Owner's Problem Description
The owner of a 1988 Oldsmobile Delta 88 reports that the vehicle shuts off after running for a while. The engine stalls as if the key has been turned off, and it won't restart for several hours. The owner has replaced the ECM, cam and crank sensors, and the electronic distributor pack. Despite these efforts, the issue persists, and the ignition module has been tested and deemed functional. The owner is seeking assistance as they feel lost with the ongoing problem.
Professional Technical Analysis
The 1988 Oldsmobile Delta 88, equipped with a 3.8L V6 engine and an automatic transmission, has a reported issue where the engine shuts off after a period of operation, typically once it reaches operating temperature. The vehicle has approximately 120,000 miles on it. The owner has undertaken significant repairs, including replacing the engine control module (ECM), camshaft and crankshaft position sensors, and the electronic distributor pack. Despite these replacements, the vehicle continues to experience stalling, with no spark present when the engine fails to start. Upon further investigation, it's crucial to assess the function of the ignition system, particularly the ignition module integrated within the distributor. A known issue with this model is the heat-related failure of the ignition module, often causing intermittent stalls when the engine is hot. Moreover, the absence of the crankshaft position sensor magnet could contribute to erratic sensor readings, although its role is often debated. The vehicle's current condition raises safety concerns due to unexpected stalling, which can occur in traffic. A comprehensive examination of the ignition system, including voltage checks (the ignition module should operate with stable inputs of 12V+), and testing the integrity of the wiring harness connected to the ignition components is advised. The PCM should be monitored for any stored DTCs (Diagnostic Trouble Codes) that could provide insight into the failure mode, particularly codes related to the ignition system, such as P0335 (Crankshaft Position Sensor Circuit). The vehicle's wiring and connections should also be inspected for any signs of corrosion or damage, as this could lead to intermittent faults.
Possible Causes
Most common causes (ordered by frequency):
- Ignition Module Thermal Failure: The ignition module, which is critical for providing spark at the correct timing, may fail when subjected to high temperatures, common in the 1988 Oldsmobile Delta 88. This module can exhibit normal function when cool but fails to produce spark once the engine heats up, leading to stalling. It is advisable to check module temperatures during operation. - Check engine light may illuminate, no spark detected during overheating, possible stored codes related to ignition timing.
- Crankshaft Position Sensor Absence of Magnet: The crankshaft position sensor relies on a magnet to detect the position of the crankshaft accurately. If the magnet is missing, it can lead to intermittent signal issues, causing the engine to stall unexpectedly. While some may believe the absence doesn’t cause problems, real-world experience suggests otherwise. - Engine stalling with no crank signal, potential misalignment of the sensor, and erratic engine performance.
- Intermittent Wiring Issues: Poor connections or damaged wiring within the ignition system can cause intermittent failures, particularly under heat conditions. Corroded or frayed wires leading to the ignition module can disrupt the signal path, preventing the engine from starting. Wiring integrity should be assessed carefully. - Visual inspection may reveal damaged insulation, intermittent connectivity during heat, and related faults.
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 OBD-II Diagnosis: Begin with a scan using a professional OBD-II scanner or GeekOBD APP to retrieve any stored codes. Pay particular attention to codes related to the ignition system such as P0335. Additionally, check freeze frame data to capture the conditions under which the stall occurred.
- STEP 2 - Live Data Monitoring: Use GeekOBD APP to monitor live data, focusing on the crankshaft position sensor signal and ignition timing parameters. Observe the vehicle’s temperature and any fluctuations in the ignition system voltage while the engine is running. This can help identify whether the ignition module is failing under heat conditions.
- STEP 3 - Component Testing: Test the ignition module and crankshaft position sensor for functionality. This includes checking the resistance of the ignition module (should be within manufacturer specifications) and verifying that the sensor is correctly positioned and functioning. The expected resistance for the module should be between 0.5-2.0 ohms.
- STEP 4 - Wiring Inspection: Conduct a thorough inspection of the wiring harness associated with the ignition system. Look for signs of wear, corrosion, or loose connections that could lead to intermittent failures. Use a multimeter to check for continuity and proper voltage at the ignition module under various conditions.
