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Alternator Replacement
 
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Pelican Technical Article:

Alternator Replacement

Nick Czerula

Time:

3 hours3 hrs

Tab:

$300

Talent:

*****

Tools:

Set of sockets, 17mm open-end wrench, flathead and Phillips screwdrivers, needle nose pliers

Applicable Models:

BMW Z3 (1996-02)

Parts Required:

Alternator, drive belt, idler pulley

Hot Tip:

Work with a cool engine.

Performance Gain:

Car will charge properly

Complementary Modification:

Change serpentine belt, idler pulley.

A 12-volt battery powers the electrical system in your vehicle. The initial job of the battery is to power the starter motor, thus cranking the engine fast enough to start. The battery also supplies voltage to the ignition system, the fuel system, lights, HVAC system, windows, door locks and multitudes of other electrical consumers throughout the car. In order to maintain the battery in a state of charge, a belt-driven electrical generator, generally referred to as an alternator, is bolted to the engine block. The belt driving the alternator is powered by the engine pulley (vibration damper). As soon as the engine starts, electrical power is generated by the alternator and supplied to the battery to recharge it.

Generation of electricity creates a significant amount of heat in the inner windings of the alternator. This heat needs to be vented and dispersed in order to prevent damage to the alternator. Air-cooling of the alternator is used in nearly all car models and most BMW models.

A faulty or failing alternator can cause many problems, from a simple discharging of the battery to an engine drivability problem. There are a few signs and tests you can perform to determine if the alternator is the root cause of your problem. If you get lucky, your battery light (charging system indicator) will illuminate to warn you of a possible failure.  When the battery light (charging system indicator) is ON, this means a voltage difference has been detected between battery positive (+) constant (terminal 30) and ignition ON circuit (terminal 15), indicating a fault in the charging system.

It is common for an alternator to fail slowly. When this begins to happen, your symptoms will be present when the electrical system has the highest load, for example at night. Driving at night, you may notice the instrument panel lights dim, or the radio or headlights flicker. This is a good indication that the alternator cannot handle the excess load.  Another sign of a charging system problem is the headlights dim or radio sound goes down when lowering your window. When the alternator can no longer charge the battery, you may park your vehicle and not be able to start it. Of course this could be a faulty battery too.

Always check the voltage of your charging system under load; voltage should be within 13.2-14.5 volts dc. To load, have the engine running at idle, turn on the headlights and HVAC blower motor. Never disconnect a battery cable while the engine is running to test the alternator; you may cause damage to the alternator or other electrical components from the surge in amperage. Before performing any tests of your alternator, charge and test your battery. If the battery is faulty, your alternator tests will not be accurate.

In this article, I'll go over the steps involved with replacing the alternator on the BMW Z3 4 and 6-cylinder engines. Be sure to work with a cool engine and disconnect the battery before beginning. Z3 models can come with a few alternator amperage ratings. Be sure your replacement alternator has the same rating as the faulty unit. You can usually find the amperage rating on the alternator housing. 

To avoid marring the paint and trim, work with a plastic prying tool or wrap a screwdriver tip with masking tape before prying out the body or interior items.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches. 

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability. 

Vehicle models change and evolve, as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Working in the trunk, disconnect the battery negative cable and cover the battery terminal so the cable does not accidentally come in contact with the disconnected cable. See our tech article on battery replacing for notes on disconnecting and reconnecting the battery.

Models with 4-cylinder engine:
BMW Z3 models equipped with a 4-cylinder engine utilize 2 multi-rib engine drive belts.
Figure 1

BMW Z3 models equipped with a 4-cylinder engine utilize 2 multi-rib engine drive belts. A small outer belt drives the A/C compressor and the larger inner belt drives the alternator, coolant pump, and power steering pump. Some models have an idler pulley on the main drive belt and some do not. Use this diagram to aid with removing and installing your drive belt. When removing the belt to replace the alternator, you only have to slide it off the alternator pulley and place it aside.

Using a flathead screwdriver, loosen the secondary air pump inlet hose clamp.
Figure 2

Using a flathead screwdriver, loosen the secondary air pump inlet hose clamp. (green arrow)

Then remove the secondary air inlet hose from the air filter housing by pulling it straight off.
Figure 3

Then remove the secondary air inlet hose from the air filter housing by pulling it straight off. (green arrow) Then pull it off the air pump and store in a safe place.

Next, you will unclip the three air filter housing retaining clips.
Figure 4

Next, you will unclip the three air filter housing retaining clips. (green arrows). One of the clips was hidden beneath the secondary air inlet hose. You will have to reach in behind air filter housing to access it.

