3126B Marine Engines Caterpillar

Note: If the vessel is equipped with a Multi-Station Control System (MSCS), refer to Service Manual, RENR7651, "Marine Multi-Station Control System" for the proper troubleshooting procedure.

Probable Causes

• Start interlock

• Shutdown switch

• Batteries

• Battery cables

• Starting circuit

• Starting motor solenoid

• Starting motor

• Flywheel ring gear

• Transmission

• Engine accessories

• Hydraulic cylinder lock

• Internal engine problem

Recommended Actions

Start Interlock

Note: This feature is only available on engines that are equipped with a 70 pin customer connector.

The start interlock provides a means of preventing the engine from starting through a switched circuit. The start interlock may be wired through a neutral safety switch or through another similar device. If no such device is installed, a jumper wire must be installed between terminals P61-41 and P61-42. Continuity must exist between these terminals in order for the engine to crank.

Shutdown Switch (If Equipped)

The shutdown switch is mounted on the engine. Verify that the switch is in the Run (out) position. If the switch is depressed, fuel injection is disabled and the engine will not crank.

Batteries and/or Battery Cables

1. Inspect the main power switch, bus bars, battery posts, and battery cables for loose connections and corrosion. If the battery cables are corroded, remove the battery cables and clean the battery cables. Tighten any loose connections.

2. Inspect the batteries.

   1. Charge the batteries. Refer to Special Instruction, SEHS7633, "Battery Test Procedure".

   2. Load test the batteries. Refer to Special Instruction, SEHS9249, "Use of 4C-4911 Battery Load Tester for 6, 8 and 12 Volt Lead Acid Batteries".

Starting Motor Solenoid or Starting Circuit

1. Test the operation of the starting motor solenoid. Check the condition of the engine wiring for the starting motor solenoid. Test the operation of the starting motor. For additional information, refer to Systems Operation/Testing and Adjusting.

Starting Motor or Flywheel Ring Gear

1. Test the operation of the starting motor solenoid. Check the condition of the engine wiring for the starting motor solenoid. Test the operation of the starting motor. For additional information, refer to Systems Operation/Testing and Adjusting.

2. Inspect the starting motor pinion and the flywheel ring gear for damage.

Transmission or Engine Accessories

1. Ensure free movement of the driveline.

2. Ensure that the timing pin was not left in the flywheel housing.

3. Remove any engine accessories that may lock up the engine and inspect any engine accessories that may lock up the engine.

   The following list illustrates examples of engine accessories that may lock up the engine:

   • Hydraulic pump that is driven from the rear gear group

   • Air compressor

   • Power steering pump

   • Engine oil pump

Hydraulic Cylinder Lock

Check for fluid in the cylinders (hydraulic cylinder lock) by removing the individual unit injectors.

Note: Drain the fuel from the cylinder head. Fuel will flow from the cylinder head into the cylinders when the unit injector is removed.

Internal Engine Problem

1. Disassemble the engine. Refer to Disassembly and Assembly.

2. Inspect the internal components for the following conditions:
   • Seizure

   • Broken components

   • Bent components