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HOMESERVICE MANUALSMERCURY1991COUGAR LS, 3.8 4REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROLS - SYSTEM/COMPONENT TESTS - 3.8LTFI-IV SYSTEMCOIL TEST
1991 Mercury Cougar LS, 3.8 4

Coil Test

1991 Mercury Cougar LS, 3.8 4SECTION Coil Test
  1. Attach negative (-) VOM lead to distributor base and measure battery voltage. Turn ignition switch to RUN position. Measure voltage at coil positive (+) terminal of ignition coil and turn ignition off. Voltage should be 10.5-12 volts. If voltage is as specified, go to next step. If voltage is not as specified, repair ignition switch or wiring circuit to coil. See appropriate wiring diagram in WIRING DIAGRAMS at the end of this article.
  2. Ensure ignition is off. Disconnect coil primary connector and inspect both contacts for corrosion or damage. Service or replace as necessary. Using a DVOM, measure primary circuit resistance. If resistance is not 0.3-1.0 ohm at 70°F, replace coil and retest system.
  3. Remove secondary coil wire from coil tower and inspect contact for signs of arcing or corrosion. Using a DVOM, measure resistance between coil tower connector and coil negative (-) terminal. If resistance is not 8000-11,500 ohms, replace coil.
RENDER: 1.0x

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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.