824003A 8 Mercury ECU, Engine Control Unit

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 Electronic Control Module (ECM). The sensor is powered by the sensor supply (12 VDC) from the 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, the ECM is able to calculate the positions of the pistons in the cylinders. The 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. The ECM sends voltage pulses to the ignition transformers for firing the spark plugs according to the desired timing.During engine operation, the ECM will shut down the engine if the ECM detects a problem with the signal from the speed/timing sensor. The ECM 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 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 the 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 g01325649
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 ECM P1 connector
(P1-33) Signal
(P1-43) 12 volt supply
(P1-51) Return
Perform a 45 N (10 lb) pull test on the wires that are associated with the circuit for the speed/timing sensor.
Illustration 4 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 the 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