1. Observe Symptoms: A bad fuel pressure regulator often manifests in these ways:
* Rough idle or stalling: Particularly noticeable when the engine is warm. This is because the faulty regulator might allow fuel to leak back into the intake manifold, creating a lean condition.
* Poor fuel economy: Leaking fuel means wasted fuel.
* Hard starting: Related to the lean condition caused by fuel leaking back.
* Hesitation or stumbling under acceleration: Again, a lean condition from fuel leakage will cause this.
* Smell of fuel: A strong gasoline odor might be present, especially around the intake manifold. This is a significant indicator but not definitive proof.
* Fuel pressure test: This is the most conclusive test
2. Fuel Pressure Test (Crucial): This is the only way to know for sure. You'll need a fuel pressure gauge specifically designed for automotive use and the correct fitting to connect to your fuel system. Warning: Gasoline is highly flammable, so exercise extreme caution. Disconnect the negative battery terminal before working with the fuel system.
* Locate the fuel pressure test port: Consult your Cadillac Seville STS repair manual for the exact location. It's usually on the fuel rail.
* Connect the gauge: Carefully connect the gauge to the test port.
* Start the engine: Observe the fuel pressure reading. The pressure should be within the specifications listed in your repair manual (typically between 30-45 psi for this engine, but check your manual for the exact numbers). Let the engine idle for several minutes and watch for pressure fluctuations.
* Turn off the engine: After turning off the engine, monitor the pressure. If the pressure drops slowly (over several minutes), it suggests a leaking fuel pressure regulator. If the pressure drops immediately, the problem is elsewhere (e.g., leaking injector o-rings, faulty fuel pump).
3. Vacuum Test (Optional, but helpful): A faulty regulator can sometimes cause a vacuum leak. A vacuum gauge can help detect this.
4. Visual Inspection (Least Reliable): Inspect the fuel pressure regulator itself for any obvious signs of damage, leaks, or corrosion. This is not very reliable as many failures are internal and not visible.
Important Considerations:
* Repair Manual: A factory repair manual for your 1993 Cadillac Seville STS is invaluable. It will provide precise fuel pressure specifications, test procedures, and component locations.
* Professional Help: If you're not comfortable working on your fuel system, it's best to take your car to a qualified mechanic for diagnosis and repair. Incorrect fuel system repair can be dangerous.
* Other Potential Problems: Symptoms like those listed above could also be caused by a faulty fuel pump, clogged fuel filter, malfunctioning mass airflow sensor, or other issues. A thorough diagnostic process is essential.
The fuel pressure test is the key. If the test reveals a problem, it strongly suggests a failing fuel pressure regulator. However, always consider other potential causes before replacing parts.
