Owner's Problem Description
The owner reports that their 1988 Subaru GL10 wagon, equipped with an 1800cc OHV SPFI engine, initially ran fine but has recently experienced starting issues. After trouble starting, it would sometimes start on the next attempt but fails to start again upon switching off the ignition. Previous maintenance includes new plugs, but the wires, cap, and rotor are about a year old. The owner is seeking assistance to diagnose the no-spark condition.
Professional Technical Analysis
The 1988 Subaru GL10, powered by an 1800cc OHV SPFI engine and with an estimated mileage around 200,000 miles, presents a no-spark issue following intermittent starting difficulties. The engine cranks but fails to ignite. Common causes of no-spark conditions in this model include failures in the ignition system, particularly the ignition coil, distributor cap, rotor, and associated electrical connections. Given the vehicle's age, the integrity of the ignition wiring is also a concern, especially if subjected to environmental stressors such as moisture or corrosion. The ignition coil should produce approximately 12-15 kV output under load, while the distributor cap and rotor should be free of carbon tracking or excessive wear. A thorough inspection of the primary (battery voltage) and secondary (spark plug voltage) circuits is crucial. Additionally, the presence of a check engine light and any stored trouble codes should be evaluated via OBD-I diagnostics to confirm any underlying issues that may affect the PCM's operation. This vehicle's electrical system should maintain 12V at the ignition coil when cranking. If proper voltage is present but no spark is generated, further testing of the coil resistance (should be within 0.5-1.5 ohms) and the pickup coil resistance (should range between 500-1500 ohms) is warranted. Safety is paramount; ensure all testing is performed with the ignition off to prevent short circuits or accidental shocks.
Possible Causes
Most common causes (ordered by frequency):
- Ignition Coil Failure: The ignition coil may have failed, preventing sufficient voltage from reaching the spark plugs. A typical coil output voltage should be around 12-15 kV under load. Testing the coil's primary resistance should yield a reading of 0.5-1.5 ohms. If the coil is faulty, it should be replaced with an OEM part (e.g., P/N 22433AA310). - No voltage at spark plug wires during cranking, rough or absent spark when tested directly from the coil, possible stored fault codes related to ignition.
- Distributor Cap and Rotor Issues: Inspect the distributor cap and rotor for signs of carbon tracking or wear. These components should have no visible cracks or carbon buildup. A faulty cap or rotor can disrupt the signal to the ignition coil, leading to a no-spark condition. Replacement with OEM parts (e.g., cap P/N 22141AA030, rotor P/N 22141AA010) is recommended. - Visual inspection shows wear on cap/rotor, intermittent spark when tested, potential arching or carbon tracking visible.
- Electrical Connection Issues: Corroded or loose electrical connections within the ignition system can lead to intermittent spark delivery. Inspect all related wiring and connectors, especially around the ignition coil and distributor. Ensure tight and corrosion-free connections, as poor connections can lead to voltage drops and failed ignition. - Loose connections observed during inspection, voltage drops noted when testing with a multimeter, potential shorts found in wiring harness.
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 Electrical System Check: Start with a thorough visual inspection of all ignition system components, including the ignition coil, distributor cap, rotor, and associated wiring. Look for signs of wear, corrosion, or loose connections. Use a multimeter to check for voltage at the ignition coil while cranking; it should maintain around 12V. If voltage is present but no spark, the coil likely needs testing.
- STEP 2 - Ignition Coil Testing: Test the ignition coil by measuring the primary and secondary resistance. Primary resistance should be between 0.5-1.5 ohms, while secondary output voltage should be 12-15 kV. If readings are out of spec, replace the coil with OEM part number 22433AA310. Ensure all connections are secure before retesting.
- STEP 3 - Distributor Cap and Rotor Inspection: Remove the distributor cap and rotor to inspect for any signs of wear or damage. Look for carbon tracking, cracks, or excessive buildup. Replace as needed with OEM parts (cap P/N 22141AA030, rotor P/N 22141AA010). Ensure proper alignment when reinstalling.
- STEP 4 - Electrical Connections Verification: Inspect all related electrical connections for corrosion or looseness. Use dielectric grease on connectors to prevent future corrosion. Retest the ignition system to ensure all components are functioning correctly and that spark is delivered to the plugs.
