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.
1986 Mercury Grand Marquis LS, 4D SedanFACTORY OEM SERVICE PROCEDURE
Fuel Injection System - Multi-Point: Testing: Injectors
- Connect tachometer to engine and disconnect ISC motor. Run engine at 2000 RPM and lock speed with throttle body stop screw. As engine continues to run, disconnect and reconnect each injector individually. If each injector causes drop in engine speed of at least 150 RPM, injectors are giving proper fuel delivery.
- Replace any injectors that do not cause sufficient drop in engine speed. When test is completed and all injectors cause equal drop in speed, shut off engine. Reconnect ISC motor and reset curb idle. Refer to emission control specifications on decal in engine compartment.
- Disconnect all injector harness connectors. Using digital ohmmeter, check resistance across terminals of each injector. Ohmmeter should read 2.0-2.7 ohms on 1.9L and 2.3L Turbo engines, 16.0-18.0 ohms on 3.0L engines or 15.0-19.0 ohms on 5.0L engines. If not, replace injector.
NOTE:
For further component testing, see FORD MOTOR CO. ELECTRONIC ENGINE CONTROL IV in COMPUTERIZED ENGINE CONTROL section.
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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