Fuel System Issues:
* Fuel Pump (as you suspected): A weak fuel pump might deliver insufficient fuel under load (acceleration or uphill driving), causing chugging. It might still be able to supply enough for idling, but then falter. A fuel pressure test is crucial here.
* Fuel Filter: A clogged fuel filter restricts fuel flow, leading to similar symptoms. This is a relatively inexpensive part to replace and should be done routinely.
* Fuel Injectors: Clogged or faulty fuel injectors can cause inconsistent fuel delivery, resulting in a rough running engine and stalling. Testing involves checking fuel injector pressure and spray pattern.
* Mass Airflow Sensor (MAF): This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can provide incorrect information to the computer, leading to a lean or rich fuel mixture and poor performance.
Ignition System Issues:
* Worn Distributor Cap and Rotor (if applicable): While less common in 1994, some LeSabres still used distributors. Cracks or worn contacts can interrupt the spark, causing misfires and poor running.
* Ignition Coil: A weak or failing ignition coil can provide insufficient spark to one or more cylinders.
* Worn Ignition Wires: Cracked or damaged ignition wires can also cause misfires.
Other Possibilities:
* EGR Valve (as you suspected): A stuck-open EGR valve can lead to poor engine performance, but it's less likely to cause complete stalling.
* PCV Valve: A clogged Positive Crankcase Ventilation valve can cause excessive crankcase pressure, affecting engine performance.
* Intake Air Leaks: A vacuum leak in the intake system can cause a lean fuel mixture, resulting in poor performance.
* Oxygen Sensor: This sensor monitors exhaust gases and helps control the air/fuel mixture. A faulty sensor can cause a rich or lean condition.
* Throttle Position Sensor (TPS): A malfunctioning TPS can send incorrect information to the engine control unit (ECU), leading to poor drivability.
Troubleshooting Steps:
1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to retrieve any stored trouble codes from the car's computer. This will give you valuable clues about the problem.
2. Fuel Pressure Test: This is crucial to rule out fuel delivery problems.
3. Visual Inspection: Carefully inspect the fuel filter, vacuum lines, ignition wires, distributor cap (if equipped), and other components for obvious signs of damage or wear.
4. Listen for Unusual Noises: Pay attention to any unusual noises from the engine, such as knocking or ticking, which can indicate other problems.
Recommendation:
Start with the simplest and cheapest checks – the fuel filter, a visual inspection, and retrieving DTCs. If those don't reveal the issue, then move onto more involved tests like fuel pressure and MAF sensor checks. Consider seeking professional help from a qualified mechanic if you're not comfortable performing these checks yourself, especially the fuel pressure test. A systematic approach based on the diagnostic trouble codes and testing will pinpoint the cause much faster than random part replacement.
