Here's a breakdown of likely culprits:
* Ignition Switch: This is the most probable suspect. The ignition switch provides power to the coil *only* when the key is in the "run" or "start" position. A faulty switch might not be sending power to the coil even though the rest of the ignition system seems okay.
* Ignition Coil Wiring: Check all the wiring going to and from the ignition coil for breaks, shorts, corrosion, or loose connections. A break in the wire leading to the coil from the ignition switch would explain why you need to bypass it.
* Ignition Control Module (ICM): Some Geo Metros have a separate ICM (sometimes integrated into the distributor). The ICM is essentially an intermediary between the ECU and the coil. A faulty ICM can prevent the coil from receiving the signal to fire. This is less likely if you've already replaced the ECU, but still possible.
* Crankshaft Position Sensor (CKP Sensor): The CKP sensor tells the ECU the engine's rotational position. Without a functioning CKP sensor, the ECU might not send the signal to fire the coil, even if everything else is working correctly.
* Cam Position Sensor (CMP Sensor): Similar to the CKP sensor, a faulty CMP sensor can prevent proper ignition timing and firing.
Troubleshooting Steps:
1. Check the Ignition Switch: This is the easiest and most likely place to start. You may need a wiring diagram to trace the power wire from the ignition switch to the coil.
2. Inspect Wiring: Carefully examine all wiring related to the ignition system, paying close attention to connections at the coil, ignition switch, and any related components (ICM, distributor). Look for anything that looks damaged, corroded, or loose.
3. Test the Ignition Coil: You can test the coil's primary and secondary windings using a multimeter to rule out a faulty coil itself.
4. Check for Power at the Coil: With the key turned to the "run" position, use a multimeter to check if there's power reaching the coil's positive terminal. If there isn't, the problem is upstream (ignition switch, wiring, ICM).
5. Check CKP and CMP Sensors (if applicable): These sensors are crucial for proper ignition timing. A malfunctioning sensor could lead to the symptoms you're describing. Testing these typically requires a multimeter and possibly a scan tool.
Important Note: Working with automotive electrical systems can be dangerous. If you are not comfortable working with electricity and automotive systems, it's best to take your vehicle to a qualified mechanic. Improperly diagnosing or repairing electrical problems can lead to further damage or injury. Use caution and follow proper safety procedures.
