* Distributor Cap and Rotor: These are wear items and can crack, causing poor or no spark. Inspect them carefully for any damage or carbon tracking. Even a tiny crack can disrupt the spark.
* Ignition Wires (Spark Plug Wires): These can become brittle, cracked, or corroded, leading to poor spark delivery or no spark at all. Check each wire for damage and ensure they're securely connected at both ends. A simple visual inspection isn't enough; you might need a wire tester to ensure continuity.
* Spark Plugs: Worn, fouled, or damaged spark plugs prevent proper ignition. Replace them with new, correctly gapped plugs.
* Wiring Harness Issues: A break or short in the wiring harness between any of the components you've already replaced (or between them and the spark plugs) could interrupt the circuit. This often requires a careful visual inspection of the entire harness, looking for any frayed, broken, or corroded wires.
* Crank Position Sensor Wiring: Even with a new sensor, if the wiring to it is faulty, it won't work correctly. Check the wiring carefully for damage.
* Ignition Switch: A faulty ignition switch might not be sending power to the ignition system.
* Power Supply Issues: Ensure the ignition system is receiving adequate power from the battery and related circuits. Check fuses and relays related to the ignition system.
* ECM (Engine Control Module) / ECU (Engine Control Unit): Though less likely after replacing the ignition module, a faulty ECM could prevent spark generation. This is harder to diagnose and may require specialized tools.
* Incorrect Installation: Double-check that you installed all the new parts correctly. Even a slightly misaligned distributor cap or incorrectly connected wire can prevent spark. Refer to a service manual for the correct procedures.
Troubleshooting Steps:
1. Visual Inspection: Start with a thorough visual inspection of all components mentioned above.
2. Basic Electrical Tests: Use a multimeter to check for power and ground at various points in the ignition system. A service manual will provide diagrams showing where to check.
3. Spark Tester: Use an inline spark tester to verify if spark is reaching the distributor cap. This helps isolate whether the problem is before or after the distributor.
4. Professional Diagnosis: If you're not comfortable performing electrical tests, take your truck to a qualified mechanic. They have specialized tools and knowledge to pinpoint the problem quickly and efficiently.
Remember to consult a Nissan D21 repair manual specific to your engine for wiring diagrams and component locations. This will significantly aid your troubleshooting process. Working on ignition systems can be dangerous; take necessary precautions and disconnect the battery negative terminal before working on any electrical components.
