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Home >> GMC >> 1982 >> Magnavan Automatic Trans, Trans Mfr CD 475/M40 >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 1 (EGR Function Testing - General Motors Trucks) >> EGR Function Testing - General Motors Trucks >> Test 1 >> Ported & Backpressure EGR

Ported & Backpressure EGR

WARNING: This page is about a different variant/trim than selected.
  1. Install vacuum gauge between EGR valve and carburetor vacuum port. With engine at normal operating temperature, increase engine speed to about 3000 RPM. Vacuum gauge should read at least 5 in. Hg.
  2. Check EGR Thermal Vacuum Switch (TVS) operation by installing a vacuum gauge between TVS and vacuum source and noting presence of vacuum with engine running and at normal operating temperature.
  3. Turn engine off. Manually depress/push in EGR valve diaphragm. While depressed, hold finger over source tube and release diaphragm. Check for diaphragm and seat movement. Diaphragm should take at least 20 seconds to move to seated position. If not, replace EGR valve.
  4. Start engine. Using a hand-held vacuum pump, apply vacuum to EGR valve. EGR valve should open and engine should run rough or stall. If EGR valve does not open, replace EGR valve. If EGR valve opened, but idle quality did not change, clean plugged EGR ports.
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