Owner's Problem Description
The owner recently purchased a 2002 Toyota Celica equipped with a VVT-i engine and is experiencing a severe misfire. They noted that disconnecting any spark plug wire results in the engine stalling, similarly for the fuel injectors, except for cylinder number two, which shows no change even after swapping injectors. The vehicle's condition indicates a significant performance issue needing further investigation.
Professional Technical Analysis
The 2002 Toyota Celica with a VVT-i engine is exhibiting a severe misfire condition, particularly involving cylinder number two. With an estimated mileage of around 120,000, initial diagnostics reveal that disconnecting the spark plug wires results in engine stalling, but cylinder two shows no change upon injector swapping. This suggests a potential issue with either the ignition system or the fuel delivery to that specific cylinder. Diagnostic codes retrieved indicate problems with the camshaft position sensor and throttle position sensor; however, both sensors have been verified as functional. Given that compression tests return normal values, it’s crucial to investigate the electrical signals to the injector and spark plug, as well as to verify the absence of fuel delivery issues. The VVT-i system's operation can also affect fuel metering, further complicating the diagnosis if it malfunctions. The next steps should include checking the injector pulse using a noid light to confirm that the ECU is providing the correct signal, and performing a thorough inspection of the ignition system voltage with an oscilloscope to analyze the spark timing and strength. This analysis will help identify whether the misfire is due to a lack of fuel or spark in cylinder two, which could also point to wiring issues or faulty connections in the system.
Possible Causes
Most common causes (ordered by frequency):
- Ignition System Voltage Issue: The ignition system may be failing to deliver adequate voltage to the spark plug in cylinder two, leading to misfires. Use an oscilloscope to verify the ignition voltage during cranking and at idle. Expected spark voltage should be around 12V for proper firing. A malfunctioning ignition coil or deteriorating wiring could cause low voltage, affecting the spark quality. Check resistance in the ignition coil (should be between 0.5-1.5 ohms primary, 6,000-15,000 ohms secondary) and inspect connectors for corrosion or loose connections. - Engine misfire on cylinder two, oscilloscope voltage readings show low peaks, corrosion found at ignition coil connector.
- Fuel Delivery Problem: There may be an issue with the fuel injector for cylinder two, despite swapping the injector showing no improvement. This could indicate an electrical issue, such as a faulty injector driver circuit from the PCM. Use a noid light to confirm the injector is receiving the correct pulse from the PCM. Fuel pressure should be checked and must remain between 35-45 PSI. If pressure is low, check the fuel pump operation and filter condition. - Noid light test shows no pulse to injector two, fuel pressure gauge reading below 30 PSI, indicating possible pump failure.
- VVT-i System Malfunction: A malfunction in the VVT-i system could lead to improper timing and fuel delivery, particularly affecting cylinder two. The VVT-i actuator should be inspected for functionality, and the camshaft position sensor should be tested for accurate signal output. The expected voltage output from the camshaft position sensor should be around 0.5-4.5V depending on the engine load. Any deviation could indicate a fault in the VVT system. - Camshaft position sensor output voltage measured at 0.2V, indicating a possible sensor fault, VVT actuator response sluggish 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 - Initial OBD-II Scan: Start with a thorough scan of the vehicle using an OBD-II scanner or GeekOBD APP to retrieve any stored trouble codes. Pay attention to any codes related to the camshaft and throttle position sensors. Analyze freeze frame data for additional context on the conditions when the fault occurred. This step is crucial to determine if there are any underlying issues affecting the engine's performance.
- STEP 2 - Voltage and Pulse Testing: Use an oscilloscope to check the ignition coil output voltage and the injector pulse width for cylinder two. Verify that the ignition voltage peaks at around 12V during cranking and check the injector pulse width, which should be around 2-3 ms at idle. Use a noid light to confirm the injector is receiving the correct signals from the PCM. Document any anomalies in the readings to assist in diagnosing the problem.
- STEP 3 - Fuel Pressure Check: Inspect the fuel pressure at the rail to ensure it meets specifications (35-45 PSI). If the pressure is low, check the fuel pump operation and the condition of the fuel filter. Verify that the fuel lines are not kinked or blocked. Address any issues found during this inspection before proceeding further.
- STEP 4 - VVT-i System Examination: Inspect the VVT-i actuator and camshaft position sensor. Use the oscilloscope to verify the sensor's output voltage during various engine loads. Ensure that the actuator is responding correctly to changes in engine speed and load. Document findings for potential further evaluation or repairs required for the VVT system.
