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.
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HOMESERVICE MANUALSMERCURY1987GRAND MARQUIS LS, 2D SEDANREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMFUEL INJECTION SYSTEM - MULTI-POINTTESTINGFUEL DELIVERY SYSTEM TEST - 1.9L
1987 Mercury Grand Marquis LS, 2D Sedan
Fuel Delivery System Test - 1.9L
1987 Mercury Grand Marquis LS, 2D SedanSECTION Fuel Delivery System Test - 1.9L
- Check fuel tank for adequate fuel supply. Check for fuel leakage at all fittings and lines. Using volt-ohmmeter (VOM), check fuel pump electrical circuit for voltage supply and continuity. Disconnect harness connector just forward of fuel pump inlet. Connect VOM to body wiring harness connector. Turn ignition on while watching VOM.
- VOM reading should rise to 10 volts or more then return to zero volts after approximately one second. If not as specified, check inertia switch and electrical system. Check fuel pump continuity. Connect VOM to pump wiring harness connector. If there is no continuity, check directly at pump terminals. If no continuity at pump terminals, replace pump. If there is continuity shown at pump terminals, service or replace wiring harness.
- Check fuel delivery volume. Disconnect return line at fuel rail, being careful to avoid spilling fuel. Connect hose from fuel rail fitting to calibrated container of at least one quart. Connect Fuel Pressure Gauge (T80L-9974-A) to fuel diagnostic valve on fuel rail.
- Remove fuel pump relay, located on left side of dashboard. Install modified fuel pump relay. Run extended ground lead from modified relay to convenient point. Activate fuel pump for 10 seconds by grounding extended ground lead from relay. Observe pressure on gauge. If there is no pressure, check voltage supply from relay through inertia switch to fuel pump. Repair as necessary.
- Check delivery volume after all fuel has drained from hose into container. Fuel pump is operating properly if fuel pressure reaches 35-45 psi (2.5-3.2 kg/cm2 ), delivery volume is minimum of 5.6 ozs. (.17L) for 10 seconds, and residual pressure holds at minimum of 30 psi (.211 kg/cm2 ) immediately after pump is shut off.
- If all 3 conditions are met, fuel pump is operating normally. Check for engine and electrical problems. If pressure is good but volume is not, check for restricted filters or supply lines. After correcting any blockage, recheck. If volume requirements are still not met, replace fuel pump.
- If both delivery pressure and volume requirements are met, but residual pressure does not hold, check for leaking regulator or injectors. If both test good, replace fuel pump/sending unit. If no flow or pressure is seen, fuel system should be checked as in step 6). If no trouble is found, replace fuel pump/sending unit.
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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.