* Worn power steering pump: A worn pump might be delivering too much assist at higher speeds, causing the oversensitivity. This is a common issue as pumps age. You might also notice whining noises from the pump.
* Leaking power steering fluid: Low fluid levels can cause erratic behavior. Check the fluid level in the reservoir; it should be between the minimum and maximum marks. Look for leaks around the pump, hoses, and rack and pinion.
* Worn power steering rack and pinion: The rack and pinion is responsible for translating the steering wheel's movement into wheel movement. Worn components can lead to excessive play and sensitivity at speed.
* Faulty power steering pressure sensor or valve (if equipped): Some systems have sensors or valves that regulate the amount of power assist. A malfunctioning component could cause an over-boost at higher speeds. This is less common than the other issues.
* Incorrect power steering fluid: Using the wrong type of fluid can impact the system's performance. Always use the type specified in your owner's manual.
Troubleshooting Steps:
1. Check power steering fluid level: This is the easiest and first thing to do. Low fluid suggests a leak, which needs immediate attention.
2. Inspect for leaks: Carefully examine all hoses and connections for any signs of leakage.
3. Listen for unusual noises: Whining from the pump usually indicates wear. Knocking or clunking sounds might suggest issues with the rack and pinion.
4. Test at different speeds: See if the sensitivity is only at higher speeds or also present at low speeds. This helps narrow down the possibilities.
Important Note: Power steering problems can be serious and potentially dangerous. If you're not comfortable diagnosing and repairing these issues yourself, take your Grand Marquis to a qualified mechanic for inspection and repair. Driving with a faulty power steering system can make it difficult to control the vehicle, especially at higher speeds.
