Ignition System:
* Crankshaft Position Sensor (CKP): This is a very common cause of sudden rough running or no-start. The CKP tells the computer where the engine is in its rotation cycle. A failing sensor gives the computer bad information, leading to misfires and rough running.
* Camshaft Position Sensor (CMP): Similar to the CKP, a faulty CMP sensor will cause the computer to misinterpret engine timing and lead to rough running.
* Ignition Coil(s): A failing ignition coil can cause misfires on one or more cylinders, resulting in a rough idle and running. This is more likely if the roughness is accompanied by a noticeable misfire sound.
* Ignition Module: This part controls the ignition coils. A faulty module can cause multiple misfires.
* Worn Distributor Cap and Rotor (if applicable): While less common in later Vortec models, some might still have a distributor. Carbon buildup or wear can cause poor spark delivery.
* Spark Plugs and Wires: Though less likely to cause a *sudden* problem, worn plugs or wires could be the root if they were already nearing the end of their lifespan.
Fuel System:
* Fuel Pump: A failing fuel pump might not be delivering enough fuel pressure. This would lead to rough running, especially under load. Listen for the fuel pump whirring when you turn the key to the "on" position (before cranking).
* Fuel Filter: A clogged fuel filter can restrict fuel flow, causing similar problems to a failing fuel pump.
* Mass Airflow Sensor (MAF): A faulty MAF sensor provides inaccurate readings to the computer about the amount of air entering the engine, leading to a rich or lean condition and rough running.
* Throttle Position Sensor (TPS): A faulty TPS can give inaccurate throttle position information, disrupting the air/fuel mixture.
Other Possibilities:
* Vacuum Leaks: A significant vacuum leak can disrupt engine performance and cause rough running.
* Low Compression in One or More Cylinders: While less likely to appear suddenly, a failing head gasket or valve issue could cause this. A compression test would help diagnose this.
* Engine Coolant Temperature (ECT) Sensor: An inaccurate reading from the ECT sensor can lead to poor fuel mixture control.
Troubleshooting Steps:
1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to check for any stored codes. This is the quickest way to narrow down the possibilities.
2. Listen for Misfires: A distinct "popping" or "chugging" sound usually indicates misfires. This helps pinpoint the ignition system.
3. Inspect Spark Plugs and Wires: Check the condition of your spark plugs – are they worn, fouled, or damaged? Inspect the wires for cracks or damage.
4. Check Fuel Pressure: A fuel pressure gauge is necessary to check if the fuel pump is delivering adequate pressure.
5. Inspect Vacuum Hoses: Check all vacuum hoses for cracks or leaks.
It's best to start with the easiest and most common culprits (CKP sensor, ignition coils, MAF sensor) before moving on to more involved diagnostics. If you lack the experience to diagnose these issues yourself, take it to a qualified mechanic for proper diagnosis and repair.
