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Home >> Jeep >> 1989 >> Wagoneer >> Repair and Diagnosis >> Engine Performance >> System >> EGR System >> Valve Closing Test >> 4.2L & 5.9L Only
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4.2L & 5.9L Only

  1. With engine at normal operating temperature and at idle, manually open EGR valve diaphragm. RPM should immediately drop, indicating the EGR valve is not leaking and has been properly cutting off exhaust gas flow at idle.
  2. If there is no change in RPM and engine is idling properly, exhaust gases are not reaching combustion chamber. Check for plugged passage between EGR valve and intake manifold.
  3. If engine idles poorly and RPM is not greatly affected by manually opening EGR valve diaphragm, EGR valve is not closing off exhaust gas flow to intake manifold. Check for defective vacuum hoses, improper hose connection or defective EGR valve. Repair, correct or replace as needed.
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