854811 Mercury NUT, Special (#6-32)

Illustration 1 g01089416
Speed/Timing sensor and timing ring
Use this procedure to troubleshoot suspect problems with the circuit for the speed/timing sensor.This procedure covers the following diagnostic codes:
320-3 Speed/Timing Sensor short to +batt
320-7 Speed/Timing Sensor improper response
320-8 Engine Speed/Timing signal abnormalThe speed/timing sensor provides information about engine speed and the position of the crankshaft to the master Electronic Control Module (ECM) and the slave ECM. The sensor is powered by the sensor supply (12 VDC) from the master ECM. A magnetic pickup is located underneath the plastic sliphead of the sensor. The timing ring is mounted on the rear of the left camshaft. As the teeth of the ring rotate past the sliphead of the sensor, the sensor generates a signal that matches the pattern of the teeth.The timing ring has a special tooth pattern that indicates the position of the camshaft and the direction of rotation. The timing ring has 24 slots in the outer diameter. 21 of the slots are narrow. Three of the slots are about 2.5 times wider than the rest of the slots. When the engine rotates in the normal direction, the slots pass the speed/timing sensor in the following order:
1 wide slot
3 narrow slots
2 wide slots
18 narrow slotsThe number one cylinder is at the top center position when the rising edge of the third narrow slot passes the center of the sliphead. All 24 teeth pass the sliphead during one revolution of the camshaft or two revolutions of the crankshaft.With the information from the engine speed/timing sensor, each ECM is able to calculate the positions of the pistons in the cylinders. Each ECM determines the desired ignition timing according to the engine speed and load. If detonation is detected in any of the cylinders, the appropriate ECM retards the timing of the affected cylinders. Each ECM sends voltage pulses to the ignition transformers for firing the spark plugs according to the desired timing.During engine operation, the master ECM will shut down the engine if either ECM detects a problem with the signal from the speed/timing sensor. The ECM that detected the problem with the signal will activate the corresponding diagnostic code.If there is a problem with the engine speed/timing sensor's signal during start-up but no corresponding diagnostic code is active, the master ECM will not initiate the ignition. The engine will not start. The corresponding diagnostic code is not activated.The most likely causes of the diagnostic code are a poor electrical connection or a problem in a wiring harness. The next likely cause is a problem with the engine speed/timing sensor. The least likely cause is a problem with an ECM.Logged diagnostic codes provide a historical record. Before you begin this procedure, use Caterpillar Electronic Technician (ET) to print the logged codes to a file.The troubleshooting procedure may generate additional diagnostic codes. Keep your mind on correcting the cause of the original diagnostic code. Clear the diagnostic codes after the problem is resolved.
Illustration 2 g01302636
Schematic for the circuit of the speed/timing sensor
Test Step 1. INSPECT THE ELECTRICAL CONNECTORS AND WIRING
Remove the electrical power from the engine. Note: For the following steps, refer to Troubleshooting, "Electrical Connectors - Inspect".
Thoroughly inspect the following connections:
J1/P1 connectors
J7/P7 connectors
Check the torque of the allen head screw for the ECM connectors.
Illustration 3 g01055533
Harness side of the master ECM P1 connector
(P1-33) Signal
(P1-43) 12 volt supply
(P1-51) Return
Illustration 4 g01114284
Harness side of the slave ECM P3 connector
(P3-33) Signal
Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit for the speed/timing sensor.
Illustration 5 g01525136
Left side view
(1) Speed/timing sensor
Check the harness and wiring for abrasion and for pinch points from the speed/timing sensor to each ECM. Expected Result:The connectors, pins, and sockets are connected properly. The connectors and the wiring do not have corrosion, abrasion, or pinch points.Results:
OK - The components are in good condition with proper connections. Proceed to Test Step 2.
Not OK - The components are not in good condition and/or at least one connection is improper.Repair: Perform the necessary repairs and/or replace parts, if necessary.STOPTest Step 2. CHECK THE SENSOR
Set the engine control to the OFF/RESET mode. Switch the 35 amp circuit breaker OFF.
Remove the speed/timing sensor.
Illustration 6 g00931748
Plastic sliphead for the speed/timing sensor
Inspect the condition of the plastic sliphead. Look for signs of wear and for contaminants. Clean any debris from the plastic sliphead.
Check the tension of the plastic sliphead. Gently extend the plastic sliphead for a minimum of 4 mm (0.16 inch). Then push back the plastic sliphead. Expected Result:The sensor is in good condition. At least 22 N (5 lb) of force is required to push in the plastic sliphead from the extended position.Results:
OK - The sensor is not damaged. The tension of the plastic sliphead is correct.Repair: Install the sensor.
The plastic sliphead must be fully extended when the speed/timing sensor is installed so that the sensor maintains the correct clearance with the timing ring. If the correct clearance is not maintained, the signal from the sensor will not be generated.Do not install the sensor's plastic sliphead between the teeth of the timing ring. Damage to the plasic sliphead will result. Before installing the sensor, ensure that a tooth of the ring is visible in the mounting hole for the sensor.
Use the following steps to install the speed/timing sensor:
Ensure that a tooth on the timing ring is visible in the mounting hole for the sensor.
Fully extend the sliphead. Note: The plastic sliphead is designed to contact the tooth of the timing ring during installation. As the timing ring begins to turn, the radial runout of the timing ring will push the plastic sliphead into th