Ignition System (beyond cap, rotor, wires, plugs):
* Distributor Rotor: While you replaced the cap, did you inspect the rotor? A worn or cracked rotor can cause misfires.
* Ignition Coil: A failing ignition coil can't supply sufficient voltage to all cylinders consistently. This is a common culprit for intermittent misfires. The 4.3L Vortec uses an individual coil per cylinder, so a single faulty coil will cause a misfire in just one cylinder.
* Ignition Control Module (ICM): This module controls the ignition system. A faulty ICM can lead to misfires, especially under load or at higher RPMs.
* Pick-up Coil (in the distributor): This sensor senses the position of the rotor and sends signals to the ICM. A faulty pick-up coil will disrupt the ignition timing.
Fuel System:
* Fuel Injectors: A clogged or failing fuel injector can deprive a cylinder of fuel, causing a misfire. This is more likely to cause a consistent misfire in one cylinder.
* Fuel Pressure Regulator: A malfunctioning fuel pressure regulator can deliver inconsistent fuel pressure, leading to misfires.
* Fuel Pump: A weak fuel pump may not deliver enough fuel under higher engine loads.
Other Potential Causes:
* Vacuum Leaks: A vacuum leak can disrupt the engine's air/fuel mixture, leading to misfires.
* Camshaft Position Sensor (CMP Sensor): This sensor is crucial for proper ignition timing. A faulty sensor can result in misfires.
* Crankshaft Position Sensor (CKP Sensor): Similar to the CMP sensor, a faulty CKP sensor can disrupt ignition timing.
* PCV Valve: A blocked Positive Crankcase Ventilation (PCV) valve can build up pressure in the crankcase and lead to misfires.
Troubleshooting Steps:
1. Check for error codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored in the engine's computer. This is the single most important step. The code will often pinpoint the problem.
2. Visual Inspection: Carefully examine all ignition components for damage or wear.
3. Compression Test: A compression test will check the compression in each cylinder. Low compression in one or more cylinders indicates a mechanical problem like worn rings, valves, or head gasket issues.
4. Fuel Pressure Test: Measure the fuel pressure to ensure it's within specifications.
5. Vacuum Test: Check for vacuum leaks using a vacuum gauge or by spraying carb cleaner around potential leak points and listening for a change in engine RPM.
Without knowing specific symptoms (e.g., which cylinder is misfiring, if the misfire is constant or intermittent, engine roughness, etc.), it's impossible to give a definitive answer. Start with the OBD-II scanner – it will be your best guide. If you're not comfortable performing these tests yourself, take your Blazer to a qualified mechanic for diagnosis and repair.
