0390466 JOHNSON FUEL MANIFOLD ASSY.

Illustration 1 g00951975
Arrangement of the detonation sensors
The master Electronic Control Module (ECM) and the slave ECM supply 8 VDC in order to power the sensors. The detonation sensors provide electrical signals to the modules that indicate mechanical engine vibrations. Each sensor outputs an electrical signal. The signal is amplified and the signal is filtered. The frequency of the signal corresponds to the mechanical frequency of the vibrations. The amplitude of the signal is proportional to the intensity of the vibrations.The master ECM monitors the detonation sensors on the left side of the engine. The slave ECM monitors the detonation sensors on the right side of the engine. Each ECM monitors the signals in order to determine the presence and the severity of the detonation. The master ECM can retard the timing of the cylinders on the left side of the engine in order to limit detonation levels. The slave ECM can retard the timing of the cylinders on the right side of the engine in order to limit detonation levels. The timing may be retarded for a single cylinder or for more than one cylinder. The timing may be retarded for all of the cylinders, if necessary. If retardation of the timing does not sufficiently limit the detonation, the master ECM will shut down the engine.An ECM can retard timing by as few as three degrees for light detonation levels. The timing can be retarded up to six degrees for severe detonation. For most applications, the minimum allowable actual timing is ten degrees BTC (five degrees BTC for propane operation). A proportional strategy is used for advancing the timing after the timing has been retarded. The rate of advance is based upon the level of detonation. The rate is faster for lighter detonation. The fastest rate of proportional timing advance is one degree per minute.Each ECM will diagnose the detonation sensors for a signal that is shorted to the −Battery side, to the +Battery side, or for an open circuit. To avoid detecting vibrations that are not related to detonation, each ECM only monitors a detonation sensor when one of the pistons that is monitored by that sensor is between top center and 40 degrees after top center on the power stroke. Therefore, the “Block Tap” method of testing the detonation sensors does not work for the G3500C/E Engine.An input from a detonation sensor that is diagnosed by an ECM as "open/shorted to +battery" may measure 0 VDC on a voltmeter. This is caused by the lack of pull up resistors in the detonation sensor's circuits inside the ECM.Each ECM also supports related event codes when the levels of detonation warrant a reaction from the ECM. If the timing has been retarded by the maximum amount and the level of detonation remains high, the master ECM will shut down the engine. Detonation protection is disabled when the engine speed is less than 250 rpm.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 most likely causes of the diagnostic code are a poor connection or a problem in a wiring harness. The next likely cause is a problem with a sensor. The least likely cause is a problem with an ECM.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 g01114170
Schematic for the detonation sensors
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 each of the following connectors:
J2/P2 connectors
J8/P8 connectors
J4/P4 connectors
Connectors for each of the detonation sensors
Check the torque of the allen head screw for the ECM connectors.
Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit for the detonation sensors.
Illustration 3 g00929792
Detonation sensors
Check the harness and wiring for abrasion and for pinch points from the detonation sensors to each ECM.
Make sure that the detonation sensors are properly installed according to the torque in Specifications, "Detonation Sensors". Expected Result:All connectors, pins, and sockets are connected properly. The connectors and the wiring do not have corrosion, abrasion, or pinch points. All of the detonation sensors are properly installed.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 FOR DIAGNOSTIC CODES FOR THE 8 VOLT DC SUPPLY
Connect Cat ET to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".
Switch the 35 amp circuit breaker ON. Set the engine control to the STOP mode.
Observe the "Active Diagnostic" screen