Disconnect the intake air sensor electrical connector by pressing the wire release tab and pulling the connector straight off.
Figure 5

Disconnect the intake air sensor electrical connector by pressing the wire release tab and pulling the connector straight off.

Working at the air flow meter, twist electrical connector counterclockwise to disconnect.
Figure 6

Working at the air flow meter, twist electrical connector counterclockwise to disconnect. (green arrow). Then loosen the air flow meter hose clamp (yellow arrow). Once loose, remove the air filter housing from the engine compartment.

Then, loosen the secondary throttle body hose clamp at the rear air boot (green arrow).
Figure 7

Then, loosen the secondary throttle body hose clamp at the rear air boot (green arrow).

Once loose, pull the intermediate throttle out of the boot.
Figure 8

Once loose, pull the intermediate throttle out of the boot. You can leave the cables connected, just lay it aside.

Next you have to disconnect the secondary air pipe from the pump.
Figure 9

Next you have to disconnect the secondary air pipe from the pump. Squeeze the release tabs, then pull the pipe straight off the secondary air valve to remove.

Now it is time to unbolt the secondary air pump.
Figure 10

Now it is time to unbolt the secondary air pump. You will have to lift it up to disconnect the electrical at the bottom. Start by removing the two 13mm nuts (green arrows) that secure the pump to the support bracket.

Then working at the back of the pump bracket, remove the wiring harness from the mounting clip.
Figure 11

Then working at the back of the pump bracket, remove the wiring harness from the mounting clip. (green arrow)

Lift the pump up and off the bracket.
Figure 12

Lift the pump up and off the bracket. You will have to push the pump toward the firewall to clear the plastic clip on the rear of the bracket. Then, remove the purge valve from the pump by pulling it straight up and off the mounting bracket. (green arrow) The purge valve is housed in a rubber mount, if it is stuck, lubricate it with dish soap to help get it off.

Lift the secondary air pump off the mounting bracket and disconnect electrical connector by squeezing tabs and pulling is straight off.
Figure 13

Lift the secondary air pump off the mounting bracket and disconnect electrical connector by squeezing tabs and pulling is straight off.

Next, you have to loosen two 10mm nuts about 10 turns from the lower air filter housing (green arrows).
Figure 14

Next, you have to loosen two 10mm nuts about 10 turns from the lower air filter housing (green arrows). This will be enough to get it out.

With the lower air filter housing unbolted, lift it up, fastener side first, feeding the intake tube (green arrow) out of the shroud at radiator.
Figure 15

With the lower air filter housing unbolted, lift it up, fastener side first, feeding the intake tube (green arrow) out of the shroud at radiator.

Using a small flathead screwdriver, remove the tensioner dust cap.
Figure 16

Using a small flathead screwdriver, remove the tensioner dust cap. (green arrow). Gently lever off the cap by prying at edge.

To release tension on the belt, use a16 mm socket to rotate the tensioner counterclockwise and slide belt off pulleys.
Figure 17

To release tension on the belt, use a16 mm socket to rotate the tensioner counterclockwise and slide belt off pulleys.

Remove belt from alternator, then place out of the way.
Figure 18

Remove belt from alternator, then place out of the way. You do not have to remove it. With the air pump and air filter housing removed, you now have access to the alternator.

Working at the power steering reservoir, remove the two 10mm fasteners (green arrows).
Figure 19

Working at the power steering reservoir, remove the two 10mm fasteners (green arrows). Be sure not to lose the washers when removing. Lift the power steering pump off its mounting bracket and place it aside.

Next, remove the two 16mm alternator fasteners (green arrows).
Figure 20

Next, remove the two 16mm alternator fasteners (green arrows). Once loose, slide them out of alternator and store in a safe place.

If the alternator is stuck or wonÂ't come off easily once the fasteners are removed, use a flathead screwdriver and lever between the alternator and the mounting bracket.
Figure 21

If the alternator is stuck or wonÂÂ't come off easily once the fasteners are removed, use a flathead screwdriver and lever between the alternator and the mounting bracket. Slide it off the top bracket, then lift the alternator up to access the electrical connections at the back.

Working at the back of the alternator, open the rubber cover (green arrow) to expose the electrical connections.
Figure 22

Working at the back of the alternator, open the rubber cover (green arrow) to expose the electrical connections. Then remove both electrical connection nuts (yellow arrows), one is a 10mm the other is a 13mm.

