The EXACT 1991 Corvette Fuel Pump Relay Location (Find It Fast + Fixes!)

Finding the fuel pump relay on a 1991 Chevrolet Corvette is straightforward: It's located in the underhood electrical center, specifically within the auxiliary relay block mounted on the passenger side, front corner of the engine compartment (near the coolant reservoir). Look for a small, typically black, cube-shaped relay.

If your 1991 Corvette C4 cranks but refuses to start, you might instantly suspect a dead fuel pump or a bad fuel pump relay. While the fuel pump itself is a common culprit, the relay controlling its power is frequently overlooked and much simpler to check or replace. Knowing its exact location is the first critical step in diagnosing or solving a no-fuel situation. Located within the engine bay's electrical center, the fuel pump relay plays a vital role in engine operation. When you turn the ignition key to the "Run" position, the Powertrain Control Module (PCM) activates this relay. This completes the circuit, sending a robust 12-volt power supply directly from the battery, through the relay, to the electric fuel pump mounted inside the fuel tank. Without this relay functioning correctly, the pump gets no power, and the engine starves for fuel.

Pinpointing the 1991 Corvette Fuel Pump Relay: Step-by-Step

  1. Locate the Main Underhood Electrical Center: Open your Corvette's hood. Look at the passenger side (right side) of the engine compartment, near the very front corner closest to the headlight.
  2. Identify the Auxiliary Relay Block: You'll see a large, rectangular, black plastic box. This is the main electrical center. However, the fuel pump relay isn't housed inside this primary box itself. Instead, locate the smaller auxiliary relay block mounted directly onto the top or side of this large box. It's a distinct, smaller black plastic housing specifically designed to hold several relays. This smaller block is the key spot.
  3. Find the Fuel Pump Relay within the Block: The auxiliary relay block typically contains multiple identical-looking relays. On the 1991 Corvette, the fuel pump relay is situated in the front right corner of this auxiliary block (when standing in front of the car, looking towards the passenger side). It is often the relay closest to the front bumper and passenger-side headlight assembly within that block.
  4. Confirm the Relay: The auxiliary block usually has labels molded into its plastic cover, indicating the function of each relay position. Look for "FUEL PUMP" or "FP" printed near the specific socket. If the label is missing or worn, the position described (front right corner of the auxiliary block) is definitive for the 1991 model year. The relay itself is a standard automotive cube relay, roughly 1 inch square, with 4 or 5 blade terminals on the bottom. It might be black or dark gray.

(Recommended Image: High-resolution photo taken from above the passenger side front corner of the 1991 Corvette engine bay. Clearly show the large primary electrical center box. Highlight the smaller auxiliary relay block mounted directly on top or on its side. Use a clear arrow or circle pointing precisely to the fuel pump relay in the front right corner of this auxiliary block. Another helpful image would be a close-up of the auxiliary relay block's socket with the label "FUEL PUMP" or "FP" visible.)

How to Remove the 1991 Fuel Pump Relay (Safely)

Diagnosing or replacing the relay requires removal, but safety comes first:

  1. Disconnect the Battery: ALWAYS disconnect the negative (-) battery cable before working on any electrical components. This prevents accidental shorts, sparks, or electrical shocks. Secure the cable away from the battery terminal.
  2. Access the Relay: Locate the auxiliary relay block and the specific fuel pump relay position as described above. You usually don't need to remove any covers over the main electrical center to access the auxiliary block's relays.
  3. Gently Pull the Relay Straight Up: Relays plug directly into their sockets. Firmly grasp the relay body and pull it straight upwards. Avoid excessive wiggling or pulling at an angle, as this can damage the socket terminals or the relay itself. It should release with moderate, even pressure. If stuck, carefully use a small flat-head screwdriver under the relay body to gently pry upwards while pulling.

Symptoms of a Faulty Fuel Pump Relay

Suspect the fuel pump relay if you experience:

  • Engine Cranks But Won't Start: The most obvious sign. The engine turns over normally but doesn't fire due to lack of fuel delivery.
  • Intermittent Starting Issues: The car starts perfectly sometimes, but fails to start on other occasions without an obvious pattern. The relay contacts can become worn or burned, causing intermittent failures when vibration or temperature changes affect them.
  • Engine Stalls Suddenly While Driving: Similar to intermittent starting, a failing relay can abruptly cut power to the fuel pump during operation, causing the engine to die. It might restart after cooling down briefly.
  • No Fuel Pump Prime Sound: When you first turn the ignition key to "Run" (before cranking), you should hear a distinct humming or whining sound from the rear of the car (fuel tank area) for about 2 seconds as the pump primes the fuel lines. No prime sound is a strong indicator of a fuel delivery problem involving the relay, fuse, pump, or wiring.

