1. Verify Ignition Switch:
* Check the ignition switch: Ensure it's functioning correctly. A faulty switch won't send power to the rest of the system. You can test this with a multimeter by checking for power at the switch in the "start" position and tracing it to the next component in the circuit.
2. Check for Power and Ground:
* Power to the ignition module: The ignition module needs power to operate. Use a multimeter to check for battery voltage at the module's power supply terminals with the ignition key turned to the "on" position.
* Ground connection: A poor ground connection can prevent the system from working. Inspect the ground wire connecting the ignition module to the engine block for corrosion or looseness. Clean the connection and ensure a good ground.
3. Inspect the Crankshaft Position Sensor (CKP Sensor):
* The CKP sensor tells the ignition module when to fire the spark. A faulty sensor will prevent sparking. You'll need to locate the sensor (usually near the crankshaft pulley) and check it's connection, visually inspect it for damage, and possibly test its output with a multimeter or oscilloscope (more advanced testing). A failing CKP sensor often gives a no-start condition.
4. Examine the Pickup Coil (in distributor if equipped, some models used a CKP instead):
* If your engine uses a distributor (less common on later 2.3L engines), the pickup coil within the distributor provides the signal to the ignition module. Check for cracks or damage to the coil, and the connection to the module.
5. Check the Wiring:
* Visually inspect all wiring: Look for any broken, frayed, or corroded wires between the ignition switch, the ignition module, the coil packs, the crankshaft position sensor, and the distributor (if equipped). Pay close attention to the connectors at each component.
* Continuity test: Use a multimeter to check the continuity (electrical connection) of all wires in the ignition circuit.
6. Consider the PCM (Powertrain Control Module):
* Although less likely, a faulty PCM (computer) could be preventing the ignition system from functioning correctly. This is usually a more advanced diagnostic step requiring specialized equipment.
7. Test the Spark Plugs and Wires:
* Even though you've replaced the coils, ensure the spark plugs and wires are in good condition. Inspect them for damage and, ideally, test them individually.
Important Notes:
* Safety First: Disconnect the negative battery terminal before working on any electrical components.
* Wiring Diagram: A wiring diagram for your specific 1991 Ford Ranger 2.3L engine is essential for proper troubleshooting. You can find one online through various automotive repair resources or a Haynes/Chilton manual.
* Professional Assistance: If you are not comfortable working with automotive electrical systems, it's best to take your vehicle to a qualified mechanic for diagnosis and repair.
By systematically checking these components, you should be able to pinpoint the source of the no-spark issue. Remember to always refer to a wiring diagram to accurately trace the circuits.
