Owner's Problem Description
The owner of the 1991 Ford Probe reported that while driving, the engine shut off unexpectedly. Upon inspection, oil was found spilled under the hood, and the oil level was low. After adding several gallons of oil, the vehicle restarted and ran for about 10 minutes before shutting off again. Now, it cranks but will not start. The owner is seeking assistance to diagnose the issue.
Professional Technical Analysis
The 1991 Ford Probe, equipped with a 2.0L 4-cylinder engine, has an estimated mileage of around 150,000 miles. The owner reported that the vehicle experienced an unexpected shutdown while driving, followed by a significant oil leak. After adding oil, the vehicle restarted but failed after a short drive. The current condition shows that the engine cranks but fails to start. This situation warrants a comprehensive diagnostic approach, starting with fuel delivery and ignition system checks. Since the owner reported no sound from the fuel pump during ignition, the fuel pump circuit, including the inertia switch and fuel pump relay, should be examined. Additionally, oil leaks could indicate potential internal engine issues, such as a blown head gasket or low oil pressure, which may affect the engine’s ability to start. The fuel system should be tested for proper fuel pressure, ideally within the range of 30-40 PSI, and the ignition system must be verified for spark presence. In this case, addressing the fuel system first is critical due to the lack of pump activation, and further inspection of the oil leak sources is needed to prevent future failures.
Possible Causes
Most common causes (ordered by frequency):
- Fuel Pump Failure: The fuel pump may not be operating, indicated by the absence of sound during the ignition process. The fuel pump relay or inertia switch could be faulty. The fuel pump should provide a pressure of 30-40 PSI for proper engine operation. A multimeter can be used to check for voltage at the fuel pump connector when the ignition is turned on. If no power is present, inspect the relay and inertia switch. - No sound from the fuel pump when the ignition is turned on, absence of fuel pressure at the fuel rail, potential diagnostic trouble codes related to the fuel system.
- Ignition System Malfunction: The ignition system may not be providing spark, which is critical for starting. This includes checking the ignition coil, spark plugs, and associated wiring. A simple test with a spark tester can confirm if the ignition system is functioning correctly. If there's no spark, components such as the ignition control module should be tested. - Engine cranks without starting, possible stored codes for ignition system components, no spark detected during testing with a spark tester.
- Oil Pressure Issues: The presence of oil leaks suggests potential oil pressure problems, which can lead to engine shutdowns. If the oil pressure is too low, it can prevent the engine from starting. A manual oil pressure gauge should be used to measure the oil pressure, which ideally should be between 10-20 PSI at idle. - Visible oil leaks under the hood, potential low oil pressure indicated by gauge or warning lights, engine shutdowns due to oil pressure drops.
- Electrical Connection Issues: Poor electrical connections, especially at the fuel pump and ignition components, can lead to intermittent failures. Corrosion or loose connections should be inspected, and the integrity of the wiring harness should be checked for damage. A visual inspection and multimeter testing can identify issues in the wiring. - Corroded connectors, loose wiring at the fuel pump or ignition module, intermittent starting issues in the past.
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 - Initial Visual Inspection: Begin with a thorough visual inspection under the hood to identify any obvious signs of oil leaks, damaged wiring, or loose connections. Ensure that the oil level is within specifications and check for any visible signs of fuel leakage. This step lays the groundwork for further diagnostics.
- STEP 2 - Fuel Pump Operation Check: Turn the ignition key to the ON position without cranking the engine and listen for the fuel pump activation sound. If no sound is heard, use a multimeter to check for voltage at the fuel pump connector. If voltage is present, the fuel pump may be faulty and should be replaced (OEM part number: F1CZ-9345-A).
- STEP 3 - Ignition System Testing: Remove a spark plug and connect a spark tester to check for spark. Crank the engine and observe the spark tester for any spark presence. If no spark is present, test the ignition coil, wires, and control module for proper operation. This step is crucial in determining if the ignition system is functioning properly.
- STEP 4 - Oil Pressure Measurement: If the engine cranks but does not start, check the oil pressure using a manual gauge. Connect the gauge to the oil pressure sender unit and start the engine. The oil pressure should be within the range of 10-20 PSI at idle. If the pressure is low, further investigation into oil pump function or internal engine issues is required.
