42768 Mercruiser NUT

Table 1
Diagnostic Codes Table    
Code and Description     Conditions which Generate this Code     System Response    
190-8 Engine Speed Sensor : Abnormal Frequency, Pulse Width, or Period     The signal from the primary engine speed/timing sensor is intermittent or the signal has been lost.     The code is logged. If a valid signal is not received from the primary engine speed/timing sensor, the Electronic Control Module (ECM) will default to the secondary engine speed/timing sensor. The engine will shut down only if the signals from the primary engine speed/timing sensor and the secondary engine speed/timing sensor are abnormal.    
342-8 Secondary Engine Speed Sensor : Abnormal Frequency, Pulse Width, or Period     The signal from the secondary engine speed/timing sensor is intermittent or the signal has been lost.     The code is logged. If a valid signal is not received from the secondary engine speed/timing sensor, the ECM will default to the primary engine speed/timing sensor. The engine will shut down only if the signals from the primary engine speed/timing sensor and the secondary engine speed/timing sensor are abnormal.    The engine uses two engine speed/timing sensors. The secondary engine speed/timing sensor monitors the camshaft gear and the primary engine speed/timing sensor monitors the crankshaft gear. Both of the engine speed/timing sensors detect the reference for engine speed and timing from a unique pattern on the respective gear. The ECM counts the time between pulses that is created by the sensor as the gear rotates in order to determine rpm.Under normal operation, the secondary engine speed/timing sensor is used to determine timing for starting purposes. The secondary engine speed/timing sensor is used to determine when the piston in the No. 1 cylinder is at the top of the compression stroke. When the timing has been established, the primary engine speed/timing sensor is then used to determine engine speed and the signal from the secondary camshaft sensor is ignored.After locating the No. 1 cylinder, the ECM triggers each injector in the correct firing order and at the correct unit injector timing. The actual timing and duration of each injection is based on engine rpm and load. If the engine is running and the signal from the primary engine speed/timing sensor is lost, a slight change in engine performance will be noticed when the ECM performs the changeover to the secondary engine speed/timing sensor. Loss of the signal from the secondary engine speed/timing sensor during engine operation will not result in any noticeable change in engine performance. However, if the signal from the secondary engine speed/timing sensor is not present during start-up the following conditions may exist:
The engine may require a slightly longer period of time to start-up.
The engine may run rough for a few seconds until the ECM determines the proper firing order by using the primary engine speed/timing sensor only.The engine will start and the engine will run when only one sensor signal is present from either of the sensors. The loss of the signal from both of the sensors during engine operation will result in the termination of injection and the shutting down of the engine by the ECM. The loss of the signal from both of the sensors during start-up will prevent the engine from starting.Both sensors are magnetic sensors with an integral connector. The two sensors are not interchangeable. Do not switch the positions of the sensor. If the sensors are replaced, a timing calibration is not necessary for the engine.Note: When the sensors are being installed, complete all of the following tasks:
Lubricate the O-ring with oil.
Ensure that the sensor is fully seated into the engine before tightening the bracket bolt.
Ensure that the connector is properly latched.
Ensure that the harness is properly secured, and ensure that the tie-wraps are placed in the correct location.
Illustration 1 g01560426
Schematic for the speed/timing sensorsTest Step 1. Check for Active Diagnostic Codes
Remove the electrical power from the ECM.
Connect Caterpillar Electronic Technician (ET) to the service tool connector.
Restore the electrical power to the ECM.
Start the engine and run the engine. The problem may occur when the engine is at any operating temperature. However, the problem is more likely to occur when the engine is at the normal operating temperature.
If the engine will not start, monitor the engine speed on Cat ET while the engine is being cranked. Cat ET may need to be powered from another battery while the engine is being cranked. This is done so that Cat ET will not reset.Note: Upon initial cranking, the status for engine speed may indicate that the engine speed signal is abnormal. This message should be replaced with an engine speed once the ECM is able to calculate a speed from the signal.
Check for one of the following logged diagnostic codes or active diagnostic codes:
190-8
342-8Expected Result:One of the above codes are active or logged.Results:
No engine rpm - Engine rpm is not indicated on Cat ET. Proceed to Test Step 2.
Active or logged code - There is an active diagnostic code or a logged diagnostic code for an engine speed/timing sensor. Proceed to Test Step 4.
No codes - Neither code is active or logged.Repair: Refer to the appropriate symptoms in Troubleshooting, "Troubleshooting Without a Diagnostic Code".STOPTest Step 2. Check the Installation of the Sensor Assembly
Remove the electrical power from the ECM.
Illustration 2 g01194044
Sensor installation (mounting detail) (1) Mounting surface (2) Flange (3) Bracket
Visually inspect the sensors without removing the sensor assembly from the engine. Flange (2) must be flush against mounting surface (1) in order to ensure proper operation.Inspect bracket (3). Verify that the bracket securely holds the flange of the sensor flush against the mounting surface.Verify that the bracket is not bent. If the bracket is bent or if an obstruction is preventing the sensor assembly from being installed correctly, the engine will not start.Note: The bracket cannot be replaced separately.
Illustration 3 g01142103
Engine speed/timing sensors (exploded view) (4) Bracket (5) Secondary speed/timing sensor (6) Mounting plate (7) O-ring seals (8) Bracket (9) Primary speed/timing sensor
Remove the suspect engine speed/timing sensor from the