Testing the 1991 Corvette Fuel Pump Relay

Don't just guess; test it:

  1. Swap Method: This is often the quickest test. Find another relay in the auxiliary block with the same part number (often labeled on the relay side). Relays for functions like the horn, cooling fan(s), or A/C compressor are frequently identical to the fuel pump relay. Swap the suspected fuel pump relay with one of these known-good relays. Example: Swap the horn relay into the fuel pump relay socket. Turn the ignition to "Run" and listen for the fuel pump prime. If the pump now primes, the original fuel pump relay is bad. Remember to swap them back afterward. If the horn stops working after the swap, you know you moved a good relay.
  2. Listen for the Relay "Click":
    • Have an assistant turn the ignition key to the "Run" position.
    • Place your finger firmly on the fuel pump relay body.
    • You should feel and often hear a distinct "click" inside the relay within a second or two of the key being turned to "Run." This "click" indicates the relay coil is activating the electromagnet that pulls the internal switch closed.
    • No Click: If you get no click, the problem could be the relay coil itself, the PCM signal not reaching the relay (wiring issue), or a problem within the PCM controlling circuit. Power supply or ground issues to the relay socket could also cause this.
    • Click But No Pump: If you feel/hear a click, but the pump still doesn't run, the relay's internal contacts could be burned or corroded and unable to pass sufficient current. Move to voltage testing.
  3. Multimeter Voltage Test: Requires a basic digital multimeter (DMM). Test with the relay plugged in. Turn the ignition key to "Run." Carefully back-probe the wires at the connector socket leading to the relay terminals. Find the relay terminal layout diagram (often printed on the relay side or in the service manual). You need to identify:
    • Power Input (Terminal 30 / 87a): Constant Battery Voltage (+12V). Should always read battery voltage (around 12.6V) regardless of ignition position.
    • Control Signal (Terminal 85/86): When ignition is in "Run," one terminal should show battery voltage (from PCM/fuse), and the other should provide a ground path (from PCM). Often around 12V difference measured across pins 85 and 86 when key is "Run". A test light can also confirm activation across these two terminals.
    • Output to Fuel Pump (Terminal 87): This is the terminal supplying power to the pump. With the ignition in "Run," this pin should show battery voltage if the relay is working correctly. If you get voltage here but the pump doesn't run, the issue lies after the relay (pump, wiring to pump, ground for pump).
  4. Bench Testing the Relay (Out of the Car): If the swap or in-car voltage tests are inconclusive, remove the relay.
    • Look for the terminal numbering molded into the plastic base near each pin.
    • Set your multimeter to measure resistance (Ohms).
    • Check continuity between Terminals 30 and 87. Normally, there should be no continuity (infinite resistance / OL on the meter) when the relay is not energized.
    • Apply 12 volts from a small battery or power source (like a 9V battery might work, but a 12V source is better) to Terminals 85 and 86. You should hear a click.
    • Immediately check continuity between Terminals 30 and 87 again. Now there should be continuity (low resistance, near 0 Ohms). If continuity does not appear when power is applied to 85/86, the relay's internal switch is faulty. If there's continuity without power applied, the contacts are welded shut.

Replacing the 1991 Corvette Fuel Pump Relay

If testing confirms the relay is faulty, replacement is simple:

  1. Disconnect Battery: Always essential.
  2. Purchase Correct Replacement: Obtain a new relay. An exact OEM replacement (ACDelco Part# often D1745A or similar suffix letters may vary) is ideal. A high-quality aftermarket relay matching the original's specifications and terminal layout will also work. Bring the old relay to the parts store to match shape and terminal numbers/pattern. Ensure it's a 4 or 5-pin relay (SPST or SPDT) as applicable. Standard automotive relay part numbers like the Bosch 0 332 019 150 are often compatible, but verify specs.
  3. Insert New Relay: Align the pins on the new relay exactly with the holes in the socket. Press it firmly and evenly straight down until it seats completely. You should hear a distinct "click" when it snaps home.
  4. Reconnect Battery: Reconnect the negative battery cable.
  5. Test: Turn the ignition key to "Run" and listen for the fuel pump prime sound. Then attempt to start the engine. If the relay was the issue, the engine should start.

Crucial Considerations & Troubleshooting if the Relay Isn't the Problem

What if replacing the relay doesn't fix your no-start issue? The fuel pump circuit involves several other components:

