Owner's Problem Description
The owner reports that their 1986 Toyota Camry lost power while driving, began bucking, and then died without restarting. Previous checks included relays, a new distributor, igniter, cap, rotor, and wires, with all resistance and voltage within operational limits. They have followed the Haynes manual for diagnostics and consulted with a dealership technician. The car is their only transportation, and they urgently need assistance.
Professional Technical Analysis
This 1986 Toyota Camry is experiencing a no-spark condition, which can be attributed to multiple interconnected systems. The vehicle is equipped with a 2.0L engine and has likely accumulated around 150,000 miles. The symptoms began with a loss of power while driving, followed by bucking before the engine stalled. The owner has replaced various components including the distributor, igniter, cap, rotor, and spark plug wires, suggesting that the ignition system has been comprehensively addressed. However, the presence of no spark indicates a possible failure in the signal generation from the crankshaft or camshaft position sensors, which are integral to the distributor assembly. The retrieved codes (6 and 11) suggest issues with these sensors and potentially point towards a failure in the Engine Control Unit (ECU) if no spark is present despite proper fuel pressure. The investigation must focus on the integrity of the ignition system, particularly the distributor's position sensors, as well as ensuring that the main EFI fuse is intact and functioning. In my experience with similar vintage Toyota models, intermittent failures in the ignition system can often be traced back to poor connections or sensor failures, especially as the vehicle ages. Current troubleshooting must prioritize verifying the distributor's sensor performance and ensuring the ECU is receiving the correct inputs for ignition timing. If the ECU has been replaced and spark is still absent, further diagnostic testing with an oscilloscope may be required to assess the signals from the crank and cam sensors during cranking.
Possible Causes
Most common causes (ordered by frequency):
- Crankshaft Position Sensor Failure: This sensor is crucial for the ECU to determine ignition timing. A malfunction can result in no signal being sent to the igniter, leading to a no-fire condition. Typical symptoms include no spark at the plugs. Testing should include checking the sensor resistance (should be within 200-1,000 ohms) and verifying the signal at the ECU connector during cranking. - No spark at plugs, stored code 6 indicating a potential crankshaft position sensor issue.
- Camshaft Position Sensor Issue: Similar to the crankshaft sensor, this component is also part of the distributor assembly. If it fails, the ECU does not receive the necessary information to trigger the ignition system. Resistance checks should be conducted, and if the sensor shows intermittent operation, it may need replacement. - Intermittent starting issues, stored code 11 indicating a camshaft position sensor fault.
- Defective Engine Control Unit (ECU): If the ECU is damaged, it may fail to process signals from the crank and cam sensors, leading to a no-fire condition. Testing with a known good ECU can confirm this. Look for signs of water damage or previous repairs on the unit. - No response from ECU during testing, all other components functioning correctly.
- Faulty EFI Fuse: A blown EFI fuse can disrupt the power supply to the ignition system and fuel injectors. Ensure that the fuse is not only visually inspected but also tested with a multimeter for continuity. - Insurance fuse blown, not properly tested, which could cause power interruptions.
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 Code Retrieval and Inspection: Use GeekOBD APP or a compatible OBD-II scanner to retrieve fault codes. Document any codes present, particularly those related to the crankshaft (Code 6) and camshaft position sensors (Code 11). Inspect all connectors for corrosion or damage, especially at the ECU and distributor.
- STEP 2 - Sensor Testing: Check the crankshaft and camshaft position sensors for proper resistance and output signals. Resistance should be within 200-1,000 ohms for the crank sensor. Use the GeekOBD APP to monitor the live data while cranking to ensure the signals are present during engine operation.
- STEP 3 - ECU Functionality Check: If the sensors are functioning correctly, test the ECU with a known good unit, ensuring all connections are secure. Monitor for any changes in fault codes or spark availability. This step is crucial to confirm if the ECU is the source of the problem.
- STEP 4 - System Power Integrity: Verify the integrity of the EFI fuse and associated wiring. Check for continuity with a multimeter and ensure no shorts or open circuits are present. This step can prevent undiagnosed power issues affecting the ignition system.
