777594 Mercruiser FUEL PUMP ASSEMBLY

Table 1
Diagnostic Codes Table    
CDL Code and Description     Conditions which Generate this Code     System Response    
91-8 Throttle Position Sensor abnormal frequency, pulse width, or period     The Electronic Control Module (ECM) detects an incorrect frequency on the throttle signal or an incorrect duty cycle on the throttle signal.
This code is used when the parameter for the "Desired Speed Input Configuration" is configured to "PWM".     The code is logged. The ECM flags the throttle position as invalid data and a default value is used. The engine speed may be limited to high idle.    The speed control provides a throttle signal and a droop signal to the ECM. The output for rated speed is a pulse width modulated signal (PWM) at a constant frequency. The speed signal varies with the position of the speed adjust potentiometer. The output for droop is a PWM signal at a constant frequency. The droop signal varies with the position of the droop adjust potentiometer. The output signal is referred to as a duty cycle or as a PWM signal. The output signal of the speed adjust is expressed as a percentage between 0 and 100 percent. The output signal of the droop adjust is expressed as a percentage between 0 and 10 percent.The ECM calculates the desired engine rpm from the rated speed signal and the droop signal. The rated speed signal is valid when the duty cycle is in the range of 5 to 95 percent. If the ECM determines that the rated speed signal is invalid, the engine rpm will be set to the programmed low idle.The droop signal is valid when the duty cycle is in the range of 15 to 85 percent. If the ECM determines that the droop signal is invalid, the engine will run with no droop which is referred to as isochronous mode.Some applications may choose not to use the speed control. Some applications may use a load sharing module. The load sharing module is configured to provide the engine control with a rated speed signal. The signal has the same characteristics as the above defined signal. Some of these load sharing modules cannot provide a signal until the engine is running. In these cases, troubleshooting should be performed while the engine is running.
Illustration 1 g03364312
Typical schematic
Illustration 2 g03323693
Terminal locations at the P1 ECM connector (P1-5) Digital return (P1-10) Rated speed signal
Table 2
Troubleshooting Test Steps    Values    Results    
1. Inspect the Electrical Connectors and the Wiring
A. Turn the main disconnect switch to the OFF position.
B. Thoroughly inspect connectors (P1), and (P2). Inspect all of the connectors in the harness from the engine interface connector to the speed control that are associated with the circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
C. Perform a
45 N (10 lb) pull test on each of the wires in the ECM connectors, the engine interface connector, and the connector for the EMCP that are associated with the circuit.
D. Check the torque of the allen head screws for each of the ECM connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
E. Check the harness and the wiring for abrasion and for pinch points from the batteries to the ECM.
   
Connectors    
Results: The connectors and wiring appear to be OK.
Proceed to Test Step 2
Results: The connectors and/or wiring are not OK.
Repair: Repair the wiring and/or the connectors. Replace