1991 Mercury Cougar LS, 3.8 4FACTORY OEM SERVICE PROCEDURE

Electronic EGR Valve

  1. Connect vacuum gauge to valve. Start engine. Apply 6-10 in. Hg to EGR valve and hold. Engine speed should drop at least 100 RPM or stall. Vacuum should not drop more than 1 in. Hg in 30 seconds.
  2. Check vacuum lines for correct routing. Disconnect vacuum hose at EGR valve and connect vacuum gauge to hose. On 1.9L EFI, disconnect idle air by-pass valve. On all models, accelerate engine to 2000-2500 RPM and release throttle. Repeat 8-10 times and check for consistent response.
    NOTE: EGR Vent Solenoid (EGR-VSOL) allows a small vacuum signal (less than 2.5 in. Hg) at idle.
  3. If vacuum rises above zero with cold engine, EGR solenoid is leaking and should be replaced. With engine at normal operating temperature, vacuum should rise above 15 in. Hg and return to zero when throttle is released. If EGR system operates as indicated, system is functioning correctly.
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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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