Clear Indications (strong likelihood of a bad fuel pump):
* No start: This is the most obvious sign. The engine cranks but won't start because no fuel is being delivered.
* Intermittent starting: The car starts sometimes, but other times it cranks but won't fire up. This is often due to the pump struggling to deliver enough fuel consistently.
* Engine sputtering/hesitation/stalling, especially under acceleration: The engine may run fine at idle but sputters, hesitates, or stalls when you accelerate, indicating a lack of fuel supply.
* Reduced fuel pressure (requires testing): A mechanic can use a fuel pressure gauge to directly measure fuel pressure. Low pressure is a definitive indicator of a bad fuel pump.
Less Clear Indications (could be other issues):
* Weak acceleration: While weak acceleration *can* be a fuel pump issue, it's also a symptom of many other problems (e.g., clogged fuel filter, failing ignition components, air intake restrictions).
* Loud humming or whining noise from the fuel tank: You might hear a buzzing or whirring sound from the rear of the car when the ignition is turned on (but the engine isn't running). This is a sign the pump is struggling. However, it's not always present even with a failing pump.
* Fuel gauge inaccuracy: While unlikely to be the direct cause, a failing fuel pump could affect the electrical system that feeds the gauge.
Troubleshooting Steps (before replacing the pump):
1. Check the fuel filter: A clogged filter restricts fuel flow and mimics fuel pump symptoms. This is a much cheaper and easier fix.
2. Check the fuel pump relay: A faulty relay can prevent the pump from receiving power. This is also a relatively inexpensive and easy check.
3. Check the fuel pressure: As mentioned above, this is the most definitive test.
Important Note: Replacing a fuel pump in a 1991 Caprice is a relatively involved job, often requiring dropping the fuel tank. It's best left to someone experienced with automotive repair unless you're comfortable with that level of mechanical work. Improper installation can lead to further damage.
