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Pelican Technical Article:

Alternator Replacement

Steve Vernon

Time:

3 hours3 hrs

Tab:

$200 to $800

Talent:

***

Tools:

13mm, 10mm, 8mm wrench, 5mm Allen

Applicable Models:

Porsche 993 Carrera (1995-98)
Porsche 993 Carrera 4 (1995-98)
Porsche 993 Carrera 4S (1996-98)
Porsche 993 Carrera S (1998)
Porsche 993 Targa (1996-98)
Porsche 993 Turbo (1996-97)

Parts Required:

Alternator

Hot Tip:

Check your wiring harness

Performance Gain:

Electrical power to the vehicle

Complementary Modification:

Change the belts

One of the nice things about the configuration of the flat six engine in the 993s is the relative ease with which you can replace the alternator. The replacement and repair process is straightforward, and should take you about an afternoon to complete.

The first thing that you need to do is to make sure that your alternator is indeed the cause of the problems with your charging system. Sometimes bizarre electrical problems can be caused by a number of faults other than the alternator. It's important to troubleshoot the system prior to replacing your alternator.

The first thing to check is the belt that drives the alternator. Is it tight and amply turning the alternator pulley? If it's worn or close to breaking, then replace it and recheck the alternator; please see our article on replacing your alternator belt for additional assistance. Modern belts seldom break, but they get brittle and glazed with age, and can slip on their pulleys.

The next item to check is the voltage at the battery. This should read a little more than 12 volts with the engine off. When the car is running, the voltage should read at in the range of 13 to 14.5 volts with the engine at 2000 rpm. If your battery appears to be leaking, then your alternator's voltage regulator has probably failed. The battery will usually only leak acid if it has been overcharged at a much higher voltage. If the voltage measured at the battery is more than 16 or 17 volts when the engine is running, then the regulator is probably bad. If your battery has boiled over and has acid overflowing out the top, make sure that you clean up any spilled acid immediately. Dousing the area with a water and baking soda solution should help considerably to neutralize the acid, and prevent it from eating away at the metal.

An important item to check on your car is the engine ground strap. The engine is electrically isolated from the chassis by rubber motor mounts. If the engine ground strap is missing or disconnected, then you might have a whole bunch of problems, including electrical system malfunctions and difficultly turning over the starter.

When working with the alternator it is a really good idea to disconnect both the positive (yellow arrow) and negative (red arrow) cables from the battery.
Figure 1

When working with the alternator it is a really good idea to disconnect both the positive (yellow arrow) and negative (red arrow) cables from the battery. At the very least remove the ground or negative cable and place it so that it cannot accidentally come in contact with the battery post while you are working. I personally remove both cables to be safe.

Like all air-cooled 911s that came before it, the 993s alternator is located behind the cooling fan and powered by a belt that connects the alternator pulley to the crankshaft pulley.
Figure 2

Like all air-cooled 911s that came before it, the 993s alternator is located behind the cooling fan and powered by a belt that connects the alternator pulley to the crankshaft pulley.

You will need to remove the A/C belt and this will include loosening the lines.
Figure 3

You will need to remove the A/C belt and this will include loosening the lines. Please see our articles on replacing your Varioram and non-Varioram A/C belt.

Next remove the belts for both the alternator and cooling fan; please see our articles on these procedures for additional instruction.
Figure 4

Next remove the belts for both the alternator and cooling fan; please see our articles on these procedures for additional instruction.

Remove the electrical panel plastic protector by lifting it up from the bottom and removing it from the right ear corner of the engine compartment.
Figure 5

Remove the electrical panel plastic protector by lifting it up from the bottom and removing it from the right ear corner of the engine compartment.

Reach in a separate the single electrical connection for the A/C compressor (red arrow) from behind the panel.
Figure 6

Reach in a separate the single electrical connection for the A/C compressor (red arrow) from behind the panel.

Place a bunch of shop towels down on the rear of the left side of the engine compartment deck and carefully move the compressor and lines out of the way.
Figure 7

Place a bunch of shop towels down on the rear of the left side of the engine compartment deck and carefully move the compressor and lines out of the way.

Use a 10mm wrench and remove the three bolts that hold the air diverter to the shroud and lift the diverter out (red arrow).
Figure 8

Use a 10mm wrench and remove the three bolts that hold the air diverter to the shroud and lift the diverter out (red arrow).

Use a 5mm Allen and remove the bolt that holds the fan housing to the motor (red arrow).
Figure 9

Use a 5mm Allen and remove the bolt that holds the fan housing to the motor (red arrow).

You can now move the fan and alternator around so that you can get at the four 10mm nuts holding the plastic cup on the rear of the alternator (red arrow).
Figure 10

You can now move the fan and alternator around so that you can get at the four 10mm nuts holding the plastic cup on the rear of the alternator (red arrow).

Tilt the alternator forward and remove the 13mm nut (red arrow) and the two 8mm nuts (yellow arrows).
Figure 11

Tilt the alternator forward and remove the 13mm nut (red arrow) and the two 8mm nuts (yellow arrows). This will free up the wiring and allow you to fully remove the fan, housing and alternator.

Porsche had a factory recall on the wiring harnesses in the 993's.
Figure 12

Porsche had a factory recall on the wiring harnesses in the 993's. You should call your dealership and see if your harness has been replaced under warranty and if not get it done, there is no cost for this. If your harness looks like this it needs to be replaced as it is a major problem for both the potential to cause a fire and/or fry your electrical system. Do not install a new alternator with a wiring harness that is in this type of shape. The coverings on the wires should be complete, soft and pliable; if yours is cracked or allowing the raw wires to contact each other replace the harness.

Separate the fan from the housing; this should come apart easily with hand pressure.
Figure 13

Separate the fan from the housing; this should come apart easily with hand pressure. Both these parts are fragile and expensive; don't just start hitting things with hammers!

Once you have the fan out of the housing you will need to separate the fan from the alternator.
Figure 14

Once you have the fan out of the housing you will need to separate the fan from the alternator. The alternator shaft sits in the fan bearing and this is a pressure fitting. You will need to use the proper puller and it helps to have three 120mm 6mm X 1mm bolts and thick washers handy.

If the fan bearing has gone bad or is starting to squeal or wobble now is a really good time to replace it.
Figure 15

If the fan bearing has gone bad or is starting to squeal or wobble now is a really good time to replace it. Press out the old one and press in a new one. Be warned that the fan is very fragile and can be easily damaged; please see our article on alternator cooling fan bearing replacement.

You can now replace the alternator.
Figure 16

You can now replace the alternator. Installation is the reverse of removal.

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