Owner's Problem Description
The owner reports that the 2003 Ford Taurus starts fine when cold but fails to start after being turned off for a short period, such as when running errands. The engine turns over but does not start. This issue has occurred multiple times, suggesting a possible intermittent fault either in the fuel delivery system or the ignition system.
Professional Technical Analysis
The 2003 Ford Taurus, equipped with a 3.0L V6 engine and approximately 120,000 miles on the odometer, is showing symptoms of intermittent no-start conditions after brief stops. When the vehicle is cold, it starts normally, but after being shut off, it will crank without starting. This issue can often be attributed to several possible causes. First, a failing fuel pump or clogged fuel filter could prevent adequate fuel pressure from reaching the engine. The fuel pressure should be between 30-45 PSI when the key is turned to the 'ON' position, but if it drops below this threshold, the engine may not start. Second, ignition system issues such as a malfunctioning ignition coil or a faulty crankshaft position sensor could lead to no spark during cranking. The PCM (Powertrain Control Module) relies on a stable input from various sensors, and if the crankshaft position sensor is failing, it might not send the necessary signals to the ignition system. Additionally, after the vehicle sits for a short time, thermal expansion could affect electrical connections or components, leading to intermittent faults. Safety concerns arise as this no-start condition could leave the driver stranded. A thorough diagnostic review of the fuel and ignition systems is recommended, including checking fuel pressure and spark availability with a tester to confirm operation during the non-start condition.
Possible Causes
Most common causes (ordered by frequency):
- Fuel Pump Failure: The fuel pump may fail to maintain the necessary pressure due to wear or electrical faults, leading to insufficient fuel delivery. Pressure should be 30-45 PSI during the initial ON position, but intermittent failures can cause drops below this level when warm. - Inconsistent fuel pressure readings, engine cranks but does not start, potential fuel smell during cranking.
- Ignition Coil Malfunction: A failed ignition coil can prevent the engine from starting, especially if it is heat-soaked. Testing spark at the plugs can confirm if the ignition system is functioning correctly. - No spark detected at the plugs, engine cranks without starting, possible stored fault codes related to ignition.
- Crankshaft Position Sensor Failure: A malfunctioning crankshaft position sensor can disrupt the timing for fuel injection and ignition, preventing the engine from starting. The sensor should provide a stable signal to the PCM. - Engine cranks without starting, possible codes indicating sensor failure, intermittent operation after cooling.
- Thermal Expansion Effects: Electrical connections may expand when heated, causing intermittent contact issues, particularly in connectors or wire harnesses related to the ignition or fuel system. - No start after heat soak, intermittent issues that resolve after cooling down, visible corrosion or wear on connectors.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - OBD-II Code Scan: Begin with a thorough OBD-II scan using the GeekOBD APP to retrieve any stored fault codes. This can provide insight into issues with the engine management system and help isolate the problem.
- STEP 2 - Fuel Pressure Test: Connect a fuel pressure gauge to the fuel rail and check the pressure with the ignition on. Ensure the pressure is within the specifications of 30-45 PSI. If pressure drops below this, the fuel pump or filter may be the issue.
- STEP 3 - Spark Test: Remove a spark plug and connect a spark tester. Crank the engine while observing for spark. If no spark is present, the ignition coil or related components may need further evaluation.
- STEP 4 - Crankshaft Position Sensor Check: Measure the output voltage of the crankshaft position sensor while cranking the engine. The voltage should fluctuate correctly; if not, the sensor may be faulty.
