Owner's Problem Description
The owner of a 1991 Acura Integra GS reports that the vehicle starts and runs for a short period before stuttering and eventually stalling. After it dies, it will not restart until it cools down. Despite replacing the spark plugs, ignition control module, ignition rotor, and main relay (from rz-0067 to rz-0063), the owner has been unable to retrieve any trouble codes. The vehicle has spark at the wires, but the exact cause of the problem remains unidentified.
Professional Technical Analysis
This 1991 Acura Integra GS, equipped with a 1.8L DOHC engine and approximately 200,000 miles, exhibits symptoms of stalling after reaching operating temperature. The owner described that once the engine warms up, it begins to stutter before ultimately stalling and failing to restart until cool. Given the extensive parts replacement, the issue may stem from thermal-related failures in components that are not generating a fault code. Notably, the replacement of the ignition control module (ICM) is commendable, as thermal failures are common in these models, often leading to intermittent faults when the engine reaches high temperatures. Testing the ICM under these conditions is critical, as it may exhibit failure once the temperature exceeds 200°F. Additionally, the main relay (replaced by rz-0063) should also be inspected, as these relays can fail under heat, leading to fuel pump or ignition cutoff. Fuel delivery should be assessed by checking the fuel pressure during engine operation, ideally maintaining 30-40 PSI. A malfunctioning fuel pump may not produce adequate pressure when hot, leading to stalling. Observing the vehicle’s behavior during these thermal events, including monitoring for spark integrity, fuel pressure, and ICM function with a diagnostic tool such as GeekOBD APP, will yield insights into the root cause.
Possible Causes
Most common causes (ordered by frequency):
- Ignition Control Module (ICM) thermal failure: The ICM may fail when hot, common in older Acura models. When the engine reaches a certain temperature, the heat can cause the semiconductor components in the ICM to malfunction, leading to a loss of spark. Testing the ICM with a heat gun can reveal if it fails under heat conditions. Voltage supply to the ICM should be stable at 12V during operation. - No start when hot, intermittent stalling, ICM replacement without improvement.
- Fuel Pump Failure: As the vehicle heats up, the fuel pump could be overheating and shutting down due to thermal overload. Checking for fuel pressure during stalling events is crucial; the pump should maintain 30-40 PSI. If the pressure drops significantly, the pump may need replacement (OEM P/N 17040-P72-004). - Low fuel pressure during hot operation, potential overheating of the fuel pump.
- Main Relay Failure: The main relay (rz-0063) can fail under heat, cutting off power to the fuel pump or ignition system. Testing the relay for continuity and proper function when hot is essential, as they often fail due to thermal stress. - Intermittent power loss symptoms, relay replacement not resolving the issue.
- Distributor Cap Failure: A hairline crack in the distributor cap can expand when hot, causing misfires and stalling. Inspecting the cap for cracks and ensuring a good connection to the rotor is vital for proper ignition. - Visual inspection shows potential cracks, stuttering occurs under heat.
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 by using the GeekOBD APP to perform a comprehensive scan, focusing on any pending codes or freeze frame data. Given the owner's report of no codes, it is essential to monitor live data during operation to capture any intermittent faults that may arise as the engine heats up.
- STEP 2 - Fuel Pressure Testing: Install a fuel pressure gauge to the fuel line and monitor pressure during engine operation, especially when stalling occurs. The pressure should maintain between 30-40 PSI. If the pressure drops significantly during warm operation, further investigation of the fuel pump and relay is warranted.
- STEP 3 - ICM and Relay Testing: After confirming fuel pressure is adequate, proceed to test the ICM and main relay. Check the ICM for proper voltage supply while running hot and verify relay function under similar conditions using a multimeter.
- STEP 4 - Distributor Cap Inspection: Finally, inspect the distributor cap for any signs of cracks or wear. A visual inspection can reveal potential issues that might not trigger fault codes but can significantly impact engine performance when hot.
