Owner's Problem Description
The owner reported that after replacing a dead battery, the vehicle ran for a week before the check engine light came on, indicating misfires on cylinders 1 and 4. Following a tune-up, the car wouldn't start, leading to the replacement of ignition coils and the distributor. However, there is still no spark to start the engine, even though the engine cranks over. The owner is seeking further diagnostic advice.
Professional Technical Analysis
This 1999 Honda Prelude, equipped with a VTEC engine and automatic transmission, has experienced a series of electrical issues following a dead battery incident. Initially, after the battery was replaced, the vehicle ran for about a week before the check engine light illuminated, indicating misfires in cylinders 1 and 4. This suggests potential issues with ignition timing or fuel delivery. The owner performed a tune-up, yet the vehicle ultimately failed to start altogether. Current symptoms indicate that while the engine cranks, there is no spark present at the spark plugs, which is critical for ignition. Given the recent replacement of the ignition coils and distributor, we must consider the integrity of the ignition system wiring and the potential for a malfunctioning crankshaft position sensor or camshaft position sensor. Both sensors are crucial for proper spark timing; a failure in either can result in no spark condition. Additionally, a thorough examination of the electrical system and connections is warranted, as intermittent voltage drops or poor ground connections can also lead to this issue. The vehicle's mileage and age suggest that wiring harness degradation or corrosion at connections might be contributing factors, especially considering the previous battery issues and jump starts. Safety concerns arise as the car is unable to start, potentially leaving the owner stranded. Therefore, a methodical approach to diagnose the ignition system, including checking for voltage at the ignition coil and ensuring all grounds are clean and connected, is essential.
Possible Causes
Most common causes (ordered by frequency):
- Faulty Crankshaft Position Sensor: A malfunctioning crankshaft position sensor can fail to provide the correct engine speed and position data to the PCM, resulting in a failure to activate the ignition system. This sensor typically operates within a range of 0-5V, with a normal operating voltage around 1-2V at idle. If the sensor fails entirely, the PCM may not trigger the ignition coils, causing no spark condition. - Check engine light present, no spark at the plugs, possible stored fault code related to crankshaft position sensor.
- Ignition System Wiring Issues: Corrosion or damage in the ignition system wiring can prevent adequate voltage from reaching the ignition coils. Inspecting the wiring harness for any signs of wear, breaks, or corrosion, especially at connectors, is essential. The ideal voltage at the ignition coil should be around 12V when the ignition is on, which can be verified using a multimeter. - No voltage at the ignition coil when measured; visual inspection shows signs of wear.
- Defective Distributor Cap and Rotor: Even if the distributor is new, a faulty cap or rotor can prevent spark delivery to the plugs. The cap should exhibit no cracks or carbon tracking. The rotor must be properly aligned with the contacts within the cap. Testing continuity from the coil to the plugs can reveal issues in the distribution path. - Physical inspection shows carbon tracking on the distributor cap; continuity test shows open circuit.
- Faulty Engine Control Module (ECM): A malfunctioning ECM may not send the appropriate signals to the ignition system, leading to no spark. Checking for proper power and ground at the ECM is crucial. The ECM requires a stable voltage supply (typically 12V) and proper ground to function correctly. - No communication with the ECM, potential stored fault codes indicating ECM failure.
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 Voltage Check: Begin by checking the voltage at the ignition coil with a multimeter. Turn the ignition to the 'ON' position and verify that the voltage is approximately 12V. If there is no voltage, trace the wiring back to the ignition switch and PCM to identify any breaks or corrosion.
- STEP 2 - Check Crankshaft Position Sensor: Using a multimeter, measure the voltage output from the crankshaft position sensor while cranking the engine. The voltage should fluctuate between 0-5V. If no voltage is present or the readings are erratic, the sensor may need replacement.
- STEP 3 - Inspect Ignition System Components: Visually inspect the distributor cap and rotor for any signs of damage or wear. Ensure that they are properly seated and aligned. Test for continuity from the coil to the spark plugs to ensure the signal path is intact.
- STEP 4 - ECM Power and Ground Check: Check the power and ground connections at the ECM. Ensure the ECM is receiving a stable 12V and has a good ground connection. If the voltage is unstable or ground is missing, repair the connections and retest the ignition system.
