DIESEL EGR/EPR SYSTEM FUNCTION SERVICE INFORMATION

EXHAUST GAS IS RECYCLED THROUGH THE COMBUSTION CYCLE BY ADMITTING EXHAUST GASES INTO THE INTAKE MANIFOLD. EXHAUST GASES ARE ROUTED FROM BOTH CYLINDER HEADS THROUGH INTERNAL PASSAGES IN THE MANIFOLD TO THE EGR VALVE (FIGURE 28). EXHAUST GAS FLOW IS A FUNCTION OF THE PRESSURE DIFFERENTIAL BETWEEN THE EXHAUST SYSTEM AND THE INTAKE MANIFOLD. THE EGR VALVE CONTROLS THE EXHAUST FLOW AT THE POINT OF DISCHARGE INTO THE INTAKE MANIFOLD. REFER TO FIGURE 29. THE EGR VALVE IS OPERATED BY VACUUM FURNISHED FROM A MECHANICALLY DRIVEN VACUUM PUMP (VIEW A). THE VACUUM SOURCE SIGNAL IS ROUTED THROUGH AN ELECTRICALLY OPERATED OPEN/CLOSE SOLENOID (VIEW A) TO THE EGR VALVE. EGR IS ADMITTED INTO THE INTAKE MANIFOLD AT IDLE, AND LIGHT LOAD FUELING RATES. THE EGR VALVE REMAINS FULLY OPEN THROUGH A CALIBRATED THROTTLE LEVER MOTION. THROTTLE POSITION IS SENSED BY AN ELECTRICAL SWITCH MOUNTED DIRECTLY TO THE R.H. SIDE OF THE INJECTION PUMP (VIEW C). AS THE THROTTLE IS OPENED, THE THROTTLE POSITION SWITCH (TPS) ELECTRICALLY CLOSES AT THE CALIBRATION POINT, ENERGIZES THE SOLENOID, AND SHUTS OFF THE VACUUM SIGNAL, ALLOWING THE EGR VALVE TO CLOSE. TO INCREASE FLOW EGR RATES, AN EXHAUST PRESSURE REGULATOR (EPR) VALVE (VIEW B) IS USED AT THE LEFT HAND EXHAUST MANIFOLD TO INCREASE EXHAUST BACKPRESSURE. AT CLOSED THROTTLE THE EPR VALVE IS CLOSED. WITH INCREASING THROTTLE POSITION THE THROTTLE POSITION SWITCH ELECTRICALLY OPENS CAUSING THE EPR VALVE TO OPEN BY SHUTTING OFF VACUUM TO THE VALVE. THE EPR VALVE IS CONTROLLED BY ITS OWN SWITCH POINT WITHIN THE THROTTLE POSITION SWITCH ASSEMBLY AND ITS OWN OPEN/CLOSE SOLENOID (VIEW A). WITH AUTOMATIC TRANSMISSION VEHICLES, THE THROTTLE POSITION SWITCH HAS AN ADDITIONAL FUNCTION OF CONNECTING AND DISCONNECTING THE TRANSMISSION CONVERTER WHEN THE THROTTLE IS OPERATED TO A CALIBRATED POINT. WHEN DEACTIVATED, THE EGR VALVE IS NORMALLY CLOSED AND THE EPR VALVE IS NORMALLY OPEN. SUMMARIZING THE EGR/EPR VALVE AND SOLENOID OPERATIONS: ENGINE SPEED IDLE TO 15F THROTTLE EGR VALVE OPEN EGR SOL. NOT ENERGIZED (VACUUM TO VALVE) EPR VALVE CLOSED EPR SOL. ENERGIZED (VACUUM TO VALVE) ENGINE SPEED 15F TO 20F THROTTLE EGR VALVE OPEN EGR SOL. NOT ENERGIZED (VACUUM TO VALVE) EPR VALVE OPEN EPR SOL. NOT ENERGIZED (NO VACUUM TO VALVE) ENGINE SPEED 20F TO FULL THROTTLE EGR VALVE CLOSED EGR SOL. ENERGIZED (NO VACUUM TO VALVE) EPR VALVE OPEN EPR SOL. NOT ENERGIZED (NO VACUUM TO VALVE) HEAVY BLACK EXHAUST SMOKE UPON ACCELERATION GENERALLY INDICATES A MALFUNCTION IN THE EGR SYSTEM. EGR/EPR PROBLEM DIAGNOSIS 1.START ENGINE AND OPERATE TO OPEN THERMOSTAT TEMPERATURE. 2.REMOVE AIR CLEANER COVER TO OBSERVE OPERATION OF EGR VALVE (VIEW A). 3.WITH ENGINE AT IDLE THE EGR VALVE SHOULD BE OPEN. (OBSERVE VALVE HEAD IN UP POSITION AND NOTICEABLE EXHAUST NOISE IN INTAKE.) IF NOT, CHECK AND CORRECT ANY ELECTRICAL AND HOSE CONNECTION WHICH MAY BE LOOSE AND/OR DISCONNECTED. 4.REMOVE VACUUM HOSE FROM EGR VALVE. THE VALVE HEAD SHOULD DROP WITH A NOTICEABLE REDUCTION IN NOISE. RECONNECT HOSE. 5.AT IDLE THE HOSE TO THE EGR VALVE SHOULD HAVE APPROXIMATELY 20 INCHES OF VACUUM. IF VACUUM IS NOT PRESENT, CHECK OUTPUT OF THE VACUUM PUMP AT THE PUMP. THE PUMP SHOULD PRODUCE A MINIMUM OF 20 INCHES OF VACUUM. 6.IF VACUUM IS PRESENT AT THE EGR VALVE BUT THE VALVE DOES NOT OPEN AND CLOSE AS THE HOSE IS PUT ON AND TAKEN OFF, THE EGR VALVE IS STUCK AND SHOULD BE CHECKED AND REPLACED IF NECESSARY. 7.MANUALLY OPERATE THE THROTTLE LEVER AT THE INJECTION PUMP THROUGH APPROXIMATELY 15F TO 20F OF TRAVEL. THE EGR VALVE SHOULD CLOSE WHEN THE TPS REACHES THE CALIBRATED POINT. 8.CHECK THE PINK WIRE TO THE TPS FOR 12 VOLTS (KEY ON). IF 12 VOLTS IS NOT PRESENT, CHECK FOR ANY LOOSE CONNECTIONS, OPEN WIRE, AND A BLOWN 20 AMP GAUGE FUSE (VIEW D).

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