The starter motors used for the 5.9L diesel engine and the 8.0L gasoline engine available in this model are not interchangeable with each other, or with the starter motors used for the other available engines. The starter motor for the 5.9L diesel engine is mounted with three screws to the flywheel housing on the left side of the engine. Each of these starter motors incorporates several of the same features to create a reliable, efficient, compact, lightweight and powerful unit. The electric motors of all of these starters have four brushes contacting the motor commutator, and feature four electromagnetic field coils wound around four pole shoes. The 3.9L, 5.2L, 5.9L and 8.0L gasoline engine starter motors are rated at 1.4 kilowatts (about 1.9 horsepower) output at 12 volts, while the 5.9L diesel engine starter motor is rated at 2.7 kilowatts (about 3.6 horsepower) output at 12 volts. All of these starter motors are serviced only as a unit with their starter solenoids, and cannot be repaired. If either component is faulty or damaged, the entire starter motor and starter solenoid unit must be replaced.
These starter motors are equipped with a gear reduction (intermediate transmission) system. The gear reduction system consists of a gear that is integral to the output end of the electric motor armature shaft that is in continual engagement with a larger gear that is splined to the input end of the starter pinion gear shaft. This feature makes it possible to reduce the dimensions of the starter. At the same time, it allows higher armature rotational speed and delivers increased torque through the starter pinion gear to the starter ring gear. The starter motors for all engines are activated by an integral heavy duty starter solenoid switch mounted to the overrunning clutch housing. This electromechanical switch connects and disconnects the feed of battery voltage to the starter motor, also engaging and disengaging the starter pinion gear with the starter ring gear. All starter motors use an overrunning clutch and starter pinion gear unit to engage and drive a starter ring gear that is integral to the flywheel (manual transmission), torque converter or torque converter drive plate (automatic transmission) mounted on the rear crankshaft flange.
Diagnosis & Testing - Starter Motor
Correct starter motor operation can be confirmed by performing the following free running bench test. This test can only be performed with starter motor removed from vehicle. Refer to Starter Specifications for starter motor specifications.
(1) Remove starter motor from vehicle. Refer to Starter Motor Removal and Installation.
(2) Mount starter motor securely in a soft-jawed bench vise. The vise jaws should be clamped on mounting flange of starter motor. Never clamp on starter motor by field frame.
(3) Connect suitable volt-ampere tester and 12-volt battery to starter motor in series, and set ammeter to 100 ampere scale (250 ampere scale for diesel engine starters). See instructions provided by manufacturer of volt-ampere tester being used.
(4) Install jumper wire from solenoid terminal to solenoid battery terminal. The starter motor should operate. If starter motor fails to operate, replace faulty starter motor assembly.
(5) Adjust carbon pile load of tester to obtain free running test voltage. Refer to Specifications for the starter motor free running test voltage specifications.
(6) Note reading on ammeter and compare this reading to free running test maximum amperage draw. Refer to Specifications for starter motor free running test maximum amperage draw specifications.
(7) If ammeter reading exceeds maximum amperage draw specification, replace faulty starter motor assembly.
Diagnosis & Testing - Starter Motor Solenoid
This test can only be performed with starter motor removed from vehicle.
(1) Remove starter motor. Refer to Starter Motor Removal and Installation.
(2) Disconnect wire from solenoid field coil terminal.
(3) Check for continuity between solenoid terminal and solenoid field coil terminal with continuity tester (Fig. 7). There should be continuity. If OK, go to Step 4. If not OK, replace faulty starter motor assembly.
(4) Check for continuity between solenoid terminal and solenoid case (Fig. 8). There should be continuity. If not OK, replace faulty starter motor assembly.