Owner's Problem Description
The owner reports that their 1990 Mazda RX-7 with a 1.3L engine and 170,000 miles will not start, despite having fuel and spark. The battery is fully charged. The problem is intermittent; sometimes it will fire up but fails to start again after cooling down overnight. No prior repairs or parts have been replaced recently. The vehicle is currently non-operational.
Professional Technical Analysis
The 1990 Mazda RX-7 features a 1.3L Wankel rotary engine, known for its unique design and maintenance quirks, with an estimated mileage of 170,000. The vehicle exhibits no starting condition despite confirming the presence of both fuel and spark. Initial diagnostic steps should include a compression test, as the rotary engine relies on apex seals for maintaining combustion chamber pressure. The reported low compression readings suggest a burned apex seal, which can lead to insufficient compression for ignition, thus preventing the engine from starting. Additionally, the recommendation to pull a specific fuse to clear potential flooding indicates a common issue in these engines where excess fuel may accumulate, affecting the starting process. The vehicle’s intermittent starting behavior—able to start when warm but failing when cold—further supports the diagnosis of a seal-related issue. A thorough inspection of the charging system and electrical connections is necessary, as fluctuation in voltage or poor connections can also contribute to starting issues.
Possible Causes
Most common causes (ordered by frequency):
- Burned Apex Seal: The low compression readings indicate a burned apex seal, a common failure in rotary engines, which prevents the necessary compression for ignition. Typically, this leads to two low bounces followed by one high during compression testing. - Compression test results show low readings; intermittent starting behavior when warm; inability to start when cold.
- Flooded Engine Condition: Excess fuel accumulation due to prolonged cranking can flood the engine, making it difficult to start. This is particularly common in rotary engines when injectors remain open too long. - Owner reports difficulty starting after repeated attempts; suggestion to pull fuse to clear flooding.
- Electrical Connection Issues: Poor electrical connections or corroded terminals can lead to intermittent spark delivery or fuel injector operation, contributing to starting difficulties. - Check for corrosion at battery terminals and ignition system connections; irregularities in spark delivery.
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 - Compression Test: Conduct a compression test on the rotary engine to verify apex seal integrity. Expected readings should be consistent across the three compression tests. Any significant deviation, especially low readings, indicates a burned apex seal. Use a compression gauge specifically rated for rotary engines.
- STEP 2 - Electrical System Inspection: Check all electrical connections, particularly at the battery and ignition system. Look for corrosion or loose connections that could affect spark delivery. Use a multimeter to check voltages at the ignition coil and verify that the correct voltage is reaching the spark plugs.
- STEP 3 - Fuel System Check: Inspect the fuel injectors and ensure they are not leaking or remaining open too long, causing flooding. Temporarily disable the injectors by removing the relevant fuse and crank the engine to clear excess fuel.
- STEP 4 - Attempt Starting Procedure: After performing the above checks, reinsert the fuse, turn the ignition on without starting, and check for any abnormal fuel odors indicating flooding. Then attempt to start the engine while monitoring for any unusual noises or behavior.
