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EGR Function Testing Buick Roadmaster VIII

Testing & Diagnostics 2 illustrations ~891 words

PORTED EGR VALVE

  1. Turn ignition off. Disconnect EGR vacuum hose at vacuum signal tube. Connect a hand-held vacuum pump to vacuum signal tube and apply 10 in. Hg. EGR diaphragm plate should move up and remain up for at least 20 seconds.
  2. If diaphragm moves up and holds for 20 seconds, diaphragm is operating properly. If diaphragm does not hold vacuum, EGR valve is defective. Place transmission in Park or Neutral and start engine.
  3. With engine running at normal operating temperature, push up on diaphragm. Engine RPM should decrease. If RPM decreases, EGR valve is functioning properly. Connect vacuum gauge to EGR valve vacuum supply hose. Raise engine speed to 2000 RPM and ensure adequate vacuum supply to EGR valve exists.

NEGATIVE BACKPRESSURE EGR VALVE

  1. EGR negative backpressure valve may be identified by letter "N" in last position of EGR part number. With engine off, disconnect EGR valve vacuum signal hose. Connect vacuum pump to vacuum signal tube and apply 10 in. Hg.
  2. EGR diaphragm should move up and remain up for 20 seconds. If diaphragm does not stay up for 20 seconds, EGR valve is defective. Using an assistant, again apply 10 in. Hg to signal tube. Have assistant immediately try to start engine. Observe diaphragm for movement.
  3. If diaphragm moves to a seated position (valve closed) during cranking and initial starting, EGR valve is functioning properly. If diaphragm does not move, clean or replace EGR valve.

POSITIVE BACKPRESSURE EGR VALVE

  1. EGR positive backpressure valve may be identified by the letter "P" in the last position of the EGR part number. To test EGR valve, place transmission in Park or Neutral.
  2. Set parking brake and block drive wheels. Connect tachometer. With engine running at normal operating temperature, increase engine speed to 2000 RPM.
  3. Disconnect vacuum hose from EGR valve and plug hose. EGR valve diaphragm should move down and engine RPM should increase. NOTE: On some engines with ECM-controlled EGR control solenoid, EGR vacuum is locked out in Park/Neutral and EGR control solenoid must be by-passed.
  4. Reconnect vacuum hose. Diaphragm should move up and engine RPM should decrease. A slight vibration of diaphragm plate may be noticed in backpressure EGR valves.
  5. If engine RPM changes and EGR diaphragm moves, EGR valve is functioning correctly. If engine RPM does not change and diaphragm does not move, remove EGR valve and apply 10 in. Hg to EGR vacuum signal tube. EGR valve should not open.
  6. If EGR valve opens, replace EGR valve. With vacuum still applied, direct a stream of air (15 psi maximum) into valve seat. EGR valve should open completely.
  7. If air is not available, connect a section of hose over EGR valve seat. Connect a vacuum pump to signal tube. With thumb plugging intake port of EGR valve, operate vacuum pump while alternately blowing and pausing.
  8. With vacuum present at signal tube, EGR valve should open while pressure is applied and should close when no vacuum is present.

DIGITAL EGR VALVE - 1990-1992 3.1L, 3.4L & 3.8L

Note. A Tech 1 scan tester or a tester capable of cycling ECM output devices may also be used to perform EGR function test.

  1. Turn engine off. Disconnect EGR valve electrical connector. Start engine and allow engine to idle. Using a 12-volt power source and a fused jumper wire, apply voltage to terminal "D" of EGR valve. (Scheme 1) NOTE: EGR valve wire colors may vary.
  2. Using a jumper wire with one end connected to a good ground, alternately touch remaining end of jumper wire to EGR valve terminals "A", "B", and then "C". Engine RPM should change as each EGR valve terminal is contacted. If engine RPM changes, EGR valve is functioning correctly.
  3. If engine RPM does not change, check for restriction in EGR supply tube or plugged EGR valve orifice. If EGR valve is not restricted or plugged, EGR valve is defective.

Scheme 1

Scheme 1
Scheme 1

DIGITAL EGR VALVE - 1990-91 2.3L "W" BODY VIN D

  1. Turn engine off. Disconnect EGR valve electrical connector. Start engine, and allow it to idle. Using a 12-volt power source and a fused jumper wire, apply voltage to terminal "B" of EGR valve. (Scheme 2) Using a jumper wire with one end connected to a good ground, alternately touch remaining end of jumper wire to EGR valve terminal "A" and then to terminal "C".
  2. Engine RPM should change as each EGR valve terminal is contacted. If engine RPM changes, EGR valve is functioning correctly. If engine RPM does not change, check for restriction in EGR supply tube or plugged EGR valve orifice. If EGR valve is not restricted or plugged, EGR valve is defective.

Scheme 2

Scheme 2
Scheme 2

INTEGRATED ELECTRONIC EGR VALVE - 1990

  1. Turn engine off. Connect vacuum pump to EGR valve. Apply vacuum and observe EGR valve. EGR valve should not move. If valve moves, check vent filter for restriction. Replace EGR valve if necessary.
  2. Turn ignition on and repeat step 1). When applying vacuum, EGR valve should not move. If EGR valve moves, system is malfunctioning.

DIGITAL EGR VALVE - 1993-94 3.1L, 3.4L & 3.8L (VIN 1)

Start engine. Using Tech 1 scan tester or a tester capable of cycling ECM output devices, select miscellaneous tests. With engine idling, RPM should drop and engine should idle rough as each solenoid is energized. If system operates as specified, EGR valve is functioning correctly.

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