1. Check the Basics First:
* Listen for the fuel pump: Have someone turn the ignition key to the "ON" position (don't crank the engine). You should hear a brief humming sound from the fuel pump in the tank. This sound usually only lasts a couple of seconds. If you don't hear it, the pump might be faulty, the relay is bad, or there's a wiring issue.
* Check the fuel pressure: This is the most definitive test. You'll need a fuel pressure gauge that's compatible with your car's fuel system. Consult your repair manual for the correct specification and where to connect the gauge. The pressure should be within the manufacturer's specifications. Low pressure indicates a problem in the fuel delivery system, potentially the pump. A fuel pressure tester is relatively inexpensive to buy or rent.
* Examine the fuel filter: A clogged fuel filter will restrict fuel flow, mimicking a weak pump. It's relatively easy and inexpensive to replace. If it's severely clogged, that could be the entire problem.
* Check the fuel lines: Inspect the fuel lines visually for cracks, leaks, or kinks. Any damage will restrict fuel flow.
2. More Advanced Diagnosis (If the basics check out):
* Fuel pump relay: If you didn't hear the pump prime when the key was turned to "ON," check the fuel pump relay. Your owner's manual or an online repair manual should show you the location and how to test it. A multimeter can be used to verify if it's receiving power and switching correctly.
* Wiring harness: Inspect the wiring harness leading to the fuel pump for any damage, corrosion, or broken wires.
3. Things that mimic fuel pump failure:
* Clogged Catalytic Converter: A severely clogged catalytic converter can restrict exhaust flow, causing the engine to starve for air and act like it's fuel-starved.
* Ignition System Problems: Weak spark, faulty ignition coil, or other ignition problems can prevent the engine from starting or running smoothly.
* Mass Airflow Sensor (MAF) Sensor: A faulty MAF sensor provides inaccurate readings to the engine's computer, leading to poor fuel mixture and poor performance.
* Fuel Injectors: Clogged or faulty injectors will not deliver the proper amount of fuel.
Important Considerations:
* Safety First: Gasoline is highly flammable. Work in a well-ventilated area, away from open flames or sparks. Disconnect the battery negative terminal before working on the fuel system.
* Repair Manual: A repair manual specific to your 1996 Cadillac DeVille is invaluable. It will provide detailed diagrams, specifications, and troubleshooting procedures.
* Professional Help: If you're not comfortable performing these tests or repairs yourself, take your car to a qualified mechanic. Incorrect diagnosis can lead to unnecessary repairs and expense.
By systematically checking these items, you'll significantly narrow down the possibilities and determine with more certainty if the fuel pump is indeed the culprit. Remember, replacing the fuel pump can be labor-intensive, so accurate diagnosis is crucial.
