1985 Mitsubishi Montero BaseFACTORY OEM SERVICE PROCEDURE

System Testing

  1. Check hoses for correct routing and condition. Cold start engine and run at idle. Observe the secondary EGR valve for operation as engine speed is increased to 2500 RPM. There should be NO secondary EGR operation after cold start. If the secondary EGR valve operates, replace thermo valve.
  2. Warm engine until coolant reaches 131°F (55°C). Increase engine speed to 2500 RPM. Observe the secondary EGR valve. The secondary EGR valve should operate. If secondary EGR valve is inoperative, check EGR valve and thermo valve. Replace as necessary.
  3. Detach hose (Green stripe) from thermo valve. Connect vacuum pump and apply vacuum. If no vacuum is available through thermo valve, valve is okay.
  4. Disconnect hose (Green stripe) from fitting at carburetor and connect vacuum pump to hose end. Apply 9.8 in. Hg while opening sub EGR valve (pull valve open by hand).
  5. If idle speed becomes unstable, the secondary EGR valve is okay. If idling speed remains stable, valve is NOT okay. Replace EGR valve as necessary.
Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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