Owner's Problem Description
The owner reports that their 2002 Toyota Landcruiser occasionally cranks but fails to start, with occurrences happening at least once a month. The vehicle will start unexpectedly after 2-3 days of not starting. Fuel pressure from the filter was confirmed to be fine, but there is no spark during these incidents. Previous checks included verifying flow from the fuel filter.
Professional Technical Analysis
The 2002 Toyota Landcruiser, equipped with a 4.7L V8 engine and an automatic transmission, has approximately 149,000 miles. The owner describes an intermittent no-start condition where the engine cranks but fails to fire. Symptoms typically manifest after the vehicle sits for a couple of days. Initial diagnostic steps confirmed adequate fuel delivery from the filter, suggesting that fuel pressure is sufficient. However, the absence of spark indicates potential ignition system failures. Given the age and mileage of the vehicle, common failure points include the ignition relays, crankshaft position sensor (CKP), and camshaft position sensor (CMP). Both sensors are critical for the Engine Control Module (ECM) to determine the correct ignition timing. If either sensor fails to provide the necessary signal due to thermal breakdown or electrical issues, the vehicle will crank but not start. The ignition relay functionality should be tested, as well as the voltage supply to the sensors, to ensure they are operational. Considering the intermittent nature of the problem, thermal expansion or contraction could be affecting sensor performance. Additionally, inspection of the wiring harness for wear or damage is essential, as this can lead to intermittent faults. Safety concerns include the potential for stalling while driving if the system fails unexpectedly. Technical observations suggest that the CKP and CMP sensors often fail in these models around the 100,000-mile mark due to heat exposure in the engine bay. Proper voltage should be around 5V for both sensors and proper gap settings should be validated. Diagnostic tools such as a multimeter for voltage checks and an oscilloscope to monitor sensor signals are recommended.
Possible Causes
Most common causes (ordered by frequency):
- Ignition Relay Failure: The ignition relay located in the underhood junction box may be failing to supply power to the ignition system intermittently. This could cause the system to not receive power, resulting in a no-spark condition. Relay should be tested for continuity and proper voltage under load conditions. - No power to ignition coils when cranking, potential relay clicking noise, visual inspection shows signs of corrosion.
- Crankshaft Position Sensor Failure: The CKP sensor may be malfunctioning, particularly if it exhibits thermal failure symptoms. This sensor is critical for the ECM to determine engine position and timing. It should have a resistance value between 200-1,000 ohms and produce a waveform when cranking. - Intermittent waveform signal when cranking, resistance check indicates values outside specified range, stored DTCs related to CKP.
- Camshaft Position Sensor Failure: Similar to the CKP, the CMP sensor failure could cause the ignition system to not receive the correct timing signal, leading to a no-start condition. Check for proper voltage supply and signal integrity. - No signal detected at CMP during cranking, visual inspection shows signs of wear, and continuity check fails.
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: Use the GeekOBD APP to perform a comprehensive scan for stored trouble codes and freeze frame data. Look for any fault codes related to the ignition system, CKP, or CMP. Document any codes present, as they can provide clues to the underlying issue.
- STEP 2 - Voltage and Continuity Checks: Check the ignition relay for proper operation. Measure the voltage at the relay and ensure it receives power when the key is in the 'ON' position. Perform continuity tests on the CKP and CMP sensors to verify they are functioning correctly.
- STEP 3 - Signal Monitoring: Use an oscilloscope to monitor the CKP and CMP signals while cranking the engine. Both sensors should produce a consistent waveform. If the signal is weak or absent, further investigation into the sensors and wiring is warranted.
- STEP 4 - Fuel Pressure Verification: Even though fuel flow was observed from the filter, measure the actual fuel pressure at the fuel rail. It should be within the specified range of 35-45 PSI. Insufficient pressure can lead to no-start issues even if fuel is present.
