functioning fine (dash gauge lights are still a bit dim) and the charging system seems solid so far. The fan belt is not a factory Porsche part, so maybe it was acting up the night I heard the noise. We're going to replace that this month. If I hear the noise again I'll capture it with the video function on my iPhone. So far so good.

The battery is working fine, but it looks a bit old and tired, so I decided to start fresh and I bought a new battery today. I'll install after I clean up the battery tray area (the metal has a little corrosion and needs to be neutralized and resealed).

Here's the car:
http://www.me.com/gallery/#100004