I. Safety First:
* Disconnect the negative battery terminal before performing any electrical tests.
II. Basic Checks:
1. Fuel Pump Relay: This is a common culprit. Locate the fuel pump relay (usually in the underhood fuse box, consult your owner's manual for exact location). Swap it with a known good relay of the same amperage (or test it with a multimeter if you have one). If the problem goes away, you've found your culprit.
2. Fuel Pump Inertia Switch: Some cars have an inertia switch to cut power to the fuel pump in a collision. Locate this (often under the dash or in the trunk) and press the button to reset it.
3. Check for obvious fuel leaks: Inspect the fuel lines, filter, and fuel tank for any leaks.
III. More Advanced Diagnostics:
1. Listen for the fuel pump: Have someone crank the engine while you listen near the fuel tank. You should hear a brief whirring sound as the pump primes. If you don't hear it, the pump, relay, or wiring is likely the problem.
2. Check fuel pressure: This requires a fuel pressure gauge (available at auto parts stores). Connect it to the fuel rail (usually near the intake manifold) and have someone crank the engine. You should see a pressure build-up to the specified amount (consult your shop manual for the correct specification). Low or no pressure indicates a problem with the fuel pump, filter, pressure regulator, or fuel lines.
3. Inspect the fuel filter: A clogged fuel filter will restrict fuel flow. It's relatively inexpensive and easy to replace.
4. Check the fuel injectors: While less likely to cause a complete no-start, faulty injectors can be a contributor. This usually requires a fuel injector tester or a pressure gauge reading at the injectors themselves. A professional scan tool might reveal injector faults.
5. Check the ignition system: Although you're suspecting fuel, ensure the ignition system is functioning correctly. Check for spark at the spark plugs (use a spark tester or gap a spark plug and hold it close to the engine block). A weak or missing spark can sometimes mimic fuel problems.
6. Check for codes (if equipped): Does your car have an OBD-I system? (This is less likely for a 1989 model, but worth checking) Some codes might relate to fuel system issues. You might need a code reader specifically designed for OBD-I systems.
IV. Possible Causes and Their Implications:
* Fuel Pump: Failed pump, clogged pickup in the tank, or wiring issues.
* Fuel Filter: Clogged filter restricting fuel flow.
* Fuel Relay: Faulty relay preventing the pump from energizing.
* Fuel Pressure Regulator: Malfunctioning regulator allowing pressure to bleed off.
* Fuel Injector(s): Clogged or malfunctioning injectors.
* Inertia Switch: Tripped switch cutting power to the fuel pump.
* Wiring: Damaged or corroded wiring in the fuel pump circuit.
V. When to Seek Professional Help:
If you're not comfortable working on your car's fuel system (it involves working with flammable material), or if you've checked the basic items and still haven't found the issue, take it to a qualified mechanic. They'll have the tools and expertise to diagnose and repair the problem safely and efficiently. A fuel pressure gauge and a diagnostic scanner are key tools they'll use.
Remember to always consult a repair manual specific to your 1989 Cadillac DeVille 4.5L for detailed diagrams, specifications, and procedures. This will make troubleshooting much easier and safer.
