Fuel System:
* Fuel Pump: Check if the fuel pump is operating. You can listen for the pump's whine when the ignition is turned on (often best heard near the fuel tank). A pressure gauge test at the fuel rail is definitive – it should read within the manufacturer's specifications. A weak pump could explain cranking but no start.
* Fuel Injectors: Check for fuel injector pulse. A noid light or oscilloscope can be used to confirm that the injectors are receiving the signal to open and spray fuel. A clogged injector or a faulty injector is a possibility.
* Fuel Filter: A clogged fuel filter restricts fuel flow, preventing the engine from getting enough fuel to start. This is a relatively inexpensive and easy check.
* Fuel Pressure Regulator: This regulator maintains fuel pressure in the fuel rail. A faulty regulator can cause low fuel pressure or even leaks.
Air System:
* Air Filter: A severely clogged air filter can restrict airflow enough to prevent starting. This is a quick and easy check.
* Mass Airflow Sensor (MAF) Sensor: A faulty MAF sensor provides inaccurate readings to the ECM, leading to incorrect fuel delivery and a no-start condition. Cleaning the sensor (if possible) or replacing it might solve the problem.
Other Potential Issues:
* Crankshaft Position Sensor (CKP): This sensor tells the ECM where the crankshaft is positioned. A faulty CKP sensor prevents the ECM from knowing when to fire the injectors.
* Cam Position Sensor (CMP): Similar to the CKP sensor, this one tells the ECM the position of the camshaft. A faulty CMP prevents proper timing of the fuel injection and ignition.
* Ignition Coil: Though you mentioned ignition system checks, verify that the coil is producing sufficient spark to all cylinders. A weak coil can lead to a no-start condition, especially in cold weather.
* Wiring and Connections: Double-check all wiring harnesses, connectors, and grounds for corrosion, breaks, or loose connections. A poor connection can disrupt the signal path in the critical components mentioned above.
* Immobilizer System (if equipped): Some vehicles have an immobilizer system that prevents the engine from starting unless the correct key is used. Check if this system is interfering.
Troubleshooting Methodology:
1. Start with the simplest and cheapest checks: Fuel filter, air filter, and listening for the fuel pump.
2. Use a systematic approach: Don't jump around. Follow the flow of fuel and spark, checking each component systematically.
3. Use diagnostic tools: An OBD-II scanner (for 1996 and later cars, but perhaps a generic code reader might show something) can provide valuable information about engine trouble codes. More advanced scanners can monitor sensor readings in real-time.
Replacing the ECM is a significant step, so it's crucial to eliminate other, more common, causes first. Remember to always consult a repair manual specific to your 1993 Mitsubishi Diamante wagon for detailed diagnostic procedures and specifications.