  1. Fuel Pump Fuse: While the primary power to the fuel pump runs through the relay, there will be a fuse protecting that main circuit. In the 1991 Corvette, this critical fuse is the Fuel Pump Fuse (ENG/INJ fuse). Location: Inside the primary underhood electrical center (the large box next to the auxiliary relay block).
    • Carefully open the cover of the large electrical center. Locate the fuse panel diagram molded into the cover. Find the fuse labeled "ENGINE" or "INJ" or "FUEL PUMP." On the 1991, it's usually a 20-amp or 25-amp fuse located among the other engine control fuses.
    • Check it! Remove the fuse and visually inspect the tiny wire inside. If it's broken or the metal ends show signs of melting/burning, replace it with a fuse of the exact same amperage rating.
  2. Oil Pressure Sender/Switch Bypass: Corvettes (and many GM vehicles) incorporate a safety feature. If the oil pressure drops dangerously low (indicating potential engine damage), the circuit cuts power to the fuel pump to kill the engine. A secondary path for powering the fuel pump runs through the oil pressure sender (actually a switch on this circuit). How it affects diagnosis:
    • The PCM powers the pump via the relay during cranking and while running if the engine speed signal indicates it's running. However, once oil pressure builds above a certain threshold (around 4-6 psi), the oil pressure switch closes.
    • This closed switch provides an alternative power path directly from battery power (via a fuse) to the fuel pump, bypassing the fuel pump relay. This serves as a backup: if the relay fails while the engine is already running, the oil pressure switch takes over to keep the pump running using this alternative circuit.
    • During Start-up: If the fuel pump relay is bad, the car should crank but not start initially. However, if the engine does crank long enough to generate oil pressure (even briefly), and the oil pressure switch is working, then the fuel pump might suddenly get power via the backup circuit and the engine could start unexpectedly after prolonged cranking. This can mask a faulty fuel pump relay. If the engine starts only after cranking for an unusually long time (allowing oil pressure to build), suspect the primary circuit (likely the fuel pump relay). A completely failed relay might still prevent start-up, as the backup oil pressure circuit only activates once pressure exists.
  3. Faulty Fuel Pump: Of course, the electric fuel pump inside the fuel tank can fail. Common signs include a loud whining/groaning noise before failure, or simply no noise at all during prime. Testing pump voltage and ground at the tank access point is necessary to confirm a dead pump.
  4. Bad Fuel Pump Ground: The fuel pump requires a clean, solid ground connection to complete its circuit. Check the ground strap/wires, especially the main chassis ground behind the driver's seat (near the battery in the rear compartment) and the specific fuel pump ground connection location (refer to a service manual).
  5. Wiring Issues: Damage, corrosion, breaks, or shorts in the wiring harness between the relay, fuse, PCM, oil pressure switch, inertia switch, and the fuel pump itself can cause problems. Look for obvious damage, rodent damage near harnesses, or signs of corrosion in connectors (including the relay socket).
  6. Faulty PCM: While less common than other issues, a problem within the Powertrain Control Module (PCM) itself, such as failed drivers or internal corrosion, could prevent it from sending the signal to activate the fuel pump relay.
  7. Inertia Safety Switch (Fuel Cut-off Switch): Designed to cut fuel pump power in the event of a collision, a tripped or faulty inertia switch can also cause a no-fuel condition. Location: Typically mounted in the passenger footwell area (side kick panel) or rear compartment on C4 Corvettes. Consult a manual for the exact '91 location. The switch usually has a reset button that can be pressed if it was tripped by a significant impact or sometimes even just a bump.

(Recommended Image: Simplified Wiring Diagram specific to the 1991 Corvette fuel pump circuit. Clearly show Battery -> Main Fuse (ENG/INJ) -> Fuel Pump Relay contacts -> Oil Pressure Switch path -> Fuel Pump itself. Highlight the relay's control coil connection to the PCM and ignition power. Arrows indicating direction of current flow would be very helpful.)

Essential Safety Tips for Working on Fuel System Electrics

  • No Sparks! Always disconnect the battery negative terminal before working on fuel pumps, relays, or wiring. Fuel vapors are highly flammable.
  • Reliable Work Area: Work in a well-ventilated area.
  • Eye Protection: Wear safety glasses, especially when checking fuses or probing connections.
  • Correct Tools: Use a digital multimeter for accurate voltage, continuity, and resistance measurements. Ensure test leads are in good condition. Have a fuse puller tool handy.
  • Quality Parts: Use high-quality replacement relays and fuses. Cheap components can fail prematurely.
  • Know Your Limits: If diagnosing electrical issues is beyond your comfort level, consult a qualified Corvette technician. Diagnosing wiring faults can sometimes be complex.

1991 Specificity is Key

It's crucial to note that relay locations can vary slightly between model years, even within the C4 generation (1984-1996). While the auxiliary relay block location on the passenger front engine bay is consistent for many C4 years, the exact position within that block can differ. The information provided here specifically targets the 1991 Chevrolet Corvette with the 350 cu.in (5.7L) L98 engine. Ensuring you're looking at the front right corner of the auxiliary relay block near the passenger headlight is critical for this year.

Conclusion: Solving the "No Fuel" Puzzle Starts Here

Locating and understanding the 1991 Corvette fuel pump relay in the passenger-side auxiliary relay block (front right position) is fundamental diagnostic knowledge for any C4 owner. When your '91 won't start but cranks, this relay is a prime suspect. By following the precise location steps, safely removing and testing the relay, and knowing the simple swap method, you can quickly determine if this inexpensive component is the culprit. Remember that a bad relay can sometimes be masked by the oil pressure backup circuit causing the engine to start after prolonged cranking. If replacing the relay doesn't solve the problem, systematically check the associated fuse, listen for the pump, consider the oil pressure switch's role, and be prepared to explore the fuel pump itself or potential wiring issues. Keeping these electrical contacts clean and using quality components ensures reliable fuel pump operation, getting your 1991 Corvette back on the road where it belongs.

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