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
Ground Circuits
- Using an ohmmeter, check for continuity to ground on ECU terminals 40 and 60 on all models except Probe 2.2L. On Probe 2.2L models check ECA terminals 3A, 3B and 3C (2A, 2B and 2C with non-turbo, manual transmission). Resistance should be zero ohms. If not, repair open to ground.
- Using a DVOM, touch negative lead of voltmeter to a good ground. Touch positive lead of voltmeter to each ground terminal. With vehicle running, voltmeter should indicate less than 1 volt. If voltmeter reading is greater than 1 volt, check for open, corrosion or loose connection on ground lead.
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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