Owner's Problem Description
The owner reports that their 1999 Honda Accord with 105,000 miles typically does not start unless gas is applied. Once started, the engine runs smoothly and idles well. The vehicle has a new air filter, and the owner has checked for visible hose leaks. They suspect bad gas or issues with the fuel injectors as possible causes.
Professional Technical Analysis
The 1999 Honda Accord, equipped with a 2.3L 4-cylinder engine and approximately 105,000 miles, is exhibiting a rough starting issue where the engine fails to start without applying the throttle. This symptom suggests potential problems either within the fuel delivery system or the air intake system. Given the vehicle's age, it's plausible that the fuel system components may be deteriorating. The air filter has been recently replaced, ruling out restricted airflow as a contributing factor. One significant aspect to evaluate is the fuel pressure; a weak fuel pump or a clogged fuel filter could lead to inadequate fuel delivery, hence requiring throttle input to start the engine. Furthermore, the owner mentioned a rattling sound potentially coming from the catalytic converter, which could indicate internal damage. A failing catalytic converter can sometimes create back pressure issues that affect engine starting. This issue could also lead to abnormal exhaust emissions, possibly contributing to poor starting conditions. The vehicle currently runs fine once started, but the need for throttle input to initiate starting raises concerns about the integrity of the fuel system and potential exhaust restrictions.
Possible Causes
Most common causes (ordered by frequency):
- Fuel System Issue: The fuel pressure should be tested, ideally between 35-45 PSI while cranking. A faulty fuel pump or clogged fuel filter could lead to insufficient fuel supply, making it necessary to apply gas to initiate the start. If pressure is below 30 PSI, the pump may be weak and require replacement (OEM P/N 17040-P8A-A01, approximately $200). - Low fuel pressure readings during testing, difficulty starting without throttle input, potential fuel filter blockage.
- Throttle Position Sensor (TPS) Malfunction: If the TPS is faulty, it may not correctly send the throttle position data to the PCM, causing poor starting conditions. The expected resistance for the TPS should range from 0.5-4.5V, depending on throttle position. A faulty TPS may require replacement (OEM P/N 37840-P8A-A01, approximately $80). - Inconsistent voltage readings from TPS during cranking, possible stored codes related to TPS performance.
- Catalytic Converter Blockage: The rattling noise suggests potential internal failure of the catalytic converter, which could create back pressure and affect engine performance. A visual inspection and back pressure test should be performed. A failing cat may need replacement (OEM P/N 18220-P8A-A02, approximately $600). - Rattling noise confirmed during inspection, excessive back pressure readings during testing.
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 - Fuel Pressure Test: Using a fuel pressure gauge, check the fuel pressure at the Schrader valve located on the fuel rail. Ensure that the pressure is between 35-45 PSI while cranking. If it is below this range, inspect the fuel filter and pump for issues. This step is crucial as low fuel pressure can directly affect starting performance.
- STEP 2 - Throttle Position Sensor Check: Use a multimeter to test the TPS voltage output while slowly moving the throttle. The voltage should vary smoothly from around 0.5V at closed throttle to 4.5V at wide open. If the readings are erratic or do not fall within this range, the TPS may need replacement.
- STEP 3 - Catalytic Converter Inspection: Conduct a visual inspection of the catalytic converter for any rattling or signs of internal damage. Additionally, perform a back pressure test to ensure that the converter is not blocked. A back pressure of over 3 PSI at 2000 RPM indicates a failing cat.
- STEP 4 - Road Test with Monitoring: After repairs or tests, perform a controlled road test while monitoring the vehicle's performance. Pay particular attention to the starting procedure and whether the vehicle requires throttle input to start. This will help confirm if the issue has been resolved.
