Ignition System:
* Spark Plug: The most common culprit. It could be fouled (covered in oil, fuel, or carbon), damaged (cracked insulator, worn electrode), or loose.
* Spark Plug Wire: A cracked, frayed, or loose wire prevents the spark from reaching the plug. Check for proper connection and insulation integrity. Look for arcing.
* Ignition Coil: If the Cavalier has individual coil packs (one per cylinder), a faulty coil for cylinder 4 will prevent sparking. If it has a single coil with distributor, the distributor cap and rotor may be cracked or worn at the number 4 terminal.
* Ignition Control Module (ICM): This module controls the firing sequence. A faulty ICM can cause misfires in one or more cylinders.
* Crankshaft Position Sensor (CKP): This sensor tells the computer the engine's rotational position, crucial for timing the spark. A failing CKP will lead to misfires or no spark at all.
Fuel System:
* Fuel Injector: A clogged or faulty injector for cylinder 4 won't deliver fuel, preventing combustion.
* Fuel Pressure: Insufficient fuel pressure throughout the system can affect all cylinders, but a partially clogged fuel filter could affect one cylinder more than others.
* Fuel Pump: A weak fuel pump can't provide enough pressure, although this usually affects multiple cylinders.
Engine Mechanical Issues:
* Valve Problem: A burnt, bent, or sticking valve in cylinder 4 will prevent proper combustion. This is less common unless there's been significant engine damage.
* Compression: Low compression in cylinder 4 indicates a leak in the piston rings, cylinder head gasket, or valves. A compression test is needed to diagnose this.
Other Possibilities:
* Vacuum Leaks: A significant vacuum leak can affect engine performance, potentially causing a misfire.
* Computer/ECM Problems: The Engine Control Module (ECM) could have a fault affecting cylinder 4 specifically. A diagnostic scan code reader is necessary here.
Troubleshooting Steps:
1. Start with the simplest: Check the spark plug and wire for cylinder 4 first. Visually inspect them for damage and securely reconnect them.
2. Visual Inspection: Look for any obvious signs of damage or leaks around cylinder 4.
3. Diagnostic Scan: Use an OBD-II scanner (if equipped) to retrieve any diagnostic trouble codes (DTCs). This can pinpoint the problem area. A 1992 model might require a specialized scanner.
4. Compression Test: If other checks don't reveal the problem, a compression test will reveal if there's a mechanical issue in cylinder 4.
5. Fuel Injector Test: A fuel pressure test and injector flow test can determine if the injector is functioning properly.
Important Note: Without a proper diagnostic scan and potentially some testing equipment (like a multimeter and compression gauge), pinpointing the exact cause can be challenging. It's best to consult a qualified mechanic for accurate diagnosis and repair, especially if you lack experience working on cars.
