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Home >> Chevrolet >> 1994 >> Forward Control 7.4 N >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests - Gasoline >> Emission Systems & Sub-Systems >> Exhaust Gas RECIRCULATION (C-7) >> Negative Backpressure EGR Valve

Negative Backpressure EGR Valve

  1. Check vacuum source to EGR solenoid. Repair as necessary. Disconnect EGR solenoid vacuum harness. Using hand-held vacuum pump, apply vacuum to ported vacuum side of EGR solenoid. If solenoid does not hold vacuum, replace solenoid. If solenoid holds vacuum, repeat test with ignition on. If solenoid holds vacuum, go to next step. If solenoid does not hold vacuum, check for short in Gray wire between solenoid terminal "B" and PCM terminal E1. Repair as necessary. If Gray wire is okay, replace PCM.
  2. Using jumper wire, connect DLC connector terminal "C" to ground. Repeat test. If solenoid holds vacuum, go to step  4. If solenoid does not hold vacuum, go to next step.
  3. Disconnect solenoid wiring harness connector. Using test light connected to ground, probe harness connector terminal "A". If test light does not illuminate, repair open battery feed circuit. If test light illuminates, connect test light between harness connectors. If test light illuminates, replace solenoid. If test light does not illuminate, repair open or short circuit. If wiring is okay, replace PCM.
  4. Remove jumper wire. Turn ignition off. Using hand-held vacuum pump, apply vacuum to EGR side of EGR solenoid. If EGR valve moves, go to next step. If EGR valve does not move, replace vacuum line, orifice and/or EGR valve.
  5. Using hand-held vacuum pump with gauge, apply vacuum to EGR valve. Start engine. EGR valve should close and vacuum drop. If vacuum does not drop, check EGR passages. If passages are plugged, clear passages. If passages are clear, replace EGR valve. If EGR valve closes and vacuum drops, check automatic transmission P/N switch. Repair as necessary. If no problems are found, system is okay.
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