1983-1985 Porsche 944 Alternator: Decoding the Critical Mid-1985 Changeover

Symptoms of a Failing 1983-1985 Porsche 944 Alternator

When the alternator begins to fail, it can't provide enough electricity to run the car and charge the battery. This leads to a variety of noticeable symptoms. Often, multiple symptoms will appear at once.

Common Failure Symptoms:

• Battery Warning Light: The most obvious sign is the battery-shaped warning light illuminating on your dashboard. This light indicates that the charging system voltage is low and the battery is not being charged correctly.
• Dim or Flickering Lights: Headlights, dashboard lights, and interior lights may appear dimmer than usual or flicker, especially at idle. As the alternator fails, it can't keep up with the electrical demand.
• Slow or Malfunctioning Accessories: You might notice that power windows operate more slowly, or the iconic pop-up headlights struggle to raise and lower. The car's radio may also cut out or function poorly.
• Whining or Grinding Noises: A common sign of alternator failure is a distinct whining sound from the front of the engine that changes pitch with engine RPM. This is typically caused by worn-out bearings inside the alternator. A grinding noise can also indicate severe bearing failure.
• Weak or Dead Battery: If the alternator isn't recharging the battery, the car will run solely on battery power until it's depleted. This can lead to difficulty starting the engine or a completely dead battery, requiring frequent jump-starts.
• Burning Smell: A smell of burning rubber or hot wires can indicate an overheating alternator or a slipping drive belt. This is a serious symptom that should be addressed immediately.

Diagnosing a Faulty Alternator

Before replacing parts, you can perform a simple test with a multimeter to confirm the alternator is the problem.

1. Set your multimeter to DC volts.
2. With the engine off, touch the multimeter probes to the positive and negative terminals of your battery. A healthy, fully charged battery should read approximately 12.5 to 12.6 volts.
3. Start the engine and let it idle. Measure the voltage across the battery terminals again.
4. A healthy alternator should be putting out between 13.5 and 14.5 volts.
5. If the voltage is still in the 12-volt range and does not increase, or if it drops as you turn on accessories like headlights and the blower fan, the alternator is not charging. If the voltage is excessively high (over 15 volts), the voltage regulator has likely failed.

Buying a Used 1983-1985 (Early) 944 Alternator

Given the age of these vehicles, a quality used OEM Bosch alternator is often a reliable and cost-effective choice compared to cheaply made new aftermarket units. When inspecting a used alternator, here’s what to look for:

• Confirm the Amperage: Ensure the unit is a 90-amp model for your early 944. The part number should correspond to one of the known early OEM numbers, such as Bosch AL29X.
• Spin the Pulley: The pulley should spin smoothly and quietly by hand. Any roughness, grinding, or excessive noise indicates bad bearings.
• Inspect the Pulley: Check the 2-groove V-belt pulley for any cracks, chips, or excessive wear in the grooves.
• Check Electrical Connections: The threaded posts for the main power cable (B+) and exciter wire (D+) should be clean, straight, and free of corrosion or damage.
• Inspect the Casing: Look for any major cracks or damage to the aluminum housing. Check the plastic rear cover and cooling fan for damage, as these are important for proper function.

Replacement Overview

Replacing the alternator on an early 944 is a manageable DIY job for those with mechanical experience. It is located on the lower passenger side of the engine. Access from both the top and bottom of the car is required.

Key Replacement Steps:

1. Safety First: Disconnect the negative battery terminal.
2. Access: Safely raise the front of the vehicle on jack stands and remove the engine undertray (skid pan).
3. Airbox Removal: From the top, remove the air filter box assembly to gain access to the top of the alternator.
4. Release Belt Tension: From underneath, loosen the pivot bolts on the A/C compressor. Then, loosen the lock nuts on the turnbuckle-style tensioner to create slack in the belt, allowing it to be removed from the pulleys.
5. Unbolt Alternator: Remove the two main 17mm mounting bolts holding the alternator to its bracket.
6. Disconnect Wiring: Disconnect the main power and exciter wires from the back of the alternator. Remove the plastic cooling duct.
7. Installation: Installation is the reverse of removal. Install the new alternator, but do not fully tighten the mounting bolts yet. Reconnect the wiring.
8. Tension the Belt: Reinstall the belt and use the A/C compressor tensioner to tighten it. The belt should be very tight, with only about 2-5mm of deflection under firm thumb pressure on its longest span.
9. Final Torque: Tighten the main alternator mounting bolts to 33 ft-lbs (45 Nm). Tighten the A/C compressor pivot bolts and tensioner lock nuts.
10. Final Checks: Reinstall the airbox and undertray. Reconnect the battery and perform the voltage test again to confirm the new alternator is charging correctly.

Rebuild vs. Replace

Rebuilding the original Bosch alternator is a very common practice for these cars. Often, the failure is due to worn-out brushes in the voltage regulator or failing bearings. Both are relatively inexpensive parts. A voltage regulator with new brushes can be replaced without even removing the alternator from the car in some cases. If you have the time and inclination, rebuilding can be the most cost-effective solution and preserves the original OEM part.

Cost to Replace a 1983-1985 Porsche 944 Alternator

Known Issues, Recalls, and TSBs

There are no official NHTSA recalls or Technical Service Bulletins (TSBs) specifically related to the alternator for 1983-1985 Porsche 944 models. The most significant known issue is the mid-1985 changeover from the 90-amp to the 115-amp unit, which causes frequent confusion for buyers. Additionally, the belt tensioner rod can corrode and break, and the plastic cooling duct often becomes brittle and fails, which can lead to premature alternator failure from overheating.

Frequently Asked Questions (FAQ)