Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1990 Mercury Grand Marquis LSFACTORY OEM SERVICE PROCEDURE
TFI-IV Module
- Remove distributor from engine and remove TFI module from distributor. Measure resistance between TFI-IV module terminals. See TFI-IV MODULE RESISTANCE table. See Fig 1 .
- If resistance measurements agree with table, replace stator. If resistance measurements are NOT as specified, replace TFI-IV module.
TFI-IV MODULE RESISTANCE
| Measure Resistance Between Terminals | Resistance Should Be: |
|---|---|
| GND-PIP IN | Greater Than 500 |
| PIP PWR-PIP IN | Less Than 2000 |
| PIP PWR-TFI PWR | Less Than 200 |
| GND-IGN GND | Less Than 2 |
| PIP IN-PIP | Less Than 200 |
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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