If reinstalling an old or used alternator, you may have to move the bushing (green arrow) out of mounting ear for proper fit to alternator bracket.
Figure 23

If reinstalling an old or used alternator, you may have to move the bushing (green arrow) out of mounting ear for proper fit to alternator bracket. To do this, thread bolt into bushing, then place a 24mm socket under bushing, using a small hammer tap lightly to drive bushing flush with mounting ear. Be very careful and do not use too much force, damage to alternator may occur. Attach electrical connections to back of new alternator and tighten. Install new alternator in alternator bracket. Then install fasteners and tighten. Install drive belt and check that belt is properly aligned in alternator pulley. Then reassemble remaining items in reverse order of the removing steps. Connect battery negative cable. Check operation of charging system and alignment of drive belts.

 Models with 6-cylinder engine:
BMW Z3 models with a 6-cylinder engine utilize 2 multi-rib engine drive belts driven by the crankshaft.
Figure 24

BMW Z3 models with a 6-cylinder engine utilize 2 multi-rib engine drive belts driven by the crankshaft. Automatic tensioners are used to maintain belt tension and an idler pulley is used on the accessory belt to achieve proper belt wrap. Mark direction of belt rotation before removing if reusing belt. When replacing alternator, you only have to remove alternator drive belt from alternator pulley and move aside, it does not have to be removed from the engine.

Remove the air filter housing assembly.
Figure 25

Remove the air filter housing assembly. Remove the 10mm fastener (green arrow), then disconnect air flow meter electrical connector (yellow arrow). Now loosen the air flow meter clamp (red arrow) and lift the air filter housing out of the engine compartment. Remove cooling fan shroud. See our tech article on radiator cooling fan replacing. Remove engine drive belt from alternator pulley and lay aside. See our tech article on engine drive belt replacing.

Working below alternator, disconnect cooling duct (yellow arrow).
Figure 26

Working below alternator, disconnect cooling duct (yellow arrow). Grasp the duct and pull away from alternator while rocking back and forth.

Working at the back of alternator, disconnect electrical connector (yellow arrow).
Figure 27

Working at the back of alternator, disconnect electrical connector (yellow arrow). Then remove alternator positive (+) cable fastener (17mm) (green arrow), and remove cable from alternator.

Working at top of alternator, remove idler puller dust cap.
Figure 28

Working at top of alternator, remove idler puller dust cap.

Then loosen idler pulley bolt.
Figure 29

Then loosen idler pulley bolt. Bolt size may vary, 16mm is common.

Slide bolt out of alternator and remove pulley from engine.
Figure 30

Slide bolt out of alternator and remove pulley from engine.

Working at bottom of alternator, loosen lower alternator mounting bolt (green arrow).
Figure 31

Working at bottom of alternator, loosen lower alternator mounting bolt (green arrow).

Working at bottom of alternator, remove lower alternator mounting bolt.
Figure 32

Working at bottom of alternator, remove lower alternator mounting bolt.

Next remove alternator from mounting bracket by rocking back and forth while pulling up and off bracket.
Figure 33

Next remove alternator from mounting bracket by rocking back and forth while pulling up and off bracket. Once you wiggle it out of mounting bracket, remove alternator from engine compartment. Before installing alternator, it's a good idea to check the alternator cooling duct for debris. Leaves and other road debris can get trapped in the duct, preventing proper alternator cooling. This could lead to an overheated alternator and a charging system failure.

If reinstalling an old or used alternator, you may have to move the bushing (green arrow) out of mounting ear for proper fit to alternator bracket.
Figure 34

If reinstalling an old or used alternator, you may have to move the bushing (green arrow) out of mounting ear for proper fit to alternator bracket. To do this, thread bolt into bushing, then place a 24mm socket under bushing, using a small hammer tap lightly to drive bushing flush with mounting ear. Be very careful and do not use too much force, damage to alternator may occur. Install alternator in alternator bracket. Working at bottom of alternator, install lower alternator mounting bolt.

Install idler pulley through alternator and fasten to engine.
Figure 35

Install idler pulley through alternator and fasten to engine. Check that idler puller alignment tab is properly aligned with notch in alternator. Torque bolt to 70 Nm (44 ft-lb). Tighten lower alternator fastener. Connect electrical at rear of alternator and install positive cable to alternator (M8 nut 13Nm (10 ft-lb). Install alternator cooling duct. Next reinstall drive belts. Reassemble radiator cooling fan, air filter housing, and intake air duct. Connect battery negative cable. Check operation of charging system and alignment of drive belts.

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Page last updated: Sat 12/3/2016 02:07:06 AM