Fuel System:
* Fuel Pressure: Insufficient fuel pressure is a common culprit. Use a fuel pressure gauge to check if the pressure is within specifications for your engine. A low reading might indicate a faulty fuel pump, clogged fuel filter, or a problem with the fuel pressure regulator.
* Fuel Injectors: A clogged or malfunctioning fuel injector can prevent sufficient fuel from reaching the combustion chamber. Testing the injectors (either with a noid light or by performing a pressure test) is crucial.
* Fuel Delivery: Verify that fuel is reaching the engine. Check for leaks in the fuel lines and proper connections.
Ignition System:
* Spark: Weak or no spark will prevent combustion. Check the spark plugs, spark plug wires, ignition coil(s), and ignition control module (ICM) for proper function. A spark tester is essential here. Also, ensure the distributor cap and rotor (if applicable) are in good condition.
* Crankshaft Position Sensor (CKP): This sensor is critical for the engine to know where the pistons are. A faulty CKP sensor can cause starting issues and running problems.
* Cam Position Sensor (CMP): Similar to the CKP, a faulty CMP prevents proper timing synchronization.
Air System:
* Vacuum Leaks: A significant vacuum leak can disrupt the air-fuel mixture, making the engine difficult to keep running. Inspect all vacuum hoses and connections carefully.
* Mass Airflow Sensor (MAF): A dirty or faulty MAF sensor can provide incorrect air readings, leading to a poor air-fuel mixture. Try cleaning it or replacing it if necessary.
* Throttle Position Sensor (TPS): Incorrect readings from the TPS can prevent proper fueling and ignition timing.
Other Potential Issues:
* Cooling System: Though you've replaced the head gaskets, ensure the cooling system is properly bled of air. Air pockets can prevent proper cooling and potentially cause overheating, leading to intermittent running issues.
* Engine Sensors: Numerous other sensors can influence engine operation. A scan tool can read diagnostic trouble codes (DTCs) that might point to a specific faulty sensor.
* Improper Reassembly: Double-check all connections and components during reassembly. A simple loose wire or improperly seated sensor can cause significant problems.
Troubleshooting Steps:
1. Check for DTCs: Use a scan tool to retrieve any diagnostic trouble codes. This will give you a starting point for diagnosis.
2. Fuel Pressure Test: Measure fuel pressure to ensure it's within the specified range.
3. Spark Test: Check for spark at each spark plug.
4. Vacuum Leak Check: Inspect all vacuum lines and connections for leaks.
5. Check the CKP and CMP sensors.
6. Bleed the cooling system: Ensure there are no air pockets trapped in the coolant system.
Without a scan tool reading codes, the process becomes more of a methodical elimination of possibilities. Start with the easiest checks (visual inspection of vacuum lines, fuel lines, etc.) and work your way to the more complex tests (fuel pressure, sensor checks). If you lack experience working on engines, it is best to take it to a mechanic for diagnosis and repair.
