Owner's Problem Description
The owner reports that the 1992 Buick Century Limited starts fine but experiences jerking during driving, followed by the temperature light turning on before the engine dies. It can restart by itself when gas is released, but the issue persists despite replacing several components including spark plug wires, idle air valve, mass air flow sensor, spark plugs, and the number 5 injector. The owner seeks assistance in diagnosing the problem.
Professional Technical Analysis
The 1992 Buick Century Limited is equipped with a 3.8L V6 engine and is likely experiencing issues related to the fuel delivery or ignition systems. Given the reported symptoms of jerking and stalling, it is crucial to analyze the vehicle's fuel pressure and ignition timing during operation. The check engine light's intermittent behavior indicates potential fault codes that need to be retrieved. Historical repair records show that components such as the idle air control valve and mass air flow sensor are common failure points; however, since these have been replaced, attention should now shift to the fuel pump and related circuitry. The vehicle may also exhibit electrical issues, particularly if there are fluctuations in voltage due to a failing alternator (ideal voltage should be between 13.8-14.4V under load). The engine stalling could be linked to a failing crankshaft position sensor, which can cause erratic engine behavior when hot. It's essential to monitor live data for fuel pressure (expected 35-45 PSI) and check for any abnormal resistance in the ignition circuit (should be between 0.5-1.5 ohms at ignition coil). The current condition shows the vehicle is not reliable for driving, posing safety concerns.
Possible Causes
Most common causes (ordered by frequency):
- Fuel Pump Failure: Insufficient pressure from the fuel pump, which should maintain 35-45 PSI, can lead to poor fuel delivery, causing the engine to jerk and stall. Common failure mode includes a worn electric motor or clogged fuel filter. - Intermittent stalling, poor acceleration, and fluctuating fuel pressure readings during diagnostic checks.
- Crankshaft Position Sensor Malfunction: A failing crankshaft position sensor can cause erratic engine performance, particularly when hot. This sensor is critical for proper ignition timing and fuel delivery. - Check engine light may illuminate with related fault codes (e.g., P0335), poor engine performance when hot, and intermittent stalling.
- Ignition System Failure: Issues within the ignition system, such as coil failure or poor connections, can lead to misfires and stalling. Resistance values of ignition components should be checked. - Poor engine response, misfires, and irregular voltage readings on ignition coils during testing.
- Electrical Connection Issues: Corroded or loose electrical connections can cause voltage fluctuations that affect engine performance. Inspecting grounds and connectors for corrosion is essential. - Intermittent electrical issues, poor starting, and erratic behavior of electrical accessories.
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 Retrieval: Start with a thorough scan using an OBD-II scanner or the GeekOBD APP to retrieve any stored fault codes. Pay attention to any codes related to the crankshaft position sensor or fuel system. Freeze frame data can provide insights into conditions at the time of the fault occurrence.
- STEP 2 - Fuel Pressure Testing: Check fuel pressure using a fuel pressure gauge connected to the fuel rail. The pressure should be within 35-45 PSI when the ignition is on and the engine is running. If pressure is low, inspect the fuel pump and filter for blockages.
- STEP 3 - Live Data Monitoring: Utilize the GeekOBD APP to monitor live data such as fuel trim values, MAP sensor readings, and ignition timing. These parameters can help diagnose issues related to fuel delivery and ignition.
- STEP 4 - Electrical Connection Inspection: Inspect all relevant electrical connections, including grounds and connectors for corrosion. Ensure that voltage readings are stable during operation, particularly at the ignition coil and fuel pump.
