Ignition System:
* Ignition Switch: A faulty ignition switch won't send power to the rest of the system, even if everything else is new. Check if power is reaching the coil when the key is turned.
* Wiring: Damaged or corroded wiring anywhere in the ignition circuit can interrupt the spark. Inspect all wires going to and from the coil, distributor, and ECU. Look for fraying, broken wires, or corrosion.
* Crankshaft Position Sensor (CKP Sensor): This sensor tells the ECU where the engine is in its cycle to provide the correct spark timing. A faulty CKP will prevent starting.
* Camshaft Position Sensor (CMP Sensor): Similar to the CKP sensor, but for the camshaft. Important for fuel injection timing in some systems.
* Ignition Coil (even with a new one): While you replaced it, it's possible the new coil is defective or there's a problem with its connections. Double-check its installation.
* Distributor Cap and Rotor: Even with a new distributor, these parts can be faulty or incorrectly installed. Check for cracks or carbon tracking on the cap and ensure the rotor is correctly seated and spins freely.
* Spark Plugs and Wires: Check the spark plugs for proper gap and condition. Inspect the plug wires for cracks or damage. Test for spark at the plugs using an inline spark tester.
Fuel System:
* Fuel Filter: A clogged fuel filter, even with a new pump, can prevent sufficient fuel flow. Replace it.
* Fuel Injectors: The injectors might be clogged or not getting the proper signal from the ECU. You could try a fuel injector cleaner, but a proper test is needed to confirm their operation.
* Fuel Pressure Regulator: This regulates fuel pressure in the system. A faulty regulator can lead to insufficient fuel pressure.
* Airflow Sensor (AFM): A bad AFM sensor will affect the fuel/air mixture calculation by the ECU resulting in a no-start condition.
Other Possibilities:
* Neutral Safety Switch: In an automatic transmission, this switch prevents starting unless the car is in Park or Neutral. Check its operation.
* Grounds: Poor ground connections can disrupt the entire electrical system. Clean all ground points.
* ECU Programming/Sensor Calibration: If a sensor was replaced, it might need to be calibrated or the ECU may need to be re-programmed (though less likely for a simple swap). This is more likely if you replaced the ECU with a used one.
* Immobilizer (if equipped): Some later model Supras may have an immobilizer system. If the key isn't recognized, the car won't start.
Troubleshooting Steps:
1. Check for Spark: Test for spark at the spark plugs. This is crucial to eliminate ignition problems.
2. Check for Fuel Pressure: Measure fuel pressure at the fuel rail. This will tell you if fuel is getting to the injectors.
3. Check for Fuel Injector Pulse: Use a multimeter or a noid light to see if the injectors are being pulsed by the ECU.
4. Inspect Wiring Harnesses: Carefully inspect all wiring harnesses for damage or corrosion, paying special attention to connectors.
5. Check all fuses and relays.
6. Check ground connections.
If you lack experience with automotive diagnostics, it's best to seek help from a qualified mechanic specializing in older vehicles. Trying to diagnose this issue without proper tools and knowledge could lead to further damage. A systematic approach, checking each system one by one, is the most effective way to find the culprit.
