The vehicle may lose vehicle speed signal, which can affect speedometer operation and transmission shift quality. Most often the Vehicle Speed Sensor is faulty, however, at times, the driven gear inside the transmission is at fault. Replace the Vehicle Speed sensor and inspect the driven gear upon sensor removal.
Car problem reports
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Most reported 1994 Mercury Topaz problems
If the throttle lever is out of adjustment, or the grommets are missing / broken at the throttle or transmission, the automatic transmission can shift hard. Replace the grommets as needed and adjust the throttle lever.
Poor rubber material used in the motor mounts can cause them to fail, leading to a knocking noise or lifting sensation on acceleration. The motor mounts will need to be replaced with revised parts.
Fuel pump failure can cause the engine to crank but fail to start. Diagnosis will show insufficient, or no fuel pressure, and fuel pump in the fuel tank will need to be replaced.
Internal heater blower motor issues can cause a ticking noise from the heater blower when the fan is on. To correct this concern, replace the heater blower motor with a revised unit.
O-rings in the quick connect fittings commonly allow refrigerant to leak from the AC System. The o-rings at system quick connect fittings should be replaced.
Outdated software in the engine control processor can cause poor engine performance, hesitation on acceleration, and possible stalling problems. The processor will need to be replaced to get the updated calibration.
Sludge build up in the throttle body can cause a poor engine idle, stalling, and/or hesitation. The correction is to install a new idle air control valve spacer kit to prevent the sludge build up, set the base idle, and clean the throttle body.
A faulty Thick Film Ignition (TFI) module and stator can cause the engine to stall, and the engine may crank but not start. Replace the TFI module and stator at the distributor if diagnosis shows these to be the source of the problem.
The horn may not work sometimes. A higher than appropriate horn voltage can cause switch damage and a relay kit should be installed to moderate voltage and maintain functionality.
Pressure issues between engine and air cleaner can cause oil to collect in the air cleaner box. The PCV valve will need to be replaced.
A defective crankshaft pulley can cause a clicking, or clanging noise from the engine when it is running. The center hub can become loose and the pulley should be replaced with the revised design.
If a buzzing noise is coming from the exhaust at different engine speeds and conditions, this is commonly caused by the heat shields on catalytic converters coming loose at points. The buzzing is the metal on metal contact. Installing a large worm clamp around the catalytic converter and heat shield assembly will prevent the noise and secure the shields.