Alternator & Regulator - Mitsubishi Nissan 300ZX Z31

DESCRIPTION

Mitsubishi alternators are conventional 3-phase, self-rectifying type units containing 6 diodes (3 positive and 3 negative) which are used to rectify current. A case-mounted Integrated Circuit (IC) regulator is used on all models.

ALTERNATOR APPLICATIONS

Scheme 1

1. With engine idling, measure voltage at "B+" terminal. (Scheme 1) Increase engine speed to 2000 RPM. If voltage is higher than at idle, go to step 8). If not, go to next step.
2. Shut off engine but leave ignition on. Measure voltage between terminal "L" and ground. If reading is 0-1 volts, go to next step. If reading equals battery voltage, go to step 5). If reading is 1-3 volts, go to step 8).
3. Using a jumper wire, connect "B+" and "R" terminals. Repeat step 2). If reading is still 0-1 volts, go to next step. If reading is now 1-3 volts, charging circuit wiring is defective (including ignition switch ground).
4. Turn ignition off and remove jumper wire. Disconnect alternator 2-wire connector. Check continuity between alternator "L" and "R" terminals. If reading is 35-100 ohms or if there is no continuity, IC regulator is defective.
5. With ignition on, measure voltage between terminal "F" and ground. (Scheme 1) DO NOT allow voltmeter test lead to touch alternator housing. If reading equals battery voltage, IC regulator is defective.
6. If reading is 0-.50 volts, brush-to-rotor slip ring contact is poor or rotor is defective. If reading is.50-2.0 volts, diode assembly positive diodes are shorted. Go to next step. (Scheme 1): Alternator Terminal Locations
7. Turn ignition off and disconnect alternator 2-wire connector. Measure voltage between terminal "L" and ground. If reading equals battery voltage, diode assembly positive diodes are grounded. Replace diode assembly.
8. Disconnect wire from "B+" terminal. Connect ammeter (60 amps or more) between wiring and "B+" terminal. Turn on all electrical accessories. Start engine and immediately increase speed to 2500-3000 RPM. Note maximum reading on ammeter.
9. If alternator output is less than 70% of rated output, alternator is defective. If output is 70-90% of rated output, go to next step. If output is 90% or more, alternator output is okay.
10. Carefully check wiring between alternator "B+" terminal and battery positive post for poor contact. Leave accessories on for 2-3 minutes to slightly discharge battery.
11. Start engine and immediately increase speed to 2500-3000 RPM. Note maximum reading on ammeter. If alternator output is less than 90% of rated output, alternator is defective. If output is 90% or more, alternator output is okay. Go to next step.
12. Connect ammeter and voltmeter to vehicle. Start and run engine at 2500-3000 RPM. Check ammeter and voltmeter readings. Voltmeter reading must be 13.9-14.9 volts. Ammeter reading must be less than 5 amps. If reading is more than 5 amps, charge or replace battery, then re-test.

OVERCHARGED BATTERY TEST

1. Connect voltmeter between "B+" terminal and ground. Start engine and slowly increase engine RPM. If reading is 15.5 volts or more, IC regulator is defective. If not, go to next step.
2. Measure and compare voltage at terminal "F" during idle and at 3000 RPM. If reading is higher at 3000 RPM, go to next step. If not, alternator or IC regulator is defective. Terminal "F" voltage may not increase if battery is discharged.
3. Connect ammeter and voltmeter to vehicle. Start and run engine at 2500-3000 RPM. Check ammeter and voltmeter readings. Voltmeter reading must be 13.9-14.9 volts. Ammeter reading must be less than 5 amps. If reading is more than 5 amps, charge or replace battery, then retest.

DISASSEMBLY

1. Carefully remove rotor and vane assembly from shaft to prevent damage to vanes or "O" ring. Tape shaft splines to prevent damage to oil seal.
2. Remove 3 through bolts. Insert screwdriver between front housing and stator and pry downward to separate. On some models, stator and rear cover may be hard to remove as a ring is used to lock rear bearing. NOTE: Heat center of rear cover using a 200-watt soldering iron to facilitate rear stator and cover removal.
3. Place rotor in a soft-jawed vise with pulley side up. Remove nut, washer, pulley, fan (if equipped) and spacer(s). Remove rotor drive end housing and 2 seals. Remove rotor from vise. Press rotor out of front housing. Remove bearing retainer (if equipped) and front bearing.
4. Remove brush holder screws, rectifier screws, and nut from terminal "B+". Remove stator assembly from diode end housing. Detach slinger from brush holder (if equipped). Unsolder 3 stator leads from main diodes on rectifier.
5. When separating rectifier from brush holder, unsolder 2 plates soldered to rectifier. Remove condenser from "B+" terminal. Lift out rectifier assembly and brush holder. Remove vacuum pump oil seal (if equipped).

Note. Hold stator lead with needle nose pliers to prevent rectifier from overheating.

Exploded View of Mitsubishi Alternators. Scheme 2

Diode Assembly

1. Check each diode with ohmmeter in both directions. If diodes show large resistance in one direction and small resistance in other direction, diodes are normal.
2. If diodes show small resistance in both directions, it is shorted. If large resistance is shown in both directions, diode is open. If any diodes are defective, replace rectifier assembly.

Rotor

Check continuity across rotor slip rings. A reading of 3.4 ohms must be obtained. If there is no continuity, replace rotor. Check continuity between individual slip rings and rotor core/shaft. If there is continuity, rotor coil or slip ring is grounded. Replace rotor.

Stator

Ensure no continuity exists between stator coil leads and stator core. Check continuity between leads of stator coil. If there is no continuity, replace stator.

Brushes

1. Replace brushes if worn to limit line. Standard brush spring tension should be 12-16 oz. (340-453 g). Replace if less than 7 oz. (198 g) or if springs are corroded.
2. To remove brushes from holder, unsolder pigtail from terminal. To replace, solder pigtail to terminal ensuring 1/4" of brush will be located in brush holder.

REASSEMBLY

1. To assemble, reverse disassembly procedure. Solder rectifier leads as quickly as possible to prevent damage to diodes. When installing rotor assembly in rear housing, hold brushes in position by inserting a wire into access hole of rear housing. Remove brush retaining wire after assembly.
2. On diesel engine alternators, install vacuum pump vanes with rounded edges outward. Install housing and push it toward rotor before tightening bolts. (Scheme 3) Lubricate pump before operating alternator.

Installing Vacuum Pump. Scheme 3