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1991 Mercury Grand Marquis Problems

RepairPal has identified the most common problems with the 1991 Mercury Grand Marquis based on complaints from actual vehicle owners. We'll tell you what the problem is and what it'll take to fix it.

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7
Known Problems

A spring in the seat belt buckle may wear or fail, causing the airbag light on the instrument panel to illuminate. Failed buckles will require replacement.

The 1996-2001 Mercury Grand Marquis with a 100% plastic intake manifold  is known for engine overheating, even with normal use, and a coolant leak from the front of the manifold. This will often trigger the check engine light and low engine coolant warning light.

The engine coolant leak is from a factory defect, which causes cracking on the front coolant passage of the intake manifold. In a very short time, this leak will lead to engine overheating issues, especially while the vehicle is idling.   

Between 1999 and 2001, Ford released an updated version of this engine, known as the 'PI' version with a metal coolant passage on the front of the intake manifold, to prevent future issues.

There is no factory authorized repair for the intake manifold, and replacement is required to correct the engine coolant leak and overheating issues.

 

It is not uncommon for the intake manifold and/or valve cover gaskets to develop a coolant or oil leak. Leakage from the intake manifold may result in coolant in the engine oil. Coolant mixing with the engine oil severally impacts the lubrication ability of the oil. Internal engine may result if this condition is not repaired promptly.

If you experience difficulty starting the engine when cold, stalling at idle, or hesitations during acceleration, it may be the idle air bypass valve. This valve helps the vehicle idle steady when the accelerator pedal is not pressed.

The EGR valve position (EVP) sensor can fail on this vehicle. The EVP sensor measures the EGR valve position and transmits the date to the engine control computer. If it fails, drivability and fuel economy can suffer, the Check Engine Light will commonly illuminate.

The throttle position sensor (TPS) may fail. Common symptoms of a defective TPS can be rough idle, hard starting, hesitation on acceleration, poor fuel economy, and stalling.