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Mercury Problems

RepairPal has identified the most common problems for 16 Mercury models 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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146
Known Problems

Various problems with the 5-speed automatic transmission were common. These problems can be more common on the 2002 models with build dates before March, 2002. There are many service bulletins describing the diagnoses and repairs, which include fluid leak repairs, transmission software updates, or internal failures requiring a costly repair.

If the key will not come out of ignition, this may be related to problems with the shifter knob sticking and / or binding of the shifter bezel. Replace the shifter knob and / or shifter bezel as needed.

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.

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.

 

The heater hose outlet may leak coolant at the back of the intake manifold. Sometimes this is misdiagnosed as a leaking intake manifold gasket because it resembles a leaking manifold.

Transmission problems are common in this model, often as a result of a failed front pump. The pump loses its ability to create hydraulic pressure, which an automatic transmission needs to function. A sign of front pump failure can be a whine type noise.

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 automatic transmission may develop shifting concerns. On lower mileage vehicles, upgrading the software in the powertrain control module (PCM) and the transmission control module (TCM) may correct the problem. As the mileage increases, internal transmission damage can occur. Repairs could involve replacement of the valve body or a complete transmission rebuild. Whenever major transmission repairs are made, it is important to be sure the PCM and the TCM have the latest software updates to help prevent these issues from reoccurring.

Transmission problems are common in this model, often as a result of a failed front pump. The pump loses its ability to create hydraulic pressure, which an automatic transmission needs to function. A sign of front pump failure can be a whine type noise.

Bad spark plugs or an ignition coil can cause ignition misfire, which will illuminate the Check Engine Light.

A rattling noise from the engine may indicate that the timing chain cassette is worn. Our technicians tell us that installing an updated cassette and timing chain tensioner should correct this concern.

The Check Engine Light can illuminate with codes due to the lack of EGR (exhaust gas recirculation) flow caused. This is commonly a result of a clogged passage in the intake manifold. To correct this problem, the EGR valve has to be removed and the passage cleaned thoroughly. Partial restriction of this passage can cause smog test failures for the NOx emissions without causing a drivability symptom.

The Mercury Grand Marquis 4.6L V8 engine is known for displaying the normal symptoms of a coolant leak, including overheating, especially when the vehicle is idling, the strong smell of coolant from the engine, and illumination of the low engine coolant warning light

This leak is difficult to locate as it is buried underneath the intake manifold, and only begins to leak coolant onto the ground in advanced stages of disrepair. This leak springs from the heater tube, which allows coolant to flow between the water pump and HVAC heater core

When the connection for this tube begins to leak, the coolant burns on the hot engine, and produces a sweet smell that is unmistakably engine coolant. 

The remedy can be complicated, and will necessitate removal of the intake manifold, heater tube, and possibly the water pump. After removal of these items, the connector may be replaced, or a set of o-rings, depending on the year of the vehicle. Most vehicles, model 2002 and later, will have o-rings, and the water pump will not need to be removed. 

Looseness in the steering shaft and steering shaft coupling U-joint can cause a knocking / popping noise from the steering column when turning. The steering shaft and coupling U-joint will need to be replaced.

The engine may overheat at idle when the AC is on. A new, upgraded fan motor and resistor may be required to correct this concern.