1. Crankshaft Position Sensor (CKP Sensor): This is a HIGHLY likely culprit. Even if your pickup coil (which is often part of the distributor) tests okay, the CKP sensor is a separate component that tells the ECU the position of the crankshaft. A faulty CKP sensor prevents the ECU from sending the signal to fire the coil. It's relatively inexpensive to replace. Test it with a multimeter, following the instructions in your repair manual.
2. Cam Position Sensor (CMP Sensor): Some 1991 Sunbirds may have a CMP sensor. This sensor works in conjunction with the CKP sensor to precisely time the ignition. A faulty CMP sensor can prevent a spark. Again, check your repair manual for testing procedures.
3. ECU (Engine Control Unit): The ECU is the "brain" of your engine. If it's faulty, it won't send the necessary signals to create a spark, even if all other components are good. This is the least likely scenario if the previous components checked out, but if everything else fails, it's something to consider. ECU testing is usually best left to a professional unless you have specialized equipment.
4. Wiring and Connections: Carefully inspect all wiring harnesses and connectors related to the ignition system, looking for damaged, corroded, or loose connections. Pay particular attention to the connections between the sensors, the ECU, the ignition module, and the coil. A broken wire can cause an intermittent or complete failure.
5. Ignition Switch: While less likely, a faulty ignition switch can prevent power from reaching the ignition system. Check the switch for proper operation and continuity.
6. Fuel Pressure Regulator: While you mentioned hearing the fuel pump, ensure you have adequate fuel pressure at the rail. A faulty fuel pressure regulator could be allowing fuel to return to the tank, preventing sufficient fuel delivery for ignition even if the pump works.
Troubleshooting Steps:
1. Get a Repair Manual: A factory service manual for your specific 1991 Sunbird 2.0L is essential. It will have detailed wiring diagrams, component locations, and testing procedures.
2. Systemic Approach: Don't just randomly replace parts. Follow a logical troubleshooting path, starting with the most likely culprits (CKP/CMP sensors) and working your way down the list.
3. Visual Inspection: Carefully inspect all components for visible damage, corrosion, or loose connections.
4. Multimeter Testing: Use a multimeter to test the voltage and continuity of all components and wiring according to your repair manual's instructions.
If you're not comfortable working on your car's electrical system, it's best to take it to a qualified mechanic. Attempting repairs without the proper knowledge and tools could potentially cause further damage.
