GM Full Size Vans 1987-1997 Repair Guide

Alternator

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TESTING



See Figure 1

If you suspect a defect in your charging system, first perform these general checks before going on to more specific tests.

  1. Check the condition of the alternator belt and tighten it if necessary.
  2.  
  3. Clean the battery cable connections at the battery. Make sure the connections between the battery cables and battery clamps are good. Reconnect the negative terminal only and proceed to the next step.
  4.  
  5. With the key OFF , insert a test light between the positive terminal on the battery and the disconnected positive battery terminal clamp. If the test light comes on, there is a short in the electrical system of the van. The short must be repaired before proceeding. If the light does not come on, proceed to the next step.
  6.  

If the van is equipped with an electric clock, the clock must be disconnected.

  1. Check the charging system wiring for any obvious breaks or shorts.
  2.  
  3. Check the battery to make sure it is fully charged and in good condition.
  4.  

There are many possible ways in which the charging system can malfunction. Often the source of a problem is difficult to diagnose, requiring special equipment and a good deal of experience. This is usually not the case, however, where the charging system fails completely and causes the dashboard warning light to come on or the battery to "die". To troubleshoot a complete system failure, only two pieces of equipment are needed: a test light, to determine that current is reaching a certain point; and a current indicator (ammeter), to determine the direction of the current flow and its measurement in amps.

This test works under three assumptions:



The battery is known to be good and fully charged.
 
The alternator belt is in good condition and adjusted to the proper tension.
 
All connections in the system are clean and tight.
 

In order for the current indicator to give a valid reading, the van must be equipped with battery cables which are of the same gauge size and quality as original equipment battery cables.

  1. With the ignition switch ON and the engine not running, the charge indicator light should be on. If not, disengage the wiring harness at the alternator and use a fused jumper wire with a 5-amp fuse to ground the "L" terminal in the wiring harness.
    1. If the lamp lights, replace the alternator.
    2.  
    3. If the lamp does not light, check for an open circuit between the grounding lead and the ignition switch.
    4.  

  2.  
  3. With the ignition switch ON and the engine running, the lamp should be off. If not, stop the engine, turn the ignition switch ON , and disconnect the wiring harness.
    1. If the lamp goes out, replace the alternator.
    2.  
    3. If the lamp stays on, check for a grounded "L" terminal wire.

      Click image to see an enlarged view

      Fig. Fig. 1: Connections for the alternator output test

    4.  

  4.  
  5. If the vehicle voltmeter shows high or low voltage readings with the engine running:
    1. Disengage the wiring harness from the alternator.
    2.  
    3. With the engine off and ignition ON , connect a digital multimeter set on the DC scale, from ground to the "L" terminal in the wiring harness. The reading should equal the battery-s voltage; if not, there is an open, grounded or high resistance circuit between the terminal and the battery. Repair this circuit before performing any more tests.
    4.  

  6.  
  7. Engage the harness connector to the alternator and run the engine at 2500 rpm with the accessories off.
  8.  
  9. Measure the voltage at the battery. If it is above 16 volts, replace the alternator.
  10.  
  11. With the engine off, connect an ammeter at the alternator output terminal. The ammeter must have the capability to measure 115 amps of current.
  12.  
  13. Connect a digital multimeter set on the DC scale across the alternator and a carbon pile across the battery.
    1. Run the engine at 2500 RPM, turn on all the accessories and load the battery with a carbon pile to obtain maximum amperage. Maintain voltage at 13 volts or more.
    2.  
    3. If the output is within 15 amps of the rated output, the alternator is OK. Refer to the alternator specifications in this section.
    4.  
    5. If the output is not within 15 amps, the alternator must be replaced.
    6.  

  14.  

REMOVAL & INSTALLATION



1987-95 Models

See Figures 2, 3 and 4



Click image to see an enlarged view

Fig. Fig. 2: Before removing the positive lead from the alternator, disconnect the negative battery cable:



Click image to see an enlarged view

Fig. Fig. 3: Be careful when removing the locknut, as the terminal stud sometimes will rotate with the nut:



Click image to see an enlarged view

Fig. Fig. 4: Remove the drive belt, loosen the mounting bolts and remove the alternator:

  1. Open the hood and disconnect the negative battery cable.
  2.  
  3. On G-van models remove the engine cover and disconnect the air intake hose and resonator.
  4.  
  5. Remove the air cleaner intake duct.
  6.  
  7. Drain the coolant to a level below the upper radiator hose. Loosen the upper radiator hose clamp and disconnect the hose from the radiator and move it to one side.
  8.  
  9. Loosen the radiator fan shroud bolts.
  10.  
  11. If necessary, remove the windshield washer fluid reservoir.
  12.  
  13. If necessary, remove the hood latch cable.
  14.  
  15. If necessary, remove the radiator hold-down brackets.
  16.  
  17. Remove the fan shroud.
  18.  
  19. Disconnect and tag all wiring to the alternator.
  20.  
  21. Remove the alternator brace bolt and upper mounting pivot bolt.
  22.  
  23. Remove the drive belt.
  24.  
  25. Support the alternator and remove the lower mounting bolt. Remove the alternator.
  26.  

To install:
  1. Install the unit and tighten the lower mounting bolt to the following figures:

    All gasoline engines:18 ft. lbs. (25 Nm)
     
    All diesel engines: 32 ft. lbs. (43 Nm)
     

  2.  

  1. Install the upper mounting/pivot bolt and the drive belt.
  2.  
  3. Reconnect the wires at the alternator.
  4.  
  5. Adjust the belt to have 1 / 2 in. (13mm) depression under thumb pressure on its longest run.
  6.  
  7. Tighten the upper mounting bolt to the following figures:

    4.3L engine: 37 ft. lbs. (50 Nm)
     
    5.0L engine: 37 ft. lbs. (50 Nm)
     
    5.7L engine: 37 ft. lbs. (50 Nm)
     
    7.4L engine:18 ft. lbs. (25 Nm)
     
    Diesel engines: 20 ft. lbs. (27 Nm)
     

  8.  

  1. Place the fan shroud back in its original position.
  2.  
  3. If removed, install the radiator hold-down brackets and the hood latch cable.
  4.  
  5. If removed install the windshield washer fluid reservoir.
  6.  
  7. Install the upper radiator hose, tighten the hose clamp and replenish the cooling system
  8.  
  9. Tighten the fan shroud bolts.
  10.  
  11. Install the air cleaner intake duct.
  12.  
  13. On G-van models install the air intake hose, resonator and engine cover.
  14.  
  15. Reconnect the negative battery cable.
  16.  
  17. Close the hood, start the vehicle and check for normal operation.
  18.  

1996-97 Models
  1. Open the hood and disconnect the negative battery cable.
  2.  
  3. Remove the plastic coolant reservoir from the engine compartment.
  4.  
  5. Remove the air cleaner assembly from the engine compartment.
  6.  
  7. Remove the upper fan shroud.
  8.  
  9. Loosen the serpentine belt tensioner and slip the belt off the alternator.
  10.  
  11. Disconnect the heater hose pipe from the alternator (gasoline engines only).
  12.  
  13. Disconnect the oil fill bracket from the generator bracket (gasoline engines only).
  14.  
  15. Disconnect and tag all wiring to the alternator.
  16.  
  17. Remove the alternator front mounting bolt.
  18.  
  19. Support the alternator and remove the rear mounting bolt. Remove the alternator.
  20.  

To install:
  1. Install the unit and tighten the rear mounting bolt to 18 ft. lbs. (25 Nm)
  2.  
  3. Install the front mounting bolt and tighten it to 37 ft. lbs. (50 Nm).
  4.  
  5. Reconnect the wires at the alternator.
  6.  
  7. Loosen the serpentine belt tensioner and reinstall the belt on the alternator pulley. Release the belt tensioner.
  8.  
  9. Connect the oil fill bracket to the alternator bracket (gasoline engines only).
  10.  
  11. Connect the heater hose pipe to the alternator (gasoline engines only).
  12.  
  13. Install the upper fan shroud.
  14.  
  15. Install the air cleaner assembly.
  16.  
  17. Install the plastic coolant reservoir.
  18.  
  19. Reconnect the negative battery cable.
  20.  
  21. Close the hood, start the vehicle and check for normal operation.
  22.  

